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Advanced Prostate Cancer

The Current Status of Immunotherapy for Prostate Cancer

The Prostate Cancer Immune Microenvironment

The microenvironment associated with prostate cancer includes low cytolytic activity of natural killer (NK) cells,5 high secretion of TGF-beta by prostate tissue (which inhibits NK and lymphocyte function),6 and recruitment of T regulatory cells that down-regulate antitumor immunity.7 As such, the prostate cancer microenvironment has been described as an immunosuppressive state. Furthermore, based on the chronicity of the prostate cancer disease spectrum, the immune microenvironment is likely dynamic, with changes over time/clinical states and with treatment exposure.8 For example, there are increased tumor-infiltrating lymphocytes in the prostate bed following androgen deprivation therapy,9 and higher levels of PD-1 ligand and PD-L2 expression on the surface of enzalutamide-treated prostate cancer cells.10 Several aspects make prostate cancer attractive for immunotherapy-based treatment options, including a high-level of tumor-associated antigens such as prostate-specific antigen (PSA), prostate acid phosphatase (PAP), and prostate-specific membrane antigen (PSMA).

Cell-based vaccines

Cell-based vaccines consist of whole cells that are modified in order to induce anti-tumor immune responses. Sipuleucel-T is an autologous vaccine processed following peripheral dendritic cell collection via leukapheresis. This is then incubated with GCS-F and PAP protein, followed by reinfusion into the patient (after a 36-44 hour period) in order to generate a PAP-specific CD4+ and CD8+ T cell response.11,12

Sipuleucel-T was FDA approved based on results of the Phase III IMPACT clinical trial.1 This trial enrolled 512 patients with mCRPC who had asymptomatic disease/minimally symptomatic with no visceral metastases, randomizing men to three infusions of sipuleucel-T (n=341) or placebo (n=171). The IMPACT trial noted a 4.1-month improvement in overall survival (OS) for those taking sipuleucel-T compared to placebo and a 22% reduction in risk of death. There was no difference between the groups with regards to objective disease progression or PSA response (secondary endpoints). An assessment of safety profile for patients in this study found that the treatment was overall well tolerated with minimal concern for severe adverse events.13 Furthermore, immunologic assessment showed that patients with high antibody titers against PA2024 benefited the most from treatment, noting longer survival.1 Despite the results and safety profile of IMPACT, reported nearly a decade ago, the use of sipuleucel-T has not been widely adopted primarily due to the lack of cost-effectiveness and the infrastructure required to administer this treatment.

Vector-based vaccines

Vector-based vaccines consist of genetically engineered nucleic acids that encode specific tumor-associated antigens transmitted by vectors such as bacterial plasmids or viruses. DNA-based vaccines can be incorporated by host cells and generate an immune response to recruiting antigen-presenting cells. pTVG-HP is a DNA plasmid vector vaccine that encodes PAP protein. pTVG-HP has been tested in the non-metastatic CRPC setting, demonstrating increased PSA doubling time from 6.5 months to 9.3 months after one year of treatment.14

PROSTVAC is a PSA-target pox-virus-based vaccine. PROSTVAC was tested in a Phase II study of 125 patients with minimally symptomatic mCRPC who were randomized to receive the vaccine or placebo.15 Although the study was negative for its primary endpoint of progression-free survival (PFS), OS after 3 years of follow-up was significantly increased by 8.5 months (25.1 vs 16.6 months; HR 0.56; p=0.0061).

PROSTVAC was subsequently tested in a Phase III trial that reported results earlier this year.16 Patients were randomly assigned to PROSTVAC (n = 432), PROSTVAC plus granulocyte-macrophage colony-stimulating (GMCS) factor (n = 432), or placebo (n = 433), stratified by PSA (< 50 ng/mL vs. >= 50 ng/mL) and lactate dehydrogenase (< 200 vs >= 200 U/L). The primary endpoint for this trial was OS, and secondary endpoints were patients alive without events (AWE): radiographic progression, pain progression, chemotherapy initiation, or death at 6 months. Unfortunately, neither active treatment had an effect on median OS: (i) PROSTVAC: 34.4 months, hazard ratio (HR) 1.01, 95% confidence interval (CI) 0.84-1.20 (ii) PROSTVAC plus GMCS factor: 33.2 months, HR 1.02, 95% CI 0.86-1.22 (iii) placebo: 34.3 months. Furthermore, AWE at 6 months was similar between the arms. Based on these results, the authors noted that focus is currently ongoing for combination therapies.

DCVAC/PCa is an autologous dendritic cell vaccine derived from mononuclear cells that are pulsed with killed prostate cancer cells. In a Phase I/II trial, there were 25 men with mCRPC that received DCVAC/PCa plus docetaxel, demonstrating good tolerability and a median OS of 19 months.17 Currently, there is a Phase III (VIABLE) trial of DCVAC/PCa ongoing, which began accrual in 2014, with a target of 1,170 patients and planned completion date in 2020.

Immune Checkpoint inhibitors

Checkpoint inhibitors are antibodies that target molecules, such as cytotoxic T-lymphocyte protein 4 (CTLA-4) or PD-1 and its ligand PD-L1. Among men with mCRPC, ipilimumab was tested in the Phase III for those who had progressed on docetaxel chemotherapy, randomizing 799 patients to ipilimumab or placebo after bone-directed radiotherapy.18 The primary endpoint was OS, with no difference between the groups (ipilimumab 11.2 months vs placebo 10 months; HR 0.85, p=0.053); however, there was a small benefit in PFS favoring ipilimumab (4.0 vs 3.1 months; HR 0.70, p < 0.0001). More recently, Beer et al.19 reported findings of another Phase III trial randomizing 602 patients (2:1) with metastatic chemotherapy-naïve CRPC to ipilimumab vs placebo. Similar to the post-docetaxel patients, there was no difference in OS between the groups (HR 1.11, 95% CI 0.88-1.39), however men receiving ipilimumab had improved PFS (5.6 months vs 3.8; HR 0.67, 95% CI 0.55-0.81) compared to those receiving placebo.

Pembrolizumab has recently moved into the mCRPC arena, receiving FDA approval in a tumor agnostic indication for MSI-high (MSI-H) mutation CRPC patients in 2017. A study from the Memorial Sloan Kettering Cancer Center assessed the prevalence of MSI-H/dMMR prostate cancer among 1,033 patients treated at their institution,20 finding that 32 (3.1%) had MSI-H/dMMR disease. This included 23 patients (2.2%) that had tumors with high MSIsensor scores, and 7 of the 32 MSI-H/dMMR patients (21.9%) with pathogenic germline mutation in a Lynch syndrome-associated gene. Eleven patients with MSI-H/dMMR CRPC received anti-PD-1/PD-L1 therapy and six of these had a greater than 50% decline in PSA levels. Based on these data, experts in the field of advanced prostate cancer feel that every mCRPC patient should be tested for MSI-H status and potential pembrolizumab eligibility.

The KEYNOTE-028 study was a trial of pembrolizumab in advanced solid tumors among patients with PD-1 expression ≥1% of tumor or stromal cells. Among 245 men screened, there were 35 PD-1% (14.3%) and 23 patients who enrolled.21 There were four partial responses, for an objective response rate of 17.4% and 8 of 23 (34.8%) patients had stable disease. Median duration of response was 13.5  months, and median PFS and OS were 3.5 and 7.9 months, respectively. Furthermore, the 6-month PFS and OS rates were 34.8% and 73.4%, respectively. Recently, off-label use of pembrolizumab among a heavily pre-treated population of mCRPC patients has recently been reported. At the 2019 ASCO GU meeting, Tucker and colleagues presented data on 51 patients, 86% of which had received three or more prior lines of therapy. Most patients had previously received abiraterone (88%), docetaxel (86%), enzalutamide (80%), and sipuleucel-T (74%). Among these patients, 16% had a >50% confirmed PSA decline with pembrolizumab, with 8% having >90% PSA decline. Fifty-nine percent of men were treated with some form of concurrent therapy along with pembrolizumab, most commonly enzalutamide (47%).

At the 2019 ASCO GU meeting, results of the Phase II KEYNOTE-650 were also presented. This trial tested the combination of nivolumab plus ipilimumab for men with mCRPC. There were two cohorts for this study: cohort 1 – asymptomatic or minimally symptomatic, who had progressed after at least 1 second generation hormone therapy with no prior chemotherapy, and cohort 2 – progression after chemotherapy. Overall response rates were 26% in cohort 1 and 10% in cohort 2, including two patients in each cohort who had a complete response. Median time to response was approximately two months. PSA response rate was 18% in cohort 1 and 10% in cohort 2.

Future Directions

Unlike many other tumor sites, to date, there has not been robust data to demonstrate a large role for immunotherapy in patients with mCRPC. However, there are several potential ways to increase immunotherapy response with the goal of improving the outcomes of immunotherapy for prostate cancer: (i) combination therapy, (ii) immune modulation, (iii) biomarkers for improving patient selection.

Options for combination therapies:

1) Combination of immunotherapies: multiple vaccines, vaccine plus an immune checkpoint inhibitor, or an immunocytokine plus an immune checkpoint inhibitor. KEYNOTE-650 combining nivolumab plus ipilimumab is an example of improved efficacy among patients receiving combination therapy.

2) Combinations with therapies to capitalize on immunologic synergy: these studies assess the effect of the addition of other accepted treatments such enzalutamide, poly ADP ribose polymerase PARP inhibitors, radium-223, and docetaxel to immunotherapy regimens.

3) Given the changing microenvironment of prostate cancer across disease states, beginning combination immunotherapy earlier (castration-sensitive) may improve the immunotherapeutic benefit.

There are several options of immunomodulatory agents that target the tumor microenvironment to improve immunotherapy efficacy. Docetaxel has been proven to induce immunogenic modulations, such as increasing expression of ICAM-1, MUC-1, and MHC class 1 molecules.22 Additionally, tasquinimod is an immunomodulatory agent that blocks S100A9, a key regulatory molecule of myeloid cells. In a Phase II trial of 206 asymptomatic chemotherapy-naïve mCRPC patients randomized to tasquinimod vs placebo, men receiving tasquinimod had significantly improved disease progression (7.6 vs 3.3 months, p = 0.0042).23 Unfortunately, a Phase III trial assessing tasquinimod did not improve OS (21.3 for tasquinimod vs 24 months for placebo, HR 1.10, p=0.25), however, there was an improvement in radiographic PFS (7.0 months vs 4.4 months, HR 0.64, p = 0.001).24

Biomarkers continue to be an active area of research, not just for the selection of appropriate patients for immunotherapy, but also for other treatment regimens for advanced prostate cancer (ie. BRCA status for selecting patients for PARP inhibitors).

As follows is a summary of several of the current biomarkers as related to immunotherapy and prostate cancer (adapted from Maia and Hansen8):

current biomarkers as related to immunotherapy and prostate cancer

As follows is a summary of ongoing, recruiting phase III trial assessing immunotherapy in prostate cancer:

ongoing recruiting phase III trial assessing immunotherapy in prostate cancer

Conclusion 

To date, immunotherapy in prostate cancer has been less successful than other cancer types, with only Sipuleucel-T demonstrating an OS advantage of 4.1 months in a Phase III trial. Given the plethora of other treatment options, Sipuleucel-T is uncommonly used. However, with improved combination therapy, immunomodulation and biomarkers in addition to ongoing Phase III trials, there are additional assessments and results in upcoming that may improve the immunotherapy landscape and add to the armamentarium of treatment options for men with advanced prostate cancer.

Published Date: November 2019

Written by: Zachary Klaassen, MD, MSc
References: 1. Kantoff PW, Higano CS, Shore ND, et al. Sipuleucel-T immunotherapy for castration-resistant prostate cancer. N Engl J Med. 2010;363(5):411-422.
2. Ryan CJ, Smith MR, Fizazi K, et al. Abiraterone acetate plus prednisone versus placebo plus prednisone in chemotherapy-naive men with metastatic castration-resistant prostate cancer (COU-AA-302): final overall survival analysis of a randomised, double-blind, placebo-controlled phase 3 study. Lancet Oncol. 2015;16(2):152-160.
3. de Bono JS, Oudard S, Ozguroglu M, et al. Prednisone plus cabazitaxel or mitoxantrone for metastatic castration-resistant prostate cancer progressing after docetaxel treatment: a randomised open-label trial. Lancet. 2010;376(9747):1147-1154.
4. Parker C, Nilsson S, Heinrich D, et al. Alpha emitter radium-223 and survival in metastatic prostate cancer. N Engl J Med. 2013;369(3):213-223.
5. Pasero C, Gravis G, Guerin M, et al. Inherent and Tumor-Driven Immune Tolerance in the Prostate Microenvironment Impairs Natural Killer Cell Antitumor Activity. Cancer Res. 2016;76(8):2153-2165.
6. Flavell RA, Sanjabi S, Wrzesinski SH, Licona-Limon P. The polarization of immune cells in the tumour environment by TGFbeta. Nat Rev Immunol. 2010;10(8):554-567.
7. Sfanos KS, Bruno TC, Maris CH, et al. Phenotypic analysis of prostate-infiltrating lymphocytes reveals TH17 and Treg skewing. Clin Cancer Res. 2008;14(11):3254-3261.
8. Maia MC, Hansen AR. A comprehensive review of immunotherapies in prostate cancer. Crit Rev Oncol Hematol. 2017;113:292-303.
9. Thoma C. Prostate cancer: Towards effective combination of ADT and immunotherapy. Nat Rev Urol. 2016;13(6):300.
10. Bishop JL, Sio A, Angeles A, et al. PD-L1 is highly expressed in Enzalutamide resistant prostate cancer. Oncotarget. 2015;6(1):234-242.
11. Drake CG. Prostate cancer as a model for tumour immunotherapy. Nat Rev Immunol. 2010;10(8):580-593.
12. Ren R, Koti M, Hamilton T, et al. A primer on tumour immunology and prostate cancer immunotherapy. Can Urol Assoc J. 2016;10(1-2):60-65.
13. Hall SJ, Klotz L, Pantuck AJ, et al. Integrated safety data from 4 randomized, double-blind, controlled trials of autologous cellular immunotherapy with sipuleucel-T in patients with prostate cancer. J Urol. 2011;186(3):877-881.
14. McNeel DG, Dunphy EJ, Davies JG, et al. Safety and immunological efficacy of a DNA vaccine encoding prostatic acid phosphatase in patients with stage D0 prostate cancer. J Clin Oncol. 2009;27(25):4047-4054.
15. Kantoff PW, Schuetz TJ, Blumenstein BA, et al. Overall survival analysis of a phase II randomized controlled trial of a Poxviral-based PSA-targeted immunotherapy in metastatic castration-resistant prostate cancer. J Clin Oncol. 2010;28(7):1099-1105.
16. Gulley JL, Borre M, Vogelzang NJ, et al. Phase III Trial of PROSTVAC in Asymptomatic or Minimally Symptomatic Metastatic Castration-Resistant Prostate Cancer. J Clin Oncol. 2019;37(13):1051-1061.
17. Podrazil M, Horvath R, Becht E, et al. Phase I/II clinical trial of dendritic-cell based immunotherapy (DCVAC/PCa) combined with chemotherapy in patients with metastatic, castration-resistant prostate cancer. Oncotarget. 2015;6(20):18192-18205.
18. Kwon ED, Drake CG, Scher HI, et al. Ipilimumab versus placebo after radiotherapy in patients with metastatic castration-resistant prostate cancer that had progressed after docetaxel chemotherapy (CA184-043): a multicentre, randomised, double-blind, phase 3 trial. Lancet Oncol. 2014;15(7):700-712.
19. Beer TM, Kwon ED, Drake CG, et al. Randomized, Double-Blind, Phase III Trial of Ipilimumab Versus Placebo in Asymptomatic or Minimally Symptomatic Patients With Metastatic Chemotherapy-Naive Castration-Resistant Prostate Cancer. J Clin Oncol. 2017;35(1):40-47.
20. Abida W, Cheng ML, Armenia J, et al. Analysis of the Prevalence of Microsatellite Instability in Prostate Cancer and Response to Immune Checkpoint Blockade. JAMA Oncol. 2018.
21. Hansen AR, Massard C, Ott PA, et al. Pembrolizumab for advanced prostate adenocarcinoma: findings of the KEYNOTE-028 study. Ann Oncol. 2018;29(8):1807-1813.
22. Hodge JW, Garnett CT, Farsaci B, et al. Chemotherapy-induced immunogenic modulation of tumor cells enhances killing by cytotoxic T lymphocytes and is distinct from immunogenic cell death. Int J Cancer. 2013;133(3):624-636.
23. Pili R, Haggman M, Stadler WM, et al. Phase II randomized, double-blind, placebo-controlled study of tasquinimod in men with minimally symptomatic metastatic castrate-resistant prostate cancer. J Clin Oncol. 2011;29(30):4022-4028.
24. Sternberg C, Armstrong A, Pili R, et al. Randomized, Double-Blind, Placebo-Controlled Phase III Study of Tasquinimod in Men With Metastatic Castration-Resistant Prostate Cancer. J Clin Oncol. 2016;34(22):2636-2643.

Epidemiology and Etiology of Prostate Cancer

In 2018 in the United States, there will be an estimated 164,690 new cases of prostate cancer (19% of all male cancer incident cases, 1st) and an estimated 29,430 prostate cancer mortalities (9% of all male cancer deaths, 2nd only to lung/bronchus cancer).1 Over the last four decades, there was a spike in prostate cancer incidence in the late 1980’s/early 1990’s secondary to the widespread adoption of prostate-specific antigen (PSA) testing for the asymptomatic detection of prostate cancer.2 Since 1991, prostate cancer mortality has decreased by more than 40% due to a combination of increased PSA screening and improvement in treatment.3 This article will discuss the epidemiology of prostate cancer, as well as focus on several important etiologic risk factors associated with the disease.

Epidemiology

Incidence
For the last 30+ years, prostate cancer has been the most common noncutaneous malignancy among men in the United States, with 1 in 7 men being diagnosed with the disease.4 Similar to the United States, prostate cancer is the second most commonly diagnosed malignancy among men worldwide, with 1.1 million new cases diagnosed per year.5 In developed countries, the age-standardized rate (ASR) of prostate cancer incidence is 69.5 per 100,000 compared to 14.5 per 100,000 in developing countries.5 Crude differences in incidence between developed and developing countries are likely secondary to poor use of screening6 and lower life expectancies in developing countries.

Mortality
Among all men in the United States, 1 in 38 men will die from prostate cancer.4 Prostate cancer ranks as the leading cause of cancer death globally, with the highest mortality rates noted in the Caribbean and Southern/Middle Africa.5 Furthermore, the ASR for mortality in developed countries is 10.0 per 100,000 compared to 6.6 per 100,000 in developing countries.5 Many hypotheses have been considered as to the decline in mortality seen in the United States after 1991, with the most commonly accepted (in addition to utilization of screening) being an increase in aggressive curative treatment of prostate cancer diagnosed in the 1980s.7,8

A Global Perspective
The incidence and epidemiology from a global perspective is much different than what may typically be seen in the United States and Europe. For example, in India the incidence of prostate cancer is a fraction (1.7-5.3 per 100,000) of other first world countries (North America: 83.2-173.7 per 100,000),6 but secondary to the sheer size of the population (1.2 billion) the crude prevalence of prostate cancer is on par with countries such as the United States, UK, France, and Italy. Despite greater awareness of prostate cancer screening, data from India suggest that 4% of patients <50 years of age present with metastatic disease. Among worldwide prostate cancer incidence, 14% of cases are diagnosed within the Asia-Pacific region, with a wide variation of incidence rates across the Asian-Pacific countries. In Latin American countries, prostate cancer represents 28% of all incidence cancers (highest) and 13% of all cancer mortalities (second after lung cancer). Specifically, in Trinidad and Tobago, Guyana and Barbados, the incidence is 3-4x that of the United States. Particularly in Cuba, the mortality rates continue to increase, despite greater adoption of screening.  The incidence of prostate cancer in the Middle East is higher than the Asian countries, specifically in Lebanon (37.2 per 100,000), Jordan (15.3 per 100,000), and Palestine (15.2 per 100,000). A closer look at the demographics at presentation among Middle Eastern men shows that 25% present with metastatic disease, with rates as high as 58% among men from Iraq. There are several hypotheses for the shift in incidence and prevalence of prostate cancer among non-North America/European countries, including (1) an increased awareness of prostate cancer leading to greater utilization of PSA testing, and (2) adoption of a more “Western” diet/lifestyle and less the traditional Indian/Asian/Mediterranean diet, particularly in the urban centers.

Unfortunately, a greater burden of disease among non-North American/European regions has presented several problems:

  1. A wide variation in incidence/prevalence across countries in these regions, particularly in Asia-Pacific and Latin America
  2. Huge discrepancies in quality and access to care between the private and public sector
  3. Poor access to newer standards of care, leading to high rates of surgical castration and limited access to radiation therapy (ie. for treatment of bone metastases)
  4. Limited organized cancer registries, thus grossly underestimating the true incidence and prevalence of prostate cancer
Age and Family History
Age is an established risk factor for prostate cancer, as men <40 years of age are highly unlikely to be diagnosed with prostate cancer, whereas men >70 years of age have a 1 in 8 chance of prostate cancer diagnosis.1 In a population-based analysis of more than 200,000 patients, increasing age was associated with higher 15-year cancer-specific mortality (CSM) rates: 2.3% for men diagnosed ≤50 years of age, 3.4% for men 51-60 years of age, 4.6% for men 61-70 years of age, and 6.3% for men ≥71 years of age.9

A family history of prostate cancer is also strongly predictive of a prostate cancer diagnosis. To be considered hereditary prostate cancer, a family must have three affected generations, three first-degree relatives affected, or two relatives diagnosed prior to age 55.10 Men with one first-degree relative previously diagnosed with prostate cancer have a risk of a prostate cancer diagnosis that is 2-3x that of individuals with no family history.11 Data on 65,179 white men from the PLCO cancer screening trial showed that men with a family history of prostate cancer had a significantly higher incidence of prostate cancer (16.9% vs 10.8%, p<0.01) and higher cancer-specific mortality (0.56% vs 0.37%, p<0.01).12

Race
Both prostate cancer incidence and mortality have been shown to be significantly related to race. African-Americans and Jamaicans of African descent have the highest incidence of prostate cancer in the world.1 Despite decreases in mortality since the 1990s among all races, death rates of African Americans are still 2.4x higher than Caucasian patients.13 Several studies have assessed possible reasons for this discrepancy. In an ad hoc analysis of the REDUCE trial, African American men had greater non-compliance with study-mandated2 and 4-year prostate biopsies, despite having greater prostate cancer risk (at 2-year biopsy),14 suggesting that population-level estimates of the excess prostate cancer burden in African American men may underestimate the degree of prostate cancer disparity. Gene expression assessment of prostate cancer specimens has noted numerous differentially expressed genes between African American and white patients, suggesting that there may be racial differences in androgen biosynthesis and metabolism.15 However, studies in mCRPC patients assessing clinical response to the potent anti-androgen abiraterone have not demonstrated racial differences when prospectively evaluated.16

The incidence of prostate cancer among races other than African-American and Caucasians is lower, including men of Asian descent living in the United States, although their incidence of prostate cancer is higher than those living within continental Asia.17 Interestingly, men moving from developing countries to high prostate cancer incidence countries demonstrate a shift in prostate cancer risk similar to that of their new country of residence.18 Ultimately, the relative components of genetics, socioeconomic factors, cultural, and environmental factors associated with racial differences observed are poorly understood.   

Trends
There has been a significant drop in prostate cancer incidence in the last decade (~10% annually per year from 2010-2014), likely secondary to a decrease in PSA testing after the US Preventative Services Task Force (USPSTF) Grade D recommendation for screening of men older than 75 years of age (2008) and subsequently all men (2012) due to concern for overdiagnosis and overtreatment.13,19 Following the USPSTF recommendations, an analysis of the National Cancer Database suggested that in the month after the recommendation, incident prostate cancer diagnoses decreased by 1,363 cases, followed by a drop of 164 cases per month thereafter for the first year (28% decrease in incident cases).20 There has been considerable debate as to whether patients present with the more advanced disease since the USPSTF recommendations with no general consensus.21 Recently, the USPSTF changed their recommendation for PSA screening among men aged 55-69 years of age to a Grade C, suggesting that men in this age bracket should undergo periodic PSA-based screening for prostate cancer based on a decision after discussion regarding the potential benefits and harms of screening with their clinician.22

Etiology and Risk Factors

Diet and Obesity
Initial evidence that diet and lifestyle may have a role in prostate cancer epidemiological outcomes was provided by ecological studies which demonstrated that men in Western countries had higher rates of prostate cancer than developing/non-Western countries.6 To strengthen this possible association, subsequent studies demonstrated that men from non-Western countries migrating to Western countries adopted similar lifestyle and prostate cancer risk as those in Western countries.23 Nonetheless, several prospective studies since these ecologic descriptions assessing self-reported dietary patterns of healthy foods and the risk of prostate cancer have failed to show an association with diet and risk of prostate cancer.24,25 Epidemiological evidence suggesting that statins reduce the risk of advanced stage prostate cancer suggests a possible role of cholesterol and prostate cancer risk.26 Regardless, the complexity of the Western diet and the association/interaction with healthier lifestyles are limitations to understanding how diet influences prostate cancer risk.  

Obesity has become an epidemic in the United States, and observational studies have suggested a modest increase in the risk of prostate cancer among obese individuals.27,28 The pathophysiology between obesity and prostate cancer is likely secondary to higher levels of estradiol, insulin, and free IGF-1 levels, as well as lower free testosterone and adiponectin levels.29 However, a clear pathophysiological explanation between obesity and prostate cancer is still uncertain and may be associated with lower serum PSA and larger prostates leading to fewer prostate biopsies.30   

Inflammation
Chronic inflammation has been implicated in the development of several cancers and may also be associated with prostate cancer. Possible etiologic factors suggested include: infectious agents, dietary carcinogens, hormonal imbalances, as well as physical and chronic trauma.31 As a result, intra-prostatic inflammation may lead to DNA damage, epithelial proliferation, cellular turnover, and angiogenesis.31 In men part of the placebo arm of the Prostate Cancer Prevention Trial (PCPT), those with at least one biopsy core of inflammation had an odds ratio (OR) of 1.78 (95%CI 1.04-3.06) for prostate cancer compared to men with no cores of inflammation.32 Furthermore, this association was even higher when considering a high-grade prostate cancer diagnosis (OR 2.24, 95%CI 1.06-4.71).32

Medications
As mentioned, there has been emerging evidence that HMG-CoA reductase inhibitors (statins) may be associated with a lower risk of prostate cancer mortality following diagnosis.33 Although there have been disparate results for the beneficial nature of statins and prostate cancer, a recent meta-analysis from observational studies of nearly 1 million patients noted that both post- and pre-diagnosis use of statins are beneficial for both overall survival (HR 0.81, 95%CI 0.72-0.91) and cancer-specific survival (HR 0.77, 95%CI 0.66-0.85).34 Nonetheless, the exact role statins play in prostate carcinogenesis/protection is still widely debated.

Similar optimism with statins has been associated with metformin use and prostate cancer outcomes. Among patients with diabetes, metformin has been associated with a significant dose-dependent benefit for both prostate cancer-specific (HR 0.76, 95%CI 0.64-0.89 for each additional six months of metformin use) and all-cause mortality.35 In a systematic review and meta-analysis of observational studies assessing clinical outcomes of patients with prostate cancer and metformin, medication use was marginally associated with a reduction in risk of biochemical recurrence (HR 0.82, 95%CI 0.67-1.01), but not associated with metastasis, prostate-cancer mortality or all-cause mortality.36

Genetics
Prostate cancer is known to have an extraordinarily complex genetic makeup, including somatic copy number alterations, point mutations, structural rearrangements, and changes in chromosomal number.37 It is estimated that 5-10% of all prostate cancers may be caused by dominantly inherited genetic factors.11 These include, but are not limited to HPC1, HPC2, HPC20, HPCX, PCAP, and CAPB.38 More famously are the mutations associated with BRCA1 and BRCA2 and the associated increase in the risk of clinically significant prostate cancer, and prostate cancer-specific mortality among men with screen-detected prostate cancer.39-41 Recent research has evaluated epigenetic markers for prostate cancer such as miRNA. The first report of miRNA and prostate cancer was reported in 2007,42 and since then many reports have implicated over 30 unique miRNAs and prostate carcinogenesis.

Conclusions

The epidemiology and etiology of prostate cancer are complex and multi-factorial. Prostate cancer remains a malignancy spanning the spectrum of localized/indolent disease to de novo advanced disease that is ultimately fatal. Although there are accepted differences in race and geography, the ultimate interplay between sociodemographic factors, environmental/lifestyle factors, and genetic differences remains to be fully elucidated.

Published Date: April 16th, 2019
Written by: Zachary Klaassen, MD, MSc
References:
  1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2018. CA Cancer J Clin. 2018;68(1):7-30.
  2. Potosky AL, Miller BA, Albertsen PC, Kramer BS. The role of increasing detection in the rising incidence of prostate cancer. JAMA. 1995;273(7):548-552.
  3. Etzioni R, Gulati R, Tsodikov A, et al. The prostate cancer conundrum revisited: treatment changes and prostate cancer mortality declines. Cancer. 2012;118(23):5955-5963.
  4. Brawley OW. Trends in prostate cancer in the United States. J Natl Cancer Inst Monogr. 2012;2012(45):152-156.
  5. Torre LA, Bray F, Siegel RL, Ferlay J, Lortet-Tieulent J, Jemal A. Global cancer statistics, 2012. CA Cancer J Clin. 2015;65(2):87-108.
  6. Center MM, Jemal A, Lortet-Tieulent J, et al. International variation in prostate cancer incidence and mortality rates. Eur Urol. 2012;61(6):1079-1092.
  7. Walsh PC. Cancer surveillance series: interpreting trends in prostate cancer--part I: evidence of the effects of screening in recent prostate cancer incidence, mortality, and survival rates. J Urol. 2000;163(1):364-365.
  8. Etzioni R, Tsodikov A, Mariotto A, et al. Quantifying the role of PSA screening in the US prostate cancer mortality decline. Cancer Causes Control. 2008;19(2):175-181.
  9. Gandaglia G, Karakiewicz PI, Abdollah F, et al. The effect of age at diagnosis on prostate cancer mortality: a grade-for-grade and stage-for-stage analysis. Eur J Surg Oncol. 2014;40(12):1706-1715.
  10. Potter SR, Partin AW. Hereditary and familial prostate cancer: biologic aggressiveness and recurrence. Rev Urol. 2000;2(1):35-36.
  11. Bratt O. Hereditary prostate cancer: clinical aspects. J Urol. 2002;168(3):906-913.
  12. Liss MA, Chen H, Hemal S, et al. Impact of family history on prostate cancer mortality in white men undergoing prostate specific antigen based screening. J Urol. 2015;193(1):75-79.
  13. Jemal A, Fedewa SA, Ma J, et al. Prostate Cancer Incidence and PSA Testing Patterns in Relation to USPSTF Screening Recommendations. JAMA. 2015;314(19):2054-2061.
  14. Freedland A, Howard LE, Vidal A, et al. Black Race Predicts Poor Compliance but Higher Prostate Cancer Risk: Results from the REDUCE Trial. AUA 2018. 2018.
  15. Wang BD, Yang Q, Ceniccola K, et al. Androgen receptor-target genes in african american prostate cancer disparities. Prostate Cancer. 2013;2013:763569.
  16. George DJ, Heath EI, Sartor O, et al. Abi Race: A prospective, multicenter study of black (B) and white (W) patients (pts) with metastatic castrate resistant prostate cancer (mCRPC) treated with abiraterone acetate and prednisone (AAP). J Clin Oncol. 2018;36(Suppl; abstr LBA5009).
  17. Yu H, Harris RE, Gao YT, Gao R, Wynder EL. Comparative epidemiology of cancers of the colon, rectum, prostate and breast in Shanghai, China versus the United States. Int J Epidemiol. 1991;20(1):76-81.
  18. Gronberg H. Prostate cancer epidemiology. Lancet. 2003;361(9360):859-864.
  19. Moyer VA, Force USPST. Screening for prostate cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2012;157(2):120-134.
  20. Barocas DA, Mallin K, Graves AJ, et al. Effect of the USPSTF Grade D Recommendation against Screening for Prostate Cancer on Incident Prostate Cancer Diagnoses in the United States. J Urol. 2015;194(6):1587-1593.
  21. Barry MJ, Nelson JB. Patients Present with More Advanced Prostate Cancer since the USPSTF Screening Recommendations. J Urol. 2015;194(6):1534-1536.
  22. Force USPST, Grossman DC, Curry SJ, et al. Screening for Prostate Cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 2018;319(18):1901-1913.
  23. Yatani R, Shiraishi T, Nakakuki K, et al. Trends in frequency of latent prostate carcinoma in Japan from 1965-1979 to 1982-1986. J Natl Cancer Inst. 1988;80(9):683-687.
  24. Wu K, Hu FB, Willett WC, Giovannucci E. Dietary patterns and risk of prostate cancer in U.S. men. Cancer Epidemiol Biomarkers Prev. 2006;15(1):167-171.
  25. Key TJ, Allen N, Appleby P, et al. Fruits and vegetables and prostate cancer: no association among 1104 cases in a prospective study of 130544 men in the European Prospective Investigation into Cancer and Nutrition (EPIC). Int J Cancer. 2004;109(1):119-124.
  26. Jespersen CG, Norgaard M, Friis S, Skriver C, Borre M. Statin use and risk of prostate cancer: a Danish population-based case-control study, 1997-2010. Cancer Epidemiol. 2014;38(1):42-47.
  27. MacInnis RJ, English DR. Body size and composition and prostate cancer risk: systematic review and meta-regression analysis. Cancer Causes Control. 2006;17(8):989-1003.
  28. Renehan AG, Tyson M, Egger M, Heller RF, Zwahlen M. Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies. Lancet. 2008;371(9612):569-578.
  29. Buschemeyer WC, 3rd, Freedland SJ. Obesity and prostate cancer: epidemiology and clinical implications. Eur Urol. 2007;52(2):331-343.
  30. Freedland SJ, Platz EA, Presti JC, Jr., et al. Obesity, serum prostate specific antigen and prostate size: implications for prostate cancer detection. J Urol. 2006;175(2):500-504; discussion 504.
  31. De Marzo AM, Platz EA, Sutcliffe S, et al. Inflammation in prostate carcinogenesis. Nat Rev Cancer. 2007;7(4):256-269.
  32. Gurel B, Lucia MS, Thompson IM, Jr., et al. Chronic inflammation in benign prostate tissue is associated with high-grade prostate cancer in the placebo arm of the prostate cancer prevention trial. Cancer Epidemiol Biomarkers Prev. 2014;23(5):847-856.
  33. Stopsack KH, Greenberg AJ, Mucci LA. Common medications and prostate cancer mortality: a review. World J Urol. 2017;35(6):875-882.
  34. Zhong S, Zhang X, Chen L, Ma T, Tang J, Zhao J. Statin use and mortality in cancer patients: Systematic review and meta-analysis of observational studies. Cancer Treat Rev. 2015;41(6):554-567.
  35. Margel D, Urbach DR, Lipscombe LL, et al. Metformin use and all-cause and prostate cancer-specific mortality among men with diabetes. J Clin Oncol. 2013;31(25):3069-3075.
  36. Raval AD, Thakker D, Vyas A, Salkini M, Madhavan S, Sambamoorthi U. Impact of metformin on clinical outcomes among men with prostate cancer: a systematic review and meta-analysis. Prostate Cancer Prostatic Dis. 2015;18(2):110-121.
  37. Schoenborn JR, Nelson P, Fang M. Genomic profiling defines subtypes of prostate cancer with the potential for therapeutic stratification. Clin Cancer Res. 2013;19(15):4058-4066.
  38. Gronberg H, Isaacs SD, Smith JR, et al. Characteristics of prostate cancer in families potentially linked to the hereditary prostate cancer 1 (HPC1) locus. JAMA. 1997;278(15):1251-1255.
  39. Mitra AV, Bancroft EK, Barbachano Y, et al. Targeted prostate cancer screening in men with mutations in BRCA1 and BRCA2 detects aggressive prostate cancer: preliminary analysis of the results of the IMPACT study. BJU Int. 2011;107(1):28-39.
  40. Akbari MR, Wallis CJ, Toi A, et al. The impact of a BRCA2 mutation on mortality from screen-detected prostate cancer. Br J Cancer. 2014;111(6):1238-1240.
  41. Castro E, Goh C, Olmos D, et al. Germline BRCA mutations are associated with higher risk of nodal involvement, distant metastasis, and poor survival outcomes in prostate cancer. J Clin Oncol. 2013;31(14):1748-1757.
  42. Porkka KP, Pfeiffer MJ, Waltering KK, Vessella RL, Tammela TL, Visakorpi T. MicroRNA expression profiling in prostate cancer. Cancer Res. 2007;67(13):6130-6135.

Prostate Cancer and Tumor Markers

The discovery of prostate-specific antigen (PSA) in the late 1970s and its widespread application and adoption in the 1980s and 1990s ushered in the prostate cancer screening and disease monitoring era. As the first tumor marker for prostate cancer, it is organ specific but not cancer specific.1 thus providing the opportunity for further tumor marker investigation. A potential biomarker must go through a rigorous vetting process from discovery → differentiation of case from control → ability to detect preclinical disease (defining a positive test) → indications for application and validation → cancer control studies.2 Secondary to the cost and time involved, biomarkers are rarely tested in large randomized controlled trials (RCTs). However, the development of the Prospective Randomized Open, Blinded Endpoint (PROBE) initiative for biomarker studies was designed to overcome spectrum and ascertainment bias and give guidance for validation studies.3 Biomarkers are typically evaluated based on their positive predictive value (probability that a positive test indicates the presence of disease) and negative predictive value (probability that a negative test indicates the absence of disease), entities that rely on the test’s specificity, sensitivity, and prevalence of the disease. This article will focus on briefly reviewing the clinical utility of several commonly used tumor markers associated with prostate cancer detection.

Blood

PSA
PSA is part of the kallikrein gene family located on chromosome 19 and functions as a serine protease, predominantly produced by prostate luminal cells. PSA in the serum is typically bound to proteins (~80% of PSA; complexed) or unbound (free PSA). The production of PSA is androgen dependent4 and in the absence of cancer varies with age,5 race,6, 7 and prostate volume.8 African-American men without prostate cancer have a higher PSA level compared to similar Caucasian men when assessed on a volume-to-volume ratio.9 Additionally, many studies have suggested that PSA in men with higher body mass index (BMI) have lower PSAs, a concept referred to as “hemodilution”:10 a greater plasma volume leading to lower hematocrit and PSA. Recent studies have provided further support for the hemodilution theory, in that only a fraction of lower PSA values in obese men are attributed to testosterone and dihydrotestosterone levels, with the remaining lower PSA explained presumably by hemodilution.11 The greatest contributor to elevated PSA is prostatic diseases, namely prostatitis, BPH and prostate cancer. Without question, the decrease in specificity associated with PSA and prostate cancer is an elevated PSA in men with prostatitis and/or BPH.

Free PSA (fPSA)
fPSA is PSA that is enzymatically inactive and non-complexed, making up 4-45% of total PSA;12 men with PSA from prostate cancer cells have a lower percentage of total PSA that is free, compared to those without prostate cancer.13 fPSA has FDA approval for men with a negative digital rectal examination (DRE) and total PSA level of 4-10 ng/mL, largely on the basis of a prospective study of men demonstrating a %fPSA (fPSA/total PSA) cutoff of 25% detecting 95% of prostate cancers, while avoiding 20% of biopsies.14 A generally acceptable cut-point ranges from 15-25%. Twenty years later, %fPSA is still used for clinically appropriate men, most commonly used in those with an elevated PSA and a negative prostate biopsy. In these men, studies have reported a 5% cancer under-detection rate and 21% cutoff for repeating prostate biopsy.15

Kallikreins
PSA, also known as human kallikrein 3 (hK3), is the most famous of the kallikreins, however, there are other kallikreins that have recently been explored as prostate cancer tumor markers. hK2 shares 80% amino acid homology with PSA, however, is weakly expressed in benign tissue and intensely expressed in prostate cancer tissue.16 Low-grade disease generally has low expression of hK2, whereas aggressive disease has high levels of expression.16 Recently, the hK2 kallikrein has been incorporated into a panel of kallikrein markers (total PSA, free PSA, intact PSA, and hK2, along with clinical information), commercially available as the 4KScore Test, used for calculating a patient’s percent risk for aggressive prostate cancer. First described in 2008, Vickers et al.17 tested the utility of the kallikrein panel in 740 men in the Swedish arm of the ERSPC screening trial. They found that adding free and intact PSA with hK2 to total PSA improved the clinical area under the curve (AUC) from 0.72 to 0.84. When the authors applied a 20% risk of prostate cancer as the threshold for biopsy, 424 (57%) of biopsies would have been avoided, missing 31 of 152 low-grade and 3 of 40 high-grade cancers.17 Since this study a decade ago, many studies have validated these findings, including among 6,129 men participating in the ProtecT study:18 the AUC for the four kallikreins was 0.719 (95%CI 0.704-0.734) vs 0.634 (95%CI 0.617-0.651, p<0.001) for PSA and age alone for any-grade cancer, and 0.820 (95%CI 0.802-0.838) vs 0.738 (95%CI 0.716-0.761) for high-grade prostate cancer. 

Prostate Health Index (phi)
The phi test combines total, free and [-2]proPSA into a single score for improving the accuracy of prostate cancer detection. In the seminal study leading to FDA approval, Catalona et al.19 assessed phi scores among 892 patients without prostate cancer and a PSA between 2-10 ng/mL. They found that an increasing phi score was associated with a 4.7-fold increased risk of prostate cancer and a 1.6-fold increased risk of Gleason score ≥ 4+3 disease at prostate biopsy. Furthermore, the phi score AUC exceeded that of %fPSA (0.72 vs 0.67) to discriminate high vs low-grade disease or negative biopsy. In a subsequent study, Loeb et al.20 confirmed the phi score’s ability to outperform total, free and [-2]proPSA for identifying clinically significant prostate cancer.

Urine

Prostate Cancer Antigen 3 (PCA3)
PCA3 is a long noncoding RNA shed into the urine that is not expressed outside the prostate and is associated with much higher expression in malignant than benign prostate tissue.21 Prior to collecting urine for a PCA3 test, a “rigorous” DRE is performed in order to enhance the sensitivity of the test. The commercial PCA3 score is reported as a ratio of urine PCA3 mRNA to urine PSA mRNA x 1000. The optimal cutoff is still debated, however in a contemporary comparative effectiveness review, Bradley et al.22 showed that a PCA3 threshold of 25 resulted in a sensitivity of 74% and specificity of 57% for a positive biopsy. This threshold led to FDA approval of the PCA3 test in 2012 among men with a prior negative prostate biopsy.

Since then, several groups have reported results of PCA3 in biopsy naïve men. In a retrospective review of 3,073 men undergoing initial biopsy, Chevli et al.23 found that the mean PCA3 was 27.2 for those without, and 52.5 for patients with prostate cancer. Prostate cancer was identified in 1,341 (43.6%) men; on multivariable analysis, PCA3 was associated with any (OR 3.0, 95%CI 2.5-3.6) and high-grade (OR 2.4, 95%CI 1.9-3.1) prostate cancer after adjusting for clinicopathologic variables. Furthermore, PCA3 outperformed PSA in the prediction of prostate cancer (AUC 0.697 vs 0.599, p<0.01) but did not for high-grade disease (AUC 0.682 vs 0.679, p=0.702).23

microRNAs (miRNAs)
miRNAs are small, noncoding single-stranded RNAs involved in the regulation of mRNA. Due to their short sequence (typically 19-22 nucleotides), miRNAs are highly stable in most body fluids (including urine) as they are resistant to RNase degradation.24 Several miRNAs have been implicated as potential biomarkers in prostate cancer diagnosis and management, including miRNA-141, miRNA-375, miRNA-221, miRNA-21, miRNA-182 and miRNA-187.25, 26 miR-187 detected in urine has been suggested as a candidate for improving the predictive value for a positive biopsy; a prediction model including serum PSA, urine PCA3, and miR-187 provided 88.6% sensitivity and 50% specificity (AUC 0.711, p = 0.001) for a positive biopsy.26 Ultimately, these miRNAs need to be further validated in terms of their ability to regulate various pathways important for prostate cancer management and their potential role as tumor markers.

Combining Tumor Markers

In an effort to improve the predictive accuracy of a positive biopsy, the last several years have seen a plethora of studies combining biomarkers to not only improve predictive accuracy above that offered by PSA, but also individual, newer biomarkers. As previously mentioned, the decrease in specificity associated with PSA and prostate cancer is secondary to an elevated PSA in men with prostatitis and/or BPH. The “perfect” biomarker (or combination) would delineate prostate cancer (and ultimately high-grade prostate cancer) from other benign entities.

Vedder et al.27 assessed the added value of %fPSA, PCA3, and 4KScore Test to the ERSPC prediction models among men in the Dutch arm of the ERSPC screening trial. Prostate cancer was detected in 119 of 708 men – adding %fPSA did not improve the predictive value of the risk calculators, however, the 4KScore discriminated better than PCA3 in univariate models (AUC 0.78 vs. 0.62; p=0.01). In the overall population, there was no statistically significant difference between the multivariable model with PCA3 (AUC 0.73) versus the model with the 4KScore (AUC 0.71; p=0.18). Among 127 men with a previous negative biopsy, Auprich et al.28 compared the performance of total PSA, %fPSA, PSA velocity (PSAV), and PCA3 at first, second and ≥ third repeat biopsy. At first repeat biopsy, PCA3 predicted prostate cancer best (AUC 0.80) compared with total PSA. A second repeat biopsy, %fPSA demonstrated the highest accuracy (AUC 0.82), and again at ≥ third repeat biopsy %fPSA demonstrated the highest accuracy (AUC 0.70).28 

This sampling of studies demonstrates that many combinations of biomarkers are being studied in an effort to improve detection of high-grade cancer and decrease the number of unnecessary biopsies. The next generation of biomarker combinations has and will continue to incorporate multi-parametric prostate MRI into predictive algorithms for clinically significant prostate cancer.29-31

Conclusions

For over four decades, research efforts have been directed towards improving the detection of prostate cancer and attempting to build on the predictive accuracy of the first prostate cancer tumor marker, PSA. With the United States Preventative Services Task Force’s 2012 recommendation for the urgent need to identify new screening efforts to better identify indolent versus aggressive disease, the last several years have seen a dramatic increase in prostate cancer biomarker options. As briefly highlighted, biomarker combinations studies have demonstrated improved predictive accuracy of positive biopsies; however, these combinations are far from perfect, are expensive and much work remains to be done. Furthermore, the specific indication (pre-biopsy, post-negative biopsy, active surveillance, etc) and a combination of tumor markers remain to be fully elucidated.

Published Date: April 16th, 2019
Written by: Zachary Klaassen, MD, MSc
References: 1. Partin AW, Carter HB, Chan DW, Epstein JI, Oesterling JE, Rock RC, et al. Prostate specific antigen in the staging of localized prostate cancer: influence of tumor differentiation, tumor volume and benign hyperplasia. J Urol. 1990;143:747-52.
2. Srivastava S. The early detection research network: 10-year outlook. Clin Chem. 2013;59:60-7.
3. Pepe MS, Feng Z, Janes H, Bossuyt PM, Potter JD. Pivotal evaluation of the accuracy of a biomarker used for classification or prediction: standards for study design. J Natl Cancer Inst. 2008;100:1432-8.
4. Henttu P, Liao SS, Vihko P. Androgens up-regulate the human prostate-specific antigen messenger ribonucleic acid (mRNA), but down-regulate the prostatic acid phosphatase mRNA in the LNCaP cell line. Endocrinology. 1992;130:766-72.
5. Partin AW, Criley SR, Subong EN, Zincke H, Walsh PC, Oesterling JE. Standard versus age-specific prostate specific antigen reference ranges among men with clinically localized prostate cancer: A pathological analysis. J Urol. 1996;155:1336-9.
6. Smith DS, Carvalhal GF, Mager DE, Bullock AD, Catalona WJ. Use of lower prostate specific antigen cutoffs for prostate cancer screening in black and white men. J Urol. 1998;160:1734-8.
7. Espaldon R, Kirby KA, Fung KZ, Hoffman RM, Powell AA, Freedland SJ, et al. Probability of an abnormal screening prostate-specific antigen result based on age, race, and prostate-specific antigen threshold. Urology. 2014;83:599-605.
8. Naya Y, Stamey TA, Cheli CD, Partin AW, Sokoll LJ, Chan DW, et al. Can volume measurement of the prostate enhance the performance of complexed prostate-specific antigen? Urology. 2002;60:36-41.
9. Fowler JE, Jr., Bigler SA, Kilambi NK, Land SA. Relationships between prostate-specific antigen and prostate volume in black and white men with benign prostate biopsies. Urology. 1999;53:1175-8.
10. Ohwaki K, Endo F, Muraishi O, Hiramatsu S, Yano E. Relationship between prostate-specific antigen and hematocrit: does hemodilution lead to lower PSA concentrations in men with a higher body mass index? Urology. 2010;75:648-52.
11. Klaassen Z, Howard LE, Moreira DM, Andriole GL, Jr., Terris MK, Freedland SJ. Association of Obesity-Related Hemodilution of Prostate-Specific Antigen, Dihydrotestosterone, and Testosterone. Prostate. 2017;77:466-70.
12. McCormack RT, Rittenhouse HG, Finlay JA, Sokoloff RL, Wang TJ, Wolfert RL, et al. Molecular forms of prostate-specific antigen and the human kallikrein gene family: a new era. Urology. 1995;45:729-44.
13. Catalona WJ, Beiser JA, Smith DS. Serum free prostate specific antigen and prostate specific antigen density measurements for predicting cancer in men with prior negative prostatic biopsies. J Urol. 1997;158:2162-7.
14. Catalona WJ, Partin AW, Slawin KM, Brawer MK, Flanigan RC, Patel A, et al. Use of the percentage of free prostate-specific antigen to enhance differentiation of prostate cancer from benign prostatic disease: a prospective multicenter clinical trial. JAMA. 1998;279:1542-7.
15. Stephan C, Lein M, Jung K, Schnorr D, Loening SA. Re: Editorial: can prostate specific antigen derivatives reduce the frequency of unnecessary prostate biopsies? J Urol. 1997;157:1371.
16. Darson MF, Pacelli A, Roche P, Rittenhouse HG, Wolfert RL, Saeid MS, et al. Human glandular kallikrein 2 expression in prostate adenocarcinoma and lymph node metastases. Urology. 1999;53:939-44.
17. Vickers AJ, Cronin AM, Aus G, Pihl CG, Becker C, Pettersson K, et al. A panel of kallikrein markers can reduce unnecessary biopsy for prostate cancer: data from the European Randomized Study of Prostate Cancer Screening in Goteborg, Sweden. BMC Med. 2008;6:19.
18. Bryant RJ, Sjoberg DD, Vickers AJ, Robinson MC, Kumar R, Marsden L, et al. Predicting high-grade cancer at ten-core prostate biopsy using four kallikrein markers measured in blood in the ProtecT study. J Natl Cancer Inst. 2015;107.
19. Catalona WJ, Partin AW, Sanda MG, Wei JT, Klee GG, Bangma CH, et al. A multicenter study of [-2]pro-prostate specific antigen combined with prostate specific antigen and free prostate specific antigen for prostate cancer detection in the 2.0 to 10.0 ng/ml prostate specific antigen range. J Urol. 2011;185:1650-5.
20. Loeb S, Sanda MG, Broyles DL, Shin SS, Bangma CH, Wei JT, et al. The prostate health index selectively identifies clinically significant prostate cancer. J Urol. 2015;193:1163-9.
21. de Kok JB, Verhaegh GW, Roelofs RW, Hessels D, Kiemeney LA, Aalders TW, et al. DD3(PCA3), a very sensitive and specific marker to detect prostate tumors. Cancer Res. 2002;62:2695-8.
22. Bradley LA, Palomaki GE, Gutman S, Samson D, Aronson N. Comparative effectiveness review: prostate cancer antigen 3 testing for the diagnosis and management of prostate cancer. J Urol. 2013;190:389-98.
23. Chevli KK, Duff M, Walter P, Yu C, Capuder B, Elshafei A, et al. Urinary PCA3 as a predictor of prostate cancer in a cohort of 3,073 men undergoing initial prostate biopsy. J Urol. 2014;191:1743-8.
24. Schwarzenbach H, Nishida N, Calin GA, Pantel K. Clinical relevance of circulating cell-free microRNAs in cancer. Nat Rev Clin Oncol. 2014;11:145-56.
25. Sharma N, Baruah MM. The microRNA signatures: aberrantly expressed miRNAs in prostate cancer. Clin Transl Oncol. 2018.
26. Casanova-Salas I, Rubio-Briones J, Calatrava A, Mancarella C, Masia E, Casanova J, et al. Identification of miR-187 and miR-182 as biomarkers of early diagnosis and prognosis in patients with prostate cancer treated with radical prostatectomy. J Urol. 2014;192:252-9.
27. Vedder MM, de Bekker-Grob EW, Lilja HG, Vickers AJ, van Leenders GJ, Steyerberg EW, et al. The added value of percentage of free to total prostate-specific antigen, PCA3, and a kallikrein panel to the ERSPC risk calculator for prostate cancer in prescreened men. Eur Urol. 2014;66:1109-15.
28. Auprich M, Augustin H, Budaus L, Kluth L, Mannweiler S, Shariat SF, et al. A comparative performance analysis of total prostate-specific antigen, percentage free prostate-specific antigen, prostate-specific antigen velocity and urinary prostate cancer gene 3 in the first, second and third repeat prostate biopsy. BJU Int. 2012;109:1627-35.
29. Johnston E, Pye H, Bonet-Carne E, Panagiotaki E, Patel D, Galazi M, et al. INNOVATE: A prospective cohort study combining serum and urinary biomarkers with novel diffusion-weighted magnetic resonance imaging for the prediction and characterization of prostate cancer. BMC Cancer. 2016;16:816.
30. Sciarra A, Panebianco V, Cattarino S, Busetto GM, De Berardinis E, Ciccariello M, et al. Multiparametric magnetic resonance imaging of the prostate can improve the predictive value of the urinary prostate cancer antigen 3 test in patients with elevated prostate-specific antigen levels and a previous negative biopsy. BJU Int. 2012;110:1661-5.
31. Perlis N, Al-Kasab T, Ahmad A, Goldberg E, Fadak K, Sayid R, et al. Defining a Cohort that May Not Require Repeat Prostate Biopsy Based on PCA3 Score and Magnetic Resonance Imaging: The Dual Negative Effect. J Urol. 2018;199:1182-7.
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