Does Obesity Explain the High Risk for Prostate Cancer in Black Men?

Veronica Hackethal, MD

April 16, 2015

Black men who are obese are at higher risk for prostate cancer than non-Hispanic white men, according to a study published online April 16 in JAMA Oncology.

In fact, results suggest that, for black men, the risk for prostate cancer nearly quadruples as body mass index (BMI) increases.

The relation between obesity and prostate cancer risk is different in black men than in non-Hispanic white men, said Wendy Barrington, PhD, MPH, from the University of Washington School of Nursing and the Fred Hutchinson Cancer Research Center in Seattle.

In black men, "obesity substantially increases the risks of both low- and high-grade prostate cancer," she explained in an interview with Medscape Medical News. In contrast, in white men, obesity "modestly decreases the risk of low-grade and increases the risk of high-grade cancer."

"Our findings should motivate physicians, especially those who care for black men, to address weight loss and maintenance," Dr Barrington advised. "Physicians should explain to their black patients that obesity is uniquely harmful for them in terms of prostate cancer and recommend appropriate prevention strategies."

"The bottom line is that obesity prevention or weight loss is the only known behavior change that can reduce prostate cancer risk, and the benefits are probably more pronounced for black men than non-Hispanic white men," she emphasized.

Obesity as an Explanation?

 
Obesity prevention or weight loss is the only known behavior change that can reduce prostate cancer risk.
 

Black men develop and die from prostate cancer at higher rates than white men. Obesity, which disproportionately affects black men, influences physiologic processes involved in the development of cancer, such as inflammation and insulin sensitivity, and could affect black men differently, the researchers note. Obesity could also affect levels of prostate-specific antigen and genetic risk alleles, which are also more prevalent in black men.

For their study, Dr Barrington and her colleagues analyzed data on 3398 black men and 22,673 white men who participated in the Selenium and Vitamin E Cancer Prevention Trial (SELECT), which was conducted in place in Canada, the United States, and Puerto Rico from 2001 to 2011. The men took either vitamin E or selenium, and were followed for the development of prostate cancer. The trial ended early because of the lack of evidence that these supplements lowered the risk for prostate cancer.

The researchers defined a Gleason score below 7 as low-grade cancer and a Gleason score above 7 as high-grade cancer.

During a follow-up of 5.6 years, the proportion of men who developed prostate cancer was higher in black men than white men (7.9% vs 6.4%). The same pattern was observed for low-grade disease (4.4% vs 4.0%) and high-grade disease (2.6% vs 1.9%).

For men with a BMI below 25 kg/m², the risk for prostate cancer was 28% higher in black men than white men (HR, 1.28; 95% CI, 0.91 - 1.80). That risk increased to 103% for men with a BMI of at least 35 kg/m² (HR, 2.03; 95% CI,1.38 - 2.98; P for trend = .03).

For black men, the risk for prostate cancer was higher for those with a BMI of at least 35 kg/m² than for those with a BMI below 25 kg/m² (hazard ratio [HR], 1.49; 95% confidence interval [CI], 0.95 - 2.34; P for trend = .03). In contrast, for white men, the risk for prostate cancer was lower for those with a BMI of at least 35 kg/m² (HR, 0.80; 95% CI, 0.58 - 1.09; P for trend = .02).

For black men, the risk for low-grade disease was a significant 122% higher for those with a BMI of at least 35 kg/m² than for those with a BMI below 25 kg/m² (HR, 2.22; 95% CI,1.36 - 3.65; P for trend = .005).

For black men, the risk for high-grade disease was 81% higher for those with a BMI of at least 35 kg/m² than for those with a BMI below 25 kg/m² (HR, 1.81; 95% CI, 0.79 - 4.11; P for trend = .02). For white men, the risk was only 33% for those with a BMI of at least 35 kg/m² (HR, 1.33; 95% CI, 0.90 - 1.97; P for trend = .01).

For black men, a BMI of at least 30 kg/m², compared with a BMI below 25 kg/m², meant 414.2 additional cases of prostate cancer per 100,000 person-years.

This study's results "provide a rationale for weight reduction and a target BMI for clinicians" who treat black men, Charles R. Thomas Jr, MD, deputy editor of JAMA Oncology, writes in an accompanying editor's note.

However, he told Medscape Medical News, the results might not be generalizable to the larger population of the United States. Moreover, the trial was not designed to provide recommendations about a specific target BMI that could help reduce prostate cancer risk in black men, he noted.

"For now, it would be reasonable to recommend a healthy lifestyle, such as a balanced diet that includes regular servings of fruit and vegetables along with regular exercise," Dr Thomas emphasized.

The study authors and Dr Thomas have disclosed no relevant financial relationships.

JAMA Oncol. Published online April 16, 2015. Abstract, Editor's note

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