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