"We found that overweight men were three times more likely to have their cancer spread," says Christopher J. Keto, MD, a urological oncology postdoctoral associate at Duke University Medical Center, Durham, N.C.
"Obese men were five times more likely than normal-weight men to have their cancer spread," he tells WebMD.
The study was presented at the annual meeting of the American Urological Association in Washington, D.C.
The findings are consistent with previous research that showed a link between obesity and poorer outcomes in prostate cancer patients.
About 217,730 new cases of prostate cancer were diagnosed in 2010, according to the American Cancer Society. About 32,000 men died of the disease last year.
Tracking the Spread of Cancer
Keto and colleagues focused on 287 men who had removal of their prostate gland after the cancer diagnosis. ''All these men had a radical prostatectomy and their cancer came back," Keto says.
Next, the study participants received a treatment known as androgen deprivation therapy (ADT).
The goal of this therapy, Keto says, is to reduce testosterone levels, which can fuel prostate cancer cell growth.
"We know, in general, obesity is a bad thing when it comes to prostate cancer," he says. But "no study out there has looked at how obesity plays into the effect with secondary treatment."
Men in the study had a median body mass index (BMI) of 28.3, Keto says. A BMI of 18.5 to 24.9 is considered normal weight. A BMI of 25 to under 30 is overweight, and a BMI of 30 or above is obese.
"Thirty-five percent of the men in our study had a BMI greater than 30, and 42% had a BMI of 25 to 30," Keto says. "So, 77% of the entire group was either overweight or obese."
The researchers followed the men for a median of 52 months after they started the additional therapy and more than six years after they had the surgery. The higher BMIs were linked with an increased risk of the cancer spreading, the researchers found.
The average age for the overweight and obese men was 65, Keto says. The normal-weight men were on average 67.
Keto says he can't explain exactly why the obese and overweight men with prostate cancer do worse.
"Obese man may not be receiving an adequate dose of the ADT," he says.
Obesity is also linked with increased levels of a number of hormones linked to both obesity and prostate cancer, he says.
Obesity and Prostate Cancer
The study findings build on similar research by Alan Kristal, DrPH, associate head of the cancer prevention program at Seattle's Fred Hutchinson Cancer Research Center and professor of epidemiology at the University of Washington School of Public Health and Community Medicine.
In a study published in the journal Cancer in 2007, Kristal found that obesity more than doubled the odds of prostate cancer death among newly diagnosed men.
He reviewed the new study for WebMD. "It's a very small study," he says. "Nevertheless, it's consistent with other research studies that have found an association with obesity and poor prostate cancer outcome."
He, too, speculates that inflammation associated with obesity may promote the growth of prostate cancer cells.
In his view, the findings are just another reason to control weight as you age.