Black men with prostate cancer who are treated with chemotherapy live at least as long as white men and may respond better to treatment with Zytiga (abiraterone), according to a pair of studies presented this week at the American Society of Clinical Oncology (ASCO) annual meeting in Chicago.
“This study adds to the growing body of evidence showing that Black men with advanced prostate cancer who participate in clinical trials have the same, if not better, chance of survival as white men,” Robert Dreicer, MD, of the University of Virginia Cancer Center said in an ASCO press release. “This research shows that by providing equal access to treatment, we can reduce racial disparities in outcomes for men with advanced prostate cancer.”
Prostate cancer is the most common cancer (after noninvasive skin cancer) and the second leading cause of cancer death among men in the United States. Nearly 164,700 men will be diagnosed with prostate cancer and around 29,500 will die from it this year, according to the American Cancer Society.
Prostate cancer typically grows slowly and only a small proportion of men will die from it. But studies have shown that Black men are not only more likely than white men to develop prostate cancer but also are diagnosed at a younger age on average, tend to have more aggressive disease and are twice as likely to die from it. It is not yet clear whether these differences are attributable to genetic factors, disparities in access to care or some combination of these.
Susan Halabi, PhD, of Duke University in Durham, North Carolina, presented findings from a pooled analysis of data from nine Phase III clinical trials comparing overall survival among African-American and white men with advanced prostate cancer treated with chemotherapy. Each of the studies included too few Black men to conduct a racial comparison that would produce statistically significant results, meaning they probably are not attributable to chance alone.
The study population included 8,820 men with metastatic (spread beyond the prostate) cancer that had progressed despite the use of hormone therapy to lower testosterone levels, known as being castration-resistant. The median age was 69. Six percent identified as African American, 5 percent were Asian and 85 percent were white. Trials sponsored by the National Cancer Institute’s National Clinical Trials Network included a higher proportion of Black participants than those sponsored by pharmaceutical companies (12 percent versus 4 percent). Only the Black and white men were included in this analysis. They received chemotherapy regimens containing Taxotere (docetaxel) and prednisone, alone or in combination with other drugs.
The median overall survival was about 21 months for both Black and white men. But in a multivariate analysis that adjusted for established risk factors, including higher prostate-specific antigen (PSA) levels and worse overall health, African-American men had a 19 percent lower risk of death from all causes.
Halabi noted that this study looked at men participating in clinical trials, which may not reflect the population of men with prostate cancer as a whole. She said the researchers are planning to do genomic analysis to see whether genetic variations might help explain differences in outcomes by race.
Response to Zytiga
In the second study, Daniel George, MD, also from Duke, and colleagues looked at the response to Zytiga and prednisone in Black versus white men. Pivotal trials of Zytiga suggested that Black men might have higher response rates, but again these studies enrolled too few Black men to conduct definitive comparisons.
The Abi Race study included 100 men with metastatic castration-resistant prostate cancer, half of whom self-identified as Black and half as white. Again, the median age was about 69. The Black men were more than twice as likely to have high blood pressure. All were treated with Zytiga plus prednisone until they experienced disease progression or unacceptable side effects.
The median radiographic progression-free survival, meaning patients were still alive without disease progression as shown on imaging scans, was about the same for both Black and white men (16.7 and 16.5 months, respectively). But Black men went longer without rising PSA levels: 16.6 versus 11.5 months, respectively. The Black patients were also more likely to see their PSA levels decline by at least 30 percent, 50 percent or 90 percent, and they were less likely to experience no PSA decrease.
Side effects differed somewhat between the two groups. Black men were more likely to experience constipation and hot flashes and to develop high blood glucose and low potassium levels. White men reported more fatigue, vomiting and headaches.
Genomic sequencing revealed some key variations between the two groups in genes involved in androgen (male hormone) metabolism, which might help explain differences in response. The researchers are evaluating whether these variations might be used to predict response.
“Black men are more than twice as likely to die of prostate cancer than white men and are generally thought to have worse prostate cancer outcomes. Our study suggests that when Black men and white men with advanced prostate cancer are given the same hormone treatment, this is not the case. Our research underscores the importance of specifically studying genetically diverse populations and raising awareness of these results, so that everyone who can benefit from abiraterone is offered this treatment,” George said in another ASCO press release.
“Racial and ethnic minorities continue to be underrepresented in clinical trials,” Dreicer added. “This study should serve as a call for the entire cancer research community to make trials much more inclusive. When it comes to cancer treatments, people are not all alike, and it’s important to understand how different groups respond to different therapies.”
Click here to read the survival abstract.
Click here to read the Zytiga abstract.