Obese men with prostate cancer are more likely to have aggressive tumors and disease that recurs after surgery than men who are merely overweight or of normal weight, according to 2 articles published online December 22nd by the Journal of Clinical Oncology.

“The primary role of obesity in prostate cancer is still unclear, but it appears to induce the development of more aggressive tumors,” said Christopher L. Amling, MD, lead author of one of the studies. “I would advise patients to maintain a normal body weight to limit the possibility that they would develop clinically significant, more aggressive prostate tumors.”

Both studies examined the relationship between obesity and recurrence of prostate cancer in large samples of men with localized prostate cancer who had undergone radical prostatectomy. Although obesity rates in the adult U.S. population are similar for African-American and Caucasian men, both studies found that obese patients in the study groups were more likely to be African-American. This finding may help explain an apparent racial difference in disease: African-American men with prostate cancer generally have more aggressive tumors and worse outcomes than Caucasians.

“We suspect that worse outcomes among African-American men with prostate cancer are related to obesity rather than race. If we can target obesity in the African-American community, we may be able to reduce the burden of prostate cancer among black men,” explained the lead author of the second study, Stephen J. Freedland, MD.

Other studies have indicated that obesity influences recurrence of breast cancer in women, but the current studies are the first to investigate the relationship between obesity and recurrence of prostate cancer after surgery.

Dr. Amling’s study involved 3,162 prostate cancer patients, including 19 percent who met the criteria for obesity: a body mass index of 30 kg/m² or higher. Obesity was associated with a higher Gleason score and a higher rate of cancer recurrence as determined by elevated levels of prostate-specific antigen.

Dr. Freedland’s study involved 1,106 patients, including 22 percent who met criteria for mild obesity (body mass index of 30 kg/m² or greater). Men who met criteria for moderate or severe obesity (body mass index of 35 kg/m² or greater) had a higher Gleason score and a higher risk for recurrent disease within 3 years of surgery (latter determined by rising levels of prostate-specific antigen).

Both groups of authors suggest that proteins and hormones stored in body fat --- such as leptin and insulin-like growth factor-1 --- may promote prostate tumor growth in obese men. Also, obese men typically have lower testosterone levels and higher estrogen levels, which may also encourage cancer growth. In addition, diets high in fat may promote tumor growth.

An accompanying editorial commends the studies for presenting a provocative thesis relating obesity with prostate cancer aggressiveness and outcome. “In light of the rising incidence of obesity worldwide, identifying obesity as a risk factor for aggressive prostate cancer is important, since it may be one of the few modifiable risk factors for prostate cancer,” wrote Alfred I. Neugut, MD, PhD. "The number of prostate cancer survivors is steadily increasing, and it will be important to investigate if weight loss and other lifestyle changes can improve prognosis in those already diagnosed with prostate cancer."