BACKGROUND

This study investigated the prognostic significance of time to the prostate-specific antigen nadir (TTPN) and its relationship to survival beyond TTPN in metastatic prostate cancer after primary androgen-deprivation therapy (ADT).

METHODS

All metastatic prostate cancer patients treated with primary ADT from 2000 to 2009 were reviewed. The prognostic significance of TTPN in predicting progression-free survival (PFS) beyond TTPN and overall survival (OS) beyond TTPN was analyzed using the Cox regression model. The median PFS and OS were plotted against TTPN on a monthly interval. The PFS beyond TTPN and the OS beyond TTPN with reference to TTPN were calculated and presented.

RESULTS

The study enrolled 419 patients with a median follow-up period of 38 months. The findings showed that TTPN was a significant prognostic indicator for both PFS beyond TTPN (hazard ratio [HR] 0.72, 95 % confidence interval [CI] 0.52-0.99, p = 0.04) and OS beyond TTPN (HR 0.65, 95 % CI 0.47-0.90, p = 0.01) according to Cox regression analyses. The relationship between TTPN and survival beyond TTPN consisted of three phases. In the first phase (<3 months for PFS and <6 months for OS), the survival beyond TTPN increased with TTPN. In the second phase (3-17 months for PFS and 6-20 months for OS), the survival beyond TTPN remained relatively static. In the third phase (>17 months for PFS and >20 months for OS), the survival beyond TTPN increased exponentially with TTPN.

CONCLUSIONS

In this study, TTPN was a good prognostic indicator for PFS beyond TTPN and OS beyond TTPN in metastatic prostate cancer cases after primary ADT. Different TTPNs had different implications for predicting survival beyond TTPN.