Obesity portends prostate cancer return, progression

Houston-Obesity has emerged as a potent predictor of whether localized prostate cancer will recur or progress.

Researchers at the University of Texas M.D. Anderson Cancer Center have found that obesity at the time of diagnosis is an independent predictor for recurrence and progression following radiation therapy. This finding mirrors similar results reported in 2005 for prostatectomy patients.

"We know that clinical and pathological factors play a role in predicting how a man will fare over the long term," said Sara Strom, PhD, associate professor of epidemiology at M.D. Anderson and lead author on both studies. "We are investigating other factors that may also influence patient outcome. We found that obesity is an independent prognosticative factor that affects the progression of the disease up to the development of metastases."

Dr. Strom studied 873 M.D. Anderson prostate cancer patients diagnosed between 1988 and 2001 who received full-dose external beam radiotherapy for localized disease. Patients with a body mass index of 18.5 to 24.9 were classified as being of normal weight; BMI 25 to 29.9, as overweight; BMI 30.0 to 34.9, as mildly obese; and BMI of 35 or above, as moderately to severely obese.

The retrospective study found that men who were moderately or severely obese at the time of diagnosis had a 99% increased risk for biochemical failure, defined as rising PSA. Moderately or severely obese patients were also at 66% greater risk for recurrence of a local tumor or metastases than were normal-weight patients.

"We found that weight gain over time is the biggest factor, more important than absolute BMI at the time of diagnosis," Dr. Strom said. "That presents a real problem because so many men gain weight as they age."

The study also found that obese men tend to be diagnosed with prostate cancer at an earlier age. Men who were moderately to severely obese had a mean age of 65 years at diagnosis. That compares with 67.1 years for men who were mildly obese, 68 years for overweight men, and 69.3 years for normal-weight men.

The impact of increasing obesity on cancer progression is similar to the findings of the 2005 report on obesity in prostatectomy patients. That study found a positive association between increased BMI and biochemical failure. Researchers also found that obesity at age 40 years and weight gain over time were strong predictors of biochemical failure.

Regardless of age, obesity has been associated with changes to sex steroids, leptin, insulin, and insulin-like growth factor (IGF-1) pathways, Dr. Strom said. In addition, it has been associated with lower testosterone levels and more advanced prostate cancer. Obesity also boosts insulin and IGF-1 levels, both of which have been associated with more advanced disease.

Data suggest that physicians should "be aware that patients who are obese could be at greater risk," Dr. Strom advised. "Put that into the equation in determining the course of future treatment."

If obesity is associated with worse outcomes, could losing weight after diagnosis help improve the odds for a more favorable outcome? No data currently are available, Dr. Strom said. But because losing excess weight is generally beneficial to health, it would not be unreasonable to suggest weight loss as one course of action for prostate cancer.