Tumors from African-American men also were more likely, however, to have indicators of increased sensitivity to radiation therapy: decreased expression of the double-strand DNA repair pathway (p<0.001), increased expression of immune pathways (p<0.001), and increased radiosensitivity as predicted by a 24-gene prostate cancer radiation sensitivity score developed by the research team. Increased radiotherapeutic sensitivity suggests that African-American patients have improved outcomes when treated with radiation.
“Differences in gene expression between African-American and Caucasian patients revealed that African-American patients had lower DNA repair and more immunogenic tumors, both of which have been shown to predict better responses to radiation therapy,” said Dr. Spratt.
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Next, researchers examined outcomes from 5,854 patients (19.3 percent African-American) in four large NRG Oncology/RTOG randomized prostate cancer trials (NRG-RTOG 9202, 9408, 9413 and 9910). This meta-analysis showed that African-American men treated with radiation therapy, compared to Caucasian men, were less likely to see their cancer return or spread.
Specifically, African-American patients in these trials had lower rates of biochemical cancer recurrence (hazard ratio (HR) 0.82, 95% CI 0.74, 0.92; p=0.0005) and distant metastasis (HR 0.70, 95%CI 0.57, 0.86; p=0.0008), even after controlling for age, performance status, PSA, Gleason grade, T-stage, N-stage and hormone therapy use.
Dr. Spratt, who also co-chairs the radiobiology and radiotherapy working group for the Prostate Cancer Foundation, said the team’s findings, coupled with other recent analyses, confirm that the seeming racial disparities for prostate cancer are rooted more in societal causes than biology.
“Our results directly question previously held beliefs from population-based registry data that African-American men independently have worse prostate cancer outcomes than Caucasian men,” he explained. “These findings strengthen the notion that most of the observed disparity found in population datasets regarding stage-for-stage outcomes between African-American and Caucasian men are reflective of social constructs and not rooted in biology.”
“Not only did both groups generally have similar prognoses, but African-American men treated with radiation therapy actually had higher rates of cure and excellent outcomes. Patients should be treated irrespective of race,” he added.
The abstract, “Androgen receptor activity and radiotherapeutic sensitivity in African-American men with prostate cancer: A large scale gene expression analysis and meta-analysis of RTOG trials,” will be presented in detail during a news briefing and the plenary session at ASTRO’s 60th Annual Meeting in San Antonio.
