(UroToday.com) The 2024 GU ASCO annual meeting featured a prostate cancer session and a presentation by Dr. Ridvan Demirci discussing the association between SPECT/CT total tumor volume and new lesions in early cycles of 177Lu-PSMA-617 and progression-free and overall survival in men with metastatic castration-resistant prostate cancer (mCRPC). LuPSMA is a newly established treatment in patients with mCRPC,1 but PSA and survival outcomes vary widely, and predictors of treatment responses are needed. LuPSMA delivers radiation to tumor tissues that can also be imaged with SPECT/CT which provides semi-quantitative estimates of total tumor volume and identification of new lesions. This study investigated the use of SPECT/CT in early cycles to predict LuPSMA outcomes.
Between June 2022 and December 2022, mCRPC patients who initiated the second cycle of LuPSMA with SPECT/CT 24 hours post-treatment were retrospectively reviewed. Dr. Demirci and colleagues evaluated associations between total tumor volume and the appearance of new lesions at the start of the second or third cycle with PFS and OS using Cox regression analysis. New lesions were classified as non-PSMA-avid with no or low uptake (< liver) with corresponding findings on CT and PSMA-avid (uptake > liver). Associations between total tumor volumes and new lesions at cycle 2 and 3 with subsequent endpoints were evaluated using Cox regression, and all analyses were adjusted for change in PSA relative to baseline.
There were 66 mCRPC patients (median age 73.5 years) that received a median of 4 (IQR: 3-5) cycles of LuPSMA:
The median follow-up starting at the second cycle and third cycle was 42 weeks (IQR: 33-48) and 36 weeks (IQR: 27-41), respectively, with 47/66 (71%) alive at the time of the analysis. A reduction of ≥50% in PSA (PSA50) was noted in 33/66 (50%) of patients. Changes in PSA and total tumor volume at second and third cycle were concordant in 50/66 (76%) and 42/51 (82%) of patients, and were significantly correlated (r= 0.55 and 0.56, both p<0.001). Patients with higher absolute total tumor volume adjusted for PSA change at second cycle had worse PFS and OS with consistent results at third cycle:
New lesions were detected in 13/66 (7/13 PSMA-avid, 6/13 non-PSMA-avid) and 7/51 patients (5/7 PSMA-avid, 2/7 non-PSMA-avid) at the second and third cycle, respectively:
Patients with new lesions at 2nd cycle had higher risks of progression and death (HR 5.15 and HR 6.76).
Dr. Demirci concluded his presentation by discussing the association between SPECT/CT total tumor volume and new lesions in early cycles of 177Lu-PSMA-617 and progression-free and overall survival in men with mCRPC with the following take-home points:
- Higher SPECT/CT total tumor volume at second and third cycle and detection of new lesions at second cycle were associated with higher risks of progression and death
- Although changes in PSA and total tumor volume were correlated, absolute SPECT/CT total tumor volume in early cycles provided a complementary ability to predict outcomes of LuPSMA
Presented by: Ridvan Arda Demirci, University of Washington, Seattle, WA
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Associate Professor of Urology, Georgia Cancer Center, Wellstar MCG Health, @zklaassen_md on Twitter during the 2024 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, San Francisco, CA, January 25th – January 27th, 2024
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