Pooled analysis
In the United States, black men are more likely to be diagnosed with prostate cancer in their 40s and 50s than white men and are often diagnosed with advanced-stage and higher grade cancers. Black men also have double the rate of prostate cancer-specific deaths as white men.
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Dr. Richard Schilsky
Black men, however, are underrepresented in clinical trials, making it difficult to draw firm conclusions about racial differences due to small sample sizes.
To overcome this problem, Dr. Halabi and colleagues pooled data on 8,452 patients with mCRPC - including 7,528 white men and 500 African American men – from nine randomized phase 3 trials of docetaxel and prednisone or a regimen containing those agents.
Median overall survival, the primary endpoint, was 21.0 months for black men and 21.2 months for white men.
In multivariate analysis adjusted for age, PSA, performance status, alkaline phosphatase, hemoglobin, and metastatic sites, the pooled hazard ratio (HR) for black vs. white men was 0.81 (P = .001) for all patients in the study, and when the analysis was restricted to those patients who received only docetaxel and prednisone (4,172), the results were similar, Dr. Halabi said.
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Dr. Robert Dreicer
“I would argue that what this tells us is pretty striking: that African-American men have potentially better survival by getting conventional therapy,” commented ASCO expert Robert Dreicer, MD, MS, from the University of Virginia in Charlottesville.
“The nihilism associated with prostate cancer in African-American men is not supported by this really interesting work,” he continued. “What it says to us is when we treat those with bad prostate cancer, African Americans, they do well.”
Abiraterone Study
In the abiraterone study, 50 men who self-identified as white and 50 as black were enrolled and treated with abiraterone acetate and prednisone until disease progression or intolerable toxicity.
Radiographic progression-free survival, the primary endpoint, was 16.8 months in each group. As previously noted, however, median PFS was 16.6 months for black patients, vs. 11.5 months for white men. Black men also had a longer median PSA PFS, with 82% of black men having a 30% or greater PSA decline, compared with 78% of white patients. Respective proportions of men having higher declines were 74% vs. 66% experiencing a PSA decline of at least 50%, and 48% vs. 38% having a decline of at least 90%.
Rates of tumor flare, however, were higher among African Americans, at 16% vs. 4%.
Adverse event rates were generally similar between the study arms, although more white than black patients experienced fatigue, and more black than white patients had hypokalemia.
Single-nucletoide polymorphism (SNP) profiling showed differences between the two groups in key genes involved in androgen metabolism and transport, which may explain the improved responses to abiraterone among African Americans.
“We talk about access to care; we have now demonstrated that if you treat African Americans with standard-of-care drugs for advanced prostate cancer, there’s compelling evidence that they respond as well or maybe better than white men,” Dr. Dreicer commented.
“[We are] beginning to understand the differences that drive differential responses,” he continued. “When African-American men are under-represented in clinical trials, the trial outcomes might be different, frankly, because people respond differently to drugs. I think those are the take homes.”
SOURCE: Halabi et al, George et al. ASCO 2018 Abstracts LBA5005 and LBA5009