SAN FRANCISCO-African-American men with advanced prostate cancer live longer as compared with white men when treated with newer hormonal therapies.
A large, retrospective study analyzing 5 years of data from the Veterans Health Administration (VHA) provides the first evidence that African-American men who are chemotherapy-naive with metastatic castration-resistant prostate cancer may have better overall survival than white men when treated with the newer prostate cancer drugs abiraterone acetate or enzalutamide.
"We've historically seen that prostate cancer is more common, more aggressive, and more lethal in African-Americans compared with men of other racial groups," said lead author Megan McNamara, MD, Assistant Professor of Medicine at the Duke University School of Medicine in Durham, N.C. "Balancing against other health-related risks, we found that treatment with newer hormonal medicines led to a significantly greater survival for African-American men in this analysis, compared with white men."
McNamara presented the results of the study at a presscast before the 2019 Genitourinary Cancers Symposium (Abstract 212).
Evidence suggests that African-American men with metastatic castration-resistant prostate cancer may have better outcomes in response to several prostate cancer treatments as compared to whites. "An analysis of pooled data from men with metastatic castration-resistant prostate cancer treated with docetaxel or a docetaxel-containing regimen in nine different randomized, phase III trials showed better overall survival among African-Americans treated with docetaxel as compared to whites, after adjusting for established prognostic factors. Similarly, African-American patients had longer survival compared to white patients when treated with sipuleucel-T in an exploratory analysis of the phase III trials, which was confirmed in the PROCEED registry," said McNamara.
A third study suggested African-American metastatic castration-resistant prostate cancer patients may have better prostate-specific antigen (PSA) response to abiraterone as compared to white patients, although no differences in progression were found, she noted.
With a paucity of real-world studies evaluating survival in African-American and white chemotherapy-naive metastatic castration-resistant prostate cancer patients treated with new hormonal therapies, the researchers analyzed VHA data from April 2013 to March 2018, focusing on adult men with prostate cancer whose only prior treatment was surgical or medical castration. Among men with disease that had progressed, researchers included only those who had been treated with either abiraterone acetate or enzalutamide. These medications were approved in 2013 and 2014, respectively, for use in men with metastatic castration-resistant prostate cancer who had not received chemotherapy.
Investigators monitored patients' health outcomes until they disenrolled from the VHA or died. The analysis included data from 2,123 white men with a mean age of 74 years, and 787 African-American men who had a mean age of 71 years with metastatic castration-resistant prostate cancer. African-American men were more prone to have hypertension, type 2 diabetes, and liver damage or abnormality as compared with white men.
Overall survival was defined as the interval from the first prescription claim for abiraterone or enzalutamide following castration (index date) to the date of death.
Key Findings
After adjusting for demographic and clinical characteristics available in the VHA database, researchers found that African-American men treated with either hormone therapy lived for a median of 30 months as compared with 26 months for white men.
"In univariate Cox analysis, African-Americans treated with abiraterone acetate or enzalutamide had better overall survival than whites. This was confirmed in multivariate Cox analysis, which adjusted for age and comorbidities," noted McNamara.
"When controlling for access to care (through a single-payer system) in chemotherapy-naive metastatic castration-resistant prostate cancer patients, African-Americans may have better overall survival than whites treated with abiraterone acetate or enzalutamide. These retrospective data emphasize the need for prospective trials to validate these findings and investigate the mechanism underlying racial disparities in survival outcomes of metastatic castration-resistant prostate cancer patients treated with new hormonal therapies."
She added that the results reinforce the current standard of care treatments. "It's important that we have real-world studies," stated McNamara. "All African-Americans should have availability for these medicines."
Next Steps
Initial findings of an earlier prospective clinical trial demonstrated better PSA response among African-American men with metastatic castration-resistant prostate cancer treated with abiraterone acetate as compared with white men. Additional analyses of blood samples from that trial are ongoing to investigate whether variations in key genes involved in androgen metabolism and transport may help explain some of the biology behind racial differences in treatment response.
"An important goal of the study is to understand why some men respond better to certain treatments for prostate cancer than others so that we can tailor treatments more effectively," said McNamara. "Finding biomarkers that can guide development of targeted therapies is the ultimate goal."
ASCO Expert Robert Dreicer, MD, MS, Deputy Director of the UVA Cancer Center and moderator of the presscast, commented: "This provocative data adds to the way we think of racial differences in prostate cancer. When it comes to cancer treatments, it's important to understand how different groups respond to different therapies. Mining historic records in large databases can often help researchers home in on the patients who are more likely to benefit from certain medications.
"These findings provide important evidence that African-American men with metastatic prostate cancer, who have long had among the highest incidence and poorest outcomes of this disease, may now have better survival when treated with newer prostate cancer medications as compared with other men."
Mark L. Fuerst is a contributing writer.