The newly identified association between obesity and lower prostate-specific antigen levels in men with prostate cancer may be due to dilution of antigen in the higher plasma volumes associated with greater body mass index, according to an article in the November 21 issue of the Journal of the American Medical Association.

Recent evidence had suggested that prostate cancer screening may be adversely affected by increased body mass index, according to background information in the article. Several studies had found that obese men have lower prostate-specific antigen concentrations than non-obese men.
"However, men with higher body mass indices also have larger plasma volumes, which could decrease serum concentrations of soluble tumor markers-a phenomenon known as hemodilution," the authors wrote.

Lionel L. Banez, M.D., of Duke University Medical Center, Durham, NC, and colleagues conducted a study to determine the association between hemodilution and antigen concentration in obese men with prostate cancer.

The analysis included 13,684 men who underwent radical prostatectomy for prostate cancer from 1988 to 2006 and who were included in one of three databases: the Shared Equal Access Regional Cancer Hospital (1,373 patients), Duke Prostate Center (1,974 patients), and Johns Hopkins Hospital (10,287 patients).

The researchers found that higher body mass index was significantly associated with greater plasma volume in all study populations. Men with an index of 35 or greater had 21 percent to 23 percent larger plasma volumes compared with normal-weight men.

After adjusting for multiple clinicopathological variables, higher body mass index was associated with lower pre-operative prostate-specific antigen concentrations in all groups. Men with an index of 35 or greater had 11 percent to 21 percent lower antigen concentrations than normal-weight men.

"In three distinct prostate cancer cohorts, all treated by radical prostatectomy, hemodilution from increased plasma volume may be responsible for the observed decreased prostate-specific antigen concentration in men with higher body mass index. This association needs to be confirmed prospectively in screened populations that include men without prostate cancer," the authors concluded.