Obesity associated with prostate cancer risk in African-American men

Obesity was associated with an increased risk for prostate cancer in African American men and that risk grew by nearly four times as body-mass index (BMI) increased, according to an article published online by JAMA Oncology.

African American men have the highest incidence of prostate cancer of any racial or ethnic group in the United States, as well as the highest rates of aggressive disease and prostate cancer death. These elevated risks likely arise from both social and biologic factors. The associations of obesity with prostate cancer risk are complex.

Wendy E. Barrington, Ph.D., of the University of Washington School of Nursing and the Fred Hutchinson Cancer Research Center, Seattle, and coauthors compared the associations of obesity with prostate cancer risk between African American and non-Hispanic white men. The authors used data from 3,398 African American and 22,673 non-Hispanic white men who had participated in the Selenium and Vitamin E Cancer Prevention (SELECT) Trial (2001-2011). Outcomes for the present analysis were total, low-grade (Gleason score less than 7) and high-grade (Gleason score greater than or equal to 7) prostate cancer incidence.

During a median follow-up of 5.6 years, 1,723 men developed prostate cancer (270 total cases among African American men and 1,453 total cases among non-Hispanic white men). Overall, the study found a 58 percent increased risk for prostate cancer among African American men compared with non-Hispanic white men.

Obesity was not associated with risk for prostate cancer overall among non-Hispanic white men but there was a significant association between obesity and the risk for total (both low and high grade) prostate cancer in African American men. For example, being African American increased the risk for prostate cancer across BMI categories, jumping from 28 percent among African American men with a BMI less than 25 to 103 percent among African American men with a BMI of at least 35, according to the results.

For low-grade cancer, obesity was inversely associated with prostate cancer risk among non-Hispanic white men; those with a BMI of at least 35 had a 20 percent reduced risk compared with those non-Hispanic white men with a BMI less than 25. However, obesity was positively associated with the risk of high-grade prostate cancer among non-Hispanic white men.

Among African American men, obesity was positively associated with risks for both low- and high-grade prostate cancer, according to the study results.

The authors note the reasons underlying their findings are unknown but they speculate that one explanation may be that the biological effects of obesity differ in African American and non-Hispanic white men.

"This study reinforces the importance of obesity prevention and treatment among African American men, for whom the health benefits may be comparatively large. Although obesity is linked to poor health outcomes in all populations, clinicians might consider the unique contribution of obesity prevention and treatment to the health of their AA [African American] patients. Such targeted efforts may contribute to reductions in prostate cancer disparities," the article concludes.

In a related editor's note, Charles R. Thomas Jr., M.D., a deputy editor of JAMA Oncology, writes: "There appears to be a four times greater risk of developing prostate cancer in African American men as the BMI increases (28 percent for BMI < 25 vs. 103 percent for BMI ? 35). Furthermore, the risk of developing high-grade disease (defined as a Gleason score ? 7) was associated with higher BMI in all patients, although the risk was higher in African American men compared with non-Hispanic white men (hazard ratio, 1.81 percent). Despite the limitations inherent in the methodology utilized for the analysis and the inability to define a clear mechanism behind the association between BMI and risk, the findings do provide a further rationale for weight reduction and a target BMI for clinicians to aim for in care of African American men."

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(JAMA Oncol. Published online April 16, 2015. doi:10.1001/jamaoncol.2015.0513. Available pre-embargo to the media at http://media.jamanetwork.com.)

Editor's Note: SELECT was funded in part by Public Health Service grants from the National Cancer Institute and the National Center for Complementary and Alternative Medicine of the National Institutes of Health. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

Media Advisory: To contact corresponding author Wendy E. Barrington, Ph.D., call Kristen Woodward at 206-667-5095 or email kwoodwar@fredhutch.org. To contact Editor's note author Charles R. Thomas, Jr., M.D., call 312-464-5262 or email mediarelations@jamanetwork.org.