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An occasional nuisance men endure to check for prostate cancer, the digital rectal exam may have heightened importance for those who are obese.

Researchers at the Duke Cancer Institute and elsewhere have found that the doctors' office exam may be better at detecting advanced prostate tumors in heavy men than in their normal-weight counterparts.

The reason may be that earlier, smaller tumors are not discernable through excessive girth –- a shortcoming made worse by the tendency for PSA screenings to also miss early signals of prostate cancer among obese men.

The findings help explain why prostate cancer is often more lethal among overweight men vs. those of healthy weight.

"This may be why obese men get diagnosed at later stages – it's not getting caught early," said David Chu, MD, urology resident at Duke University and lead author of the study published this month in the journal Prostate Cancer and Prostatic Diseases.

Nearly 241,000 men in the United States will be diagnosed with prostate cancer this year, and obesity has long been considered a risk factor for worse outcomes. With an annual death toll of 34,000, prostate cancer is the second-most lethal malignancy among men after lung cancer, according to the American Cancer Society.

In the current study, researchers at Duke, the Veterans Affairs Medical Center in Durham, N.C., and La Sapienza University of Rome, Italy, analyzed data from 2,794 men undergoing prostate biopsies.

The researchers found that obese men were less likely to have abnormal digital rectal exams than non-obese patients.

But when a mass was suspected, it was as much as three times more likely to be cancer among the heavy-set patients than in the normal-weight men.

"If the tumor is less likely to be diagnosed with a digital rectal exam, it will be larger in size to be palpable, and therefore may be more aggressive when it is discovered," Chu said.

Additionally, the researchers found that the digital rectal exam among obese men actually detected some tumors that were not flagged by prostate-specific antigen (PSA) screening alone.

That finding reconfirmed earlier research at Duke that PSA tests often fail to indicate a potential problem in obese men. In such instances, the PSA protein detected in the test reads normal, but may actually be at an elevated level that is diluted by a bigger mans' additional volume of blood.

As a result, the current study suggest that while an abnormal digital rectal exam may be an important predictor for prostate cancer in normal-weight men, it confers extra significance for obese men.

"The digital rectal exam is a simple and safe procedure to do –- physicians should not neglect to do it -- especially in obese men, specifically because they are at high risk for unfavorable cancer outcomes," said Lionel Bañez, MD, assistant professor of urologic surgery at Duke and senior author of the study.

In addition to Chu and Bañez, study authors included: Cosimo De Nunzio; Leah Gerber; Jean-Alfred Thomas II; Elizabeth E. Calloway; Simone Albisinni; Cagri Senocak; Madeline G. McKeever; Daniel M. Moreira; Andrea Tubaro; Judd W. Moul; and Stephen J. Freedland.

The study was funded by the National Institutes of Health, the Department of Defense and the Duke Division of Urologic Surgery. Authors reported no conflicts of interest.