Negative Delta-Prostate-Specific Antigen Time Ratio as Potential New Marker of Progression-Free Survival in Castration-Resistant Prostate Cancer Patients Treated With First-Line Enzalutamide or Docetaxel

Purpose: We propose a new potential marker of progression-free survival (PFS) called negative delta-prostate-specific antigen (PSA) time ratio (NDPSATR) and compare it with conventional PSA response, defined as PSA decline ≥50% at 12 weeks from pretreatment baseline (PSAR50) in metastatic castration-resistant prostate cancer (mCRPC) patients treated with first-line enzalutamide (ENZ) or docetaxel (DTX).Materials and Methods: All patients diagnosed as mCRPC at Ajou University Hospital from 2016 were included. Delta-PSA days is PSA change between 2 consecutive measurements during a regimen multiplied by interval days. A negative delta-PSA days value represents a positive PSA response. NDPSATR is calculated by dividing the sum of days on negative delta-PSA days by total days on the regimen. Student t-test was used to compare mean values and Kaplan-Meier survival curves for PFS were obtained.Results: Of 57 patients identified, 22 and 35 were treated with ENZ and DTX, respectively. Rates of PSAR50 for ENZ and DTX were 72.7% and 20.6%, respectively. Mean NDPSATR for ENZ and DTX were 0.40 and 0.46, respectively and the difference was not statistically significant. For ENZ, median PFS (mPFS) of PSAR50 and non-PSAR50 were 14.3 and 4.8 months, respectively and there was significant difference in PFS (p=0.002). For DTX, mPFS of PSAR50 and non-PSAR50 were 15.0 and 6.5 months, respectively but there was no significant difference in PFS (p=0.055). At cutoff value of 0.4, rate of NDPSATR ≥0.4 for ENZ and DTX were 36.4% and 62.9%, respectively. For ENZ, mPFS of NDPSATR ≥0.4 and NDPSATR <0.4 were not achieved and 14.1 months, respectively and there was no significant difference in PFS (p=0.895). For DTX, mPFS of NDPSATR ≥0.4 and NDPSATR <0.4 were 9.7 and 6.3 months, respectively and there was a significant difference in PFS (p=0.045).Conclusions: NDPSATR ≥0.4 may be a good marker of PFS in CRPC patients treated with DTX and may replace PSAR50.