Studies link obesity, severity of prostate cancer

Aggressive tumors seem more likely in fat patients


In men who have prostate cancer, obesity is linked to an increased risk that the cancer will be aggressive and likely to recur after surgery, two studies show.

A connection to obesity might help to explain a racial difference in prostate cancer that has long puzzled researchers: The disease tends to occur at a younger age in black men in the United States than in whites, and it is more aggressive and twice as likely to be fatal.

In the two studies, blacks had higher rates of obesity than whites, a finding that the researchers said might account for much of the racial disparity in the severity of the disease.

The findings are particularly ominous, given that obesity has been increasing for decades and is widely regarded as an epidemic in this country, with more than 30 percent of adults obese and 15 percent of children overweight.

The two new studies, published online last night and scheduled for the Feb. 1 issue of The Journal of Clinical Oncology, are the first to examine obesity's relation to the recurrence of prostate cancer after surgery. Because all the men studied had prostate cancer, the findings apply only to its severity and tendency to recur, and do not indicate whether obesity increases a man's risk of developing the disease.

Although more research is needed to find out for sure whether obesity makes prostate cancer worse, the authors of the studies recommend that all men try to control their weight, whether or not they have had the cancer.

By maintaining a normal weight, men who have had the cancer might reduce the risk of recurrence, and those without cancer might reduce the risk that prostate tumors will be aggressive if they do occur.

"The message is probably more important in men who haven't yet developed prostate cancer," said Dr. Christopher L. Amling, an author of both studies and an assistant professor in the urology department at the Naval Medical Center in San Diego. "We don't know that modifying body weight after you develop an aggressive prostate cancer will change that. It might be too late."

Even if weight turns out not to have a role, obesity is harmful in other ways, and most men will be healthier if they can maintain a normal weight, the researchers said.

"When you look at the statistics, a man who is diagnosed with prostate cancer is more likely to die of heart disease than prostate cancer," said Dr. Stephen J. Freedland, an author of one of the studies and a urologist and clinical instructor in medicine at Johns Hopkins.

"In that sense, trying to lose weight with a healthy diet, not a crash diet, and trying to increase exercise is something they should consider. It's good for the heart. Whether it impacts prostate cancer, we'll see."

The findings have broad implications. In 2003, there were expected to be 220,900 new cases of prostate cancer in the United States and 28,900 deaths. About 1.8 million men are living with the disease. An editorial accompanying the new studies said the findings were provocative and potentially important because obesity is increasing worldwide and "may be one of the few modifiable risk factors for prostate cancer."

Both studies focused on men who had had surgery to remove cancerous prostate glands.

Recurrence was defined as a positive finding on a blood test for a substance called prostate specific antigen, or PSA. After the prostate is removed, PSA should be undetectable; measurable levels usually mean the cancer has recurred. Early recurrence and rapid rise after surgery have been linked to increased death rates.

"This doesn't mean that every obese man will fail or that every non-obese man will do great," Freedland said. "But on average, obese men seem to do worse."

It is not certain why obesity should be linked to more aggressive types of prostate cancer, but the researchers suggest that substances stored in body fat might promote tumor growth. The stored substances include hormones and growth factors.

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