Substantial evidence from clinical trials has established that obesity significantly increases the risk for heart disease and diabetes. More recently, suspicions that obesity is linked to prostate cancer have been supported by a number of investigations, but the nature of the relationship has remained unclear. Now a pair of new studies provide scientists with some important insights that may have an impact on how physicians manage their patients with prostate cancer.

The first study, conducted at the Comprehensive Cancer Center at the University of California, San Francisco, concluded that obesity increases the risk of disease recurrence among men with prostate cancer who have undergone radical prostatectomy (total removal of the prostate gland). The findings suggest that in obese patients the cancer tends to be more aggressive and may progress at a faster clip than in those who aren't obese. They were published in Urology.

"Obesity was an independent predictor of recurrence," said study co-author Christopher Kane, MD, associate professor of urology at the University of California, San Francisco, and chief of urology at the San Francisco VA Hospital. "We found that the more obese a man was, the greater the chances that his cancer would return after the surgery. The chance of recurrence for very obese patients is 70% higher than for others. That's a very significant difference."

The implication is that prostate cancer patients who are obese should probably be followed more closely than patients with similar cancer characteristics who are not obese. That could include regular digital rectal exams, more frequent prostate-specific antigen (PSA) testing, and perhaps setting a lower PSA cutoff point as an indication of recurrence, Kane explained.

The greater risk associated with obesity may be related to technical issues, Kane said. For example, it's more difficult for surgeons to perform a radical prostatectomy in obese patients. However, surgical challenges offer only a partial explanation. In studies where surgeons verified that they had removed all cancer cells during radical prostatectomy, obese patients were still more likely to experience a recurrence of the disease.

"It seems that something biologic is going on, but it's not clear yet what it is," said Kane.

The second study, a multi-center trial coordinated at the Duke University School of Medicine in Durham, NC, found that obese men under the age of 63 tend to have larger prostates, which makes finding tumors more difficult. As a result, there's a real danger of delayed diagnosis, which decreases the chances of a cure and puts patients at greater risk for dying of the disease. The findings appear in the Journal of Urology.

"It's harder to find cancer in larger prostate glands," explained Stephen J. Freedland, MD, assistant professor of urology and member of the Duke Prostate Center at the Duke University School of Medicine. "Consequently, our data suggest that we may be underdiagnosing cancers in younger obese men. That also means that the tumors we do pick up are likely to be at a more advanced stage and perhaps more aggressive, and therefore more difficult to treat."

He recommends that physicians be particularly thorough when examining obese men for prostate cancer, and that obese patients understand their status as high-risk patients. For example, in men with an elevated PSA, even if a biopsy indicates no prostate cancer, a second biopsy may be a reasonable measure to ensure that patient is, indeed, cancer free.

The lower PSA levels typically found in obese men may lead physicians to conclude that a biopsy isn't necessary, Freedland added, and may lead patients toward a false sense of security.

Though some earlier research suggested that obesity actually offered some protection against prostate cancer, substantial evidence refutes any such protective effect. Freedland also observed that because the number of obese men in the United States is growing, understanding what puts them at higher risk might provide researchers with greater insight into cancer biology in general.

"These studies add important information about how obesity relates to prostate cancer, which appears to be yet another serious disease associated with excessive weight," commented Durado Brooks, MD, director of Prostate and Colorectal Cancer for the American Cancer Society. He also emphasized that the studies should alert obese men that a normal digital rectal exam and normal PSA levels may be misleading indicators of true cancer risk, and that they underscore the negative impact that obesity can have on many aspects of life.

Kane echoed those sentiments, saying the studies provide yet more reasons why Americans should follow basic health recommendations to eat fewer calories and get more physical activity.

"It's not just patients with prostate cancer that studies like this should be directed toward," he said. "Patients who are clearly at risk for developing the disease should also take notice of our findings. The central message is yet again that obesity has been identified as an important risk factor for a potentially deadly disease. For all of us, controlling our weight through diet and exercise is important, and we shouldn't have blinders on and just think of prostate cancer. The number one risk of death for American men is heart disease, so anything we can do to reduce that risk that also reduces the risk for prostate cancer is useful."

Citations: "Impact of Obesity on Prostate Cancer Recurrence After Radical Prostatectomy: Data from CaPSURE." Published in the Nov., 2005 Urology (Vol. 66, No. 5: 1060-1065). First author: William W. Bassett, University of California, San Francisco.

"Obesity, Serum Prostate Specific Antigen and Prostate Size: Implications for Prostate Cancer Detection." Published in the Feb. 2006 Journal of Urology (Vol. 175, No. 2: 500-504). First author: Stephen J. Freedland, MD, Duke University School of Medicine.