Prostate biopsy may be misleading in obese men

In overweight or obese men, prostate biopsy may underestimate the aggressiveness of prostate cancer, research suggests.

"Even if a well-done biopsy shows low-grade cancer in an obese patient, there is still a reasonable likelihood that the patient may have high-grade disease," Dr. Stephen J. Freedland of Duke University Medical Center, Durham, North Carolina commented in a university statement.

A misleading prostate biopsy could lead to inadequate or inappropriate treatment of the cancer, he and colleagues warn in their report, published today in the journal Urology.

The prostate specific antigen, or PSA, is a blood test used to look for early signs of prostate cancer. Men who have a suspicious PSA result often undergo a prostate biopsy, which involves inserting a needle into the prostate to extract tissue for analysis. The results of the biopsy play a critical role in treatment decisions.

Freedland and colleagues analyzed data from 1,113 men who underwent surgical removal of their prostates. The investigators compared the aggressiveness of each patient's cancer, determined by the biopsy tissue, with the actual aggressiveness of disease found by a more extensive microscopic examination of the removed prostate.

Based on inspection of the prostate, the disease of 299 men (27 percent) was upgraded to a worse status and downgraded to a more favorable status in 123 men (11 percent). Disease status was on the mark in 691 men (62 percent).

In analyses that took into consideration the influence of potentially confounding factors, obesity was significantly associated with upgrading of the prostate biopsy results.

Obese men were 89 percent and overweight men 44 percent more likely than normal-weight men to have a more aggressive form of prostate cancer than was suggested by the biopsy.

"We already know it's more difficult to diagnose prostate cancer in obese men because they have lower levels of PSA...and because their larger-sized prostates make it more likely for a biopsy to miss the cancer," Freedland said. "These findings further suggest that we could be missing even more high-grade disease among obese men."

Doctors may need to perform more biopsy samples on obese men, according to Freedland, in order to determine the "true aggressiveness of the prostate cancer and allow treatment to be better tailored to the patients' needs."

SOURCE: Urology, March 2007.