Prostate cancer prognosis worse in obese men

NEW YORK (Reuters Health) - Prostate cancer diagnosis tends to be delayed and surgical treatment more difficult in obese men than in lean men, according to two studies published Friday.

The primary reason for the later diagnosis, and consequently poorer prognosis, seems to be that the PSA test used to screen for prostate cancer is "biased" against obese men, according to researchers.

The problem, they explain, may stem from obese men's larger blood volume, which dilutes their PSA levels. High blood levels of PSA -- or prostate specific antigen - can signal the presence of a prostate tumor.

"We know that obese men tend to have lower PSA values than their normal-weight counterparts, possibly caused by larger blood volumes which dilute their readings," Dr. Stephen J. Freedland, who led the studies, said in a written statement.

"Now we know some of the real implications of this -- that these men are at a disadvantage in terms of prognosis compared to normal-weight men."

Freedland, of Duke University Medical Center in Durham, North Carolina, and his colleagues report their findings online in the journal BJU International.

In one study, the researchers looked at the outcomes of nearly 3,400 prostate cancer patients who had undergone surgical removal of the prostate between 1988 and 2007. Some had had their cancer detected by PSA, while the rest had had it discovered during a digital rectal exam.

Overall, Freedland's team found, obese men were more likely to have more-aggressive tumors and to suffer a cancer recurrence after surgery.

However, the link between weight and disease progression was limited to men treated since 2000, when PSA screening had become the norm.

By contrast, obesity had no effect on the risk of progression for cancers detected by digital rectal exam. The findings support the notion that PSA testing, in particular, confers a bias against obese men, according to Freedland.

In the second study, the researchers found that obese prostate cancer patients tend to have a higher rate of "positive surgical margins" after prostate removal -- which means the odds are higher that some tumor cells were left behind.

"The aggressiveness of obese men's tumors, coupled with the fact that they may be more difficult to remove, is like a double whammy for being obese," Dr. Jayakrishnan Jayachandran, another researcher on the studies, said in a statement.

The findings of both studies, according to Freedland, build up the case for developing alternative prostate cancer screening methods for obese men -- or for lowering the PSA threshold for these patients.

"The least we can do is find a way to level the playing field when it comes to diagnostic tools," Freedland said.

SOURCE: BJU International, online August 8, 2008.