A real-world study presented at the virtual 2021 ASCO Annual Meeting evaluated prostate-specific antigen pattern progression and its association with overall survival (OS) among patients with metastatic castration-resistant prostate cancer (CRPC) who were treated with enzalutamide or abiraterone.

In a real-world setting, prostate-specific antigen value is used among practitioners to monitor treatment outcomes in patients with metastatic CRPC, however, due to possible spurious “flare” reactions, early prostate-specific antigen changes are not accounted for in the definition of prostate-specific antigen progression.

Aiming to identify the significance of an early prostate-specific antigen increase in patients with metastatic CRPC treated with enzalutamide or abiraterone, Fernando López-Campos, MD, Radiation Oncology Department, Hospital Universitario Ramón y Cajal, Madrid, Spain, and colleagues conducted a retrospective evaluation.

Dr López-Campos and colleagues evaluated patients with metastatic CRPC who were treated with enzalutamide or abiraterone between 2011 and 2020, defining prostate-specific antigen progression as a 25% increase from baseline at 4 or 8 weeks after treatment initiation.

The association of prostate-specific antigen progression and OS in chemotherapy-naïve patients treated with enzalutamide or abiraterone was investigated through univariable and multivariable Cox regression models. Differences in the impact of prostate-specific antigen progression on OS in participating patients were examined through interaction tests.

Of the 511 patients included in this study, 391 (76.5%) were treated with abiraterone, and 120 (23.5%) were treated with enzalutamide. The median follow-up period among all participants was 30.2 months. Patients treated with enzalutamide had longer OS than those treated with abiraterone (38.1 months vs 29 months).

In patients treated with abiraterone, 15.1% experienced progression after 4 weeks of initial treatment, 17.9% after 8 weeks, and 12.3% after 12 weeks. In patients treated with enzalutamide, 7.5% experienced progression after 4 weeks of initial treatment, 9.2% after 8 weeks, and 8.3% after 12 weeks. Differences were not statistically significant.

In patients treated with abiraterone, prostate-specific antigen progression was associated with worse overall survival, compared with enzalutamide. In patients treated with enzalutamide, prostate-specific antigen progression at 4 weeks had a large impact on overall survival, which was not observed at 8 weeks or 12 weeks.

There was no significant interaction between agent and prostate-specific antigen progression.

“Prostate-specific antigen progression at 4 weeks after enzalutamide or abiraterone is significantly associated with shorter OS and may help identify patients not benefitting from enzalutamide or abiraterone before clinical or radiographic progression” wrote Dr López-Campos, concluding, “Prostate-specific antigen pattern progression and its association with OS might differ depending on the drug used (enzalutamide or abiraterone).”—Marta Rybczynski