4CPS-169 Effect of abiraterone versus enzalutamide on prostate specific antigen levels in metastatic castration resistant prostate cancer

Background and importance Enzalutamide (ENZ) and abiraterone (AA) are two drugs that have been shown to improve survival in patients diagnosed with metastatic castration resistant prostate cancer (CRPCm). There are no direct comparison studies of these two drugs, so comparative analyses may help therapeutic positioning. Aim and objectives To evaluate the response of both drugs, measured as an early decrease in prostate specific antigen (PSA) levels, in CRPCm patients. Material and methods A prospective study was carried out in a third level hospital in which all patients diagnosed with CRPCm receiving treatment with AA and ENZ as firstline therapy were included. The characteristics of the patients and the necessary clinical data were obtained from the electronic medical records. To evaluate the progression of PSA levels, their absolute variation was determined at 3 (VPSA3) and 6 (VPSA6) months from the beginning of treatment. Differences between the baseline characteristics of both groups of patients were evaluated using a Student’s t test. The same type of statistical analysis was used to study significant differences between AA and ENZ with respect to VPSA3 and VPSA6. The study was authorised by the Committee on Ethics of Drug Research (CEIm) of the centre of reference (code GNC-ABI-2017-01). Results In this study, 42 patients were included (mean age 78.3 years (66–92)), all with a Gleason score ≥7: 40.5% (n=17) of patients were treated with AA and 59.5% (n=25) with ENZ. No differences were observed between the two groups in their baseline characteristics: mean age 76.2 versus 79.8 years (p=0.054); mean PSA levels before initiation of AA were 32.9 ng/mL versus 59.0 ng/mL with ENZ (p=0.51). VPSA3 was higher in the group of patients treated with ENZ (−45.3 ng/mL) than in the AA group (+25.9 ng/mL, p=0.04). No differences were observed between groups for VPSA6 (AA versus ENZ: +28.1 ng/mL vs −10 ng/mL; p=0.23). Conclusion and relevance As described in previous studies, an early decrease (3 months) in PSA levels was greater in ENZ treated CRPCm patients. However, these differences in biochemical response were equal after 6 months of treatment. Although these results, to date, have not been correlated with effects on progression free survival or overall survival of patients, this effect could position ENZ as the therapeutic alternative in situations that require a rapid response. References and/or acknowledgements No conflict of interest.