BERKELEY, CA (UroToday.com) - Time to prostate-specific antigen nadir (TTPN) has long been investigated as a good predictor of progression-free survival (PFS) and overall survival (OS) in prostate cancer patients. However, the associations between TTPN and both PFS and OS were subjected to immortal time bias. Taking a patient with TTPN of 12 months as an example, he must have survived at least 12 months before he can have such TTPN; this favors a directly proportionate relationship between TTPN and survival outcomes. In order to minimize this immortal time bias, new outcome measurements of PFS beyond TTPN and OS beyond TTPN were introduced.
We investigated the prognostic significance of TTPN and its relationship to PFS beyond TTPN and OS beyond TTPN in metastatic prostate cancer patients after primary androgen deprivation therapy (ADT). Our study was divided into two parts. In the first part of our study, we demonstrated that TTPN was a significant prognostic indicator for both PFS beyond TTPN (HR 0.72, 95% CI 0.52-0.99, P=0.040) and OS beyond TTPN (HR 0.65, 95% CI 0.47-0.90, P=0.010). In the second part of our study, the median PFS and OS were plotted against TTPN on a monthly interval. Using the Spline method, the best-fitted model was identified. Interestingly, the relationship between TTPN and survival beyond TTPN appeared to consist of three phases. In the first phase, the survival beyond TTPN increased with TTPN. In the second phase, the survival beyond TTPN remained relatively static. In the third phase, the survival beyond TTPN increased exponentially with TTPN. Different TTPNs had different implications in predicting survival beyond TTPN. With excellent correlations between TTPN and survival beyond TTPN, we believe TTPN may serve as a good reference for deciding the best treatment strategy in metastatic prostate cancer patients who develop disease progression after primary ADT.
Written by:
Jeremy Y.C. Teoh, MBBS, MRCSEda and Ming-Kwong Yiu, FRCSEd (Urol), FHKAM (Surgery)b as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
aDivision of Urology, Department of Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong.
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bDivision of Urology, Department of Surgery, Queen Mary Hospital, The University of Hong Kong.
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