Obesity a competing risk factor in some prostate cancer patients

Washington-When clinicians engage men in discussions of treatment for prostate cancer, they should keep in mind the very real impact of obesity on the man's overall prognosis-a risk that for some men may be more significant than that presented by the malignancy, say researchers from the University of North Carolina, Chapel Hill.

Using data drawn from two large, well-known cohort studies, Stephen McKim, MD, and colleagues calculated the probability of death in 15 years for men with a variety of body mass indices and at various age levels. They compared those data with estimates of 15-year disease-specific mortality by Gleason grade for men whose localized prostate cancer was managed conservatively.

"What we found, in practical terms, is that patients with obesity who have low-grade disease may benefit more in the long term from addressing their obesity rather than their prostate cancer," said Dr. McKim, a urology resident working with Raj S. Pruthi, MD, and colleagues. "At the very least, our study suggests that the potential role of obesity as a competing risk factor should be acknowledged."

Not surprisingly, mortality increased at higher BMI levels and at higher Gleason grades. Patients with Gleason grade ≤6 cancer exhibited lower prostate cancer mortality rates than other causes at each BMI level. On the other hand, men with Gleason 8-10 cancers had higher mortality from cancer at most ages and BMI levels, except for the oldest and most obese patients.

"As men got older, the more obese patients began to have all-cause mortality rates associated with their obesity that increased and overtook the prostate cancer-specific mortality rates," Dr. McKim said at the 2010 American College of Surgeons Clinical Congress in Washington.

The authors' conclusion, then, was that for men at Gleason ≤6 or Gleason 8-10, BMI should have little if any impact on treatment decisions, except in the cases of the oldest and most obese men. As for patients with Gleason 7 disease, they wrote that "the 15-year mortality associated with significant obesity can exceed the disease-specific mortality with prostate cancer."

Like many urologists, Dr. McKim and colleagues noticed that many of their prostate cancer patients also presented with multiple concurrent comorbidities-including obesity-that could be important when making treatment decisions.

"We know that obesity itself can have a significant effect on a patient's life and mortality, so we were interested to know to what degree this compared with the effect of prostate cancer. That is, to what degree could obesity be a competing risk factor in men diagnosed with prostate cancer?" said Dr. McKim, adding that there was some surprise among the investigators to see that men at each age range with low-risk prostate cancer appeared to have a lower risk of dying from the untreated disease than from all causes at each BMI level.