Evaluating real-world outcomes of abiraterone and enzalutamide in metastatic castrate-resistant prostate cancer

This study compared the real-world outcomes of two widely used drugs, abiraterone (Zytiga) and enzalutamide (Xtandi) in patients diagnosed with metastatic castrate-resistant prostate cancer (mCRPC). The study showed that both drugs were effective in these patients in a real-world setting, with better results with enzalutamide. 

CRPC is an advanced form of prostate cancer that does not respond to hormonal treatments such as androgen deprivation therapy (ADT). ADT lowers androgen levels such as testosterone (male sex hormone that helps prostate cancer grow and spread). CRPC is difficult to treat, particularly when it has spread beyond the prostate gland (mCRPC). 

Abiraterone and enzalutamide are both anti-androgen medications that are standard care drugs for mCRPC. These drugs are given along with ADT in these patients. In separate studies, both drugs have been shown to improve the outcomes of these patients. However, in clinical trials, patients are selected to have few or no other medical conditions and be fit. There is no data that directly compares the effectiveness of abiraterone and enzalutamide in men with mCRPC in a real-world setting.

75 patients with mCRPC who were treated with either abiraterone (38 patients) or enzalutamide (37 patients) in the last 6 years were included in the study. Patients were followed up for an average of 37 months. The primary outcome measured during the study was prostate-specific antigen (PSA; a protein made by the prostate gland used as a marker for prostate cancer) response rates. PSA response was defined as a 50% or more reduction in the PSA level.

Overall, 54% of patients had a prostate-specific antigen (PSA) response (reduction). PSA is a protein produced by the prostate gland that increases in prostate cancer and decreases as a response to prostate cancer treatments. 70.3% of patients in the enzalutamide group had a PSA response compared to 39.5% in the abiraterone group.

The time until PSA increased again, as well as the time until tumors started growing again on imaging scans was 7 months in the enzalutamide group compared to 5 months in the abiraterone group. 

The overall survival was longer in the enzalutamide group (29-30 months) compared to the abiraterone group (7-15 months). This was true regardless of the chemotherapy regimens patients had received before.

More patients in the enzalutamide group needed dose reductions (35%) compared to those in the abiraterone group (13%).

 The study showed that both enzalutamide and abiraterone were effective for patients with mCRPC in a real-world setting. Outcomes tended to be in favor of enzalutamide. 

The study was done at only one site in Australia. Therefore, the results may not be applied to a bigger population. Also, patients had different severities of the disease. Therefore, the difference in response and survival may be caused by the differences in disease severity.