Effects of Concurrent Administration of Spironolactone in Veterans with Metastatic Prostate Cancer Receiving Abiraterone: A Real-World Retrospective Study.

Introduction: Prostate cancer is the most common cancer in men in the United States with low survival rates once metastasized. Abiraterone is approved for use in castrate-sensitive and castrate-resistant prostate cancer and is used extensively in the Veterans Affairs (VA) healthcare system. Spironolactone, a diuretic used to treat heart failure, edema, ascites, and hypertension, may increase androgen levels and reduce effectiveness of abiraterone when used concurrently to treat prostate cancer patients. While previous case studies support this, no large epidemiology studies have been conducted. The current study utilizes the large, VA prostate cancer data core and evaluates the effect of concomitant spironolactone on efficacy of abiraterone treatment in metastatic prostate cancer patients.

Patients and methods: The study selected 18,943 veterans with metastatic prostate cancer on abiraterone treatment. Of these, 581 patients (3.1%) were also on concomitant spironolactone. The concomitant treatment group, abiraterone + spironolactone, significantly differed from the abiraterone-only group in body mass index, prevalence rates of heart failure and liver disease, and being previously treated with docetaxel. A 1:1 propensity score matching method was used to balance sample sizes and baseline traits between the two treatment groups, abiraterone versus abiraterone + spironolactone. Kaplan-Meier curves and Cox proportional hazard model were used to compare 5-year overall survival and all-cause mortality outcomes, respectively, between the two groups.

Results: After propensity score matched, the abiraterone + spironolactone group was treated with abiraterone significantly longer than the abiraterone-only group (mean ± standard deviation days 549.0 ± 552.3 vs. 435.5 ± 474.1; p = 0.0002) and had a higher 5-year overall survival rate (44% vs. 37%; p = 0.0116). Veterans with metastatic prostate cancer treated with abiraterone + spironolactone also had a lower 5-year all-cause mortality compared to those only on abiraterone (hazard ratio 0.80, 95% confidence intervals 0.61-0.96; p = 0.012).

Conclusion: This large VA observational study suggests that concomitant use of spironolactone does not compromise cancer control or survival of metastatic prostate cancer patients treated with abiraterone.