Obesity may affect PSA screening for prostate cancer

Men with BMI of 35 or higher had PSA concentrations 11% to 21% lower than normal-weight men.

Issue: January 1, 2008

Decreased prostate-specific antigen concentration in men with higher BMI may be caused by hemodilution, according to a report in the Journal of the American Medical Association.

“Our study suggests that we may be failing to detect prostate cancer early in obese men because PSA is diluted due to increased plasma volume,” Lionel L. Bañez, MD, a research fellow in the division of urologic surgery at Duke University Medical Center, told Hem/Onc Today.

The study included about 14,000 men who underwent radical prostatectomy for prostate cancer between 1988 and 2006. Researchers collected data from the Shared Equal Access Regional Cancer Hospital (n=1,373), the Duke Prostate Center (n=1,974) and Johns Hopkins Hospital (n=10,287). The aim was to find the link between PSA concentration and hemodilution in obese men with prostate cancer.

“Our study indicates that it may be time to rethink accepted PSA cut off values, particularly in obese men,” Bañez said.

Serum PSA levels

Multivariate linear regression was used to analyze the associations among BMI and serum PSA concentration, plasma volume and PSA mass. The researchers also modified their study for cancer-specific variables due to the possibility that increased serum PSA values could be a result of widespread prostate cancer.

The researchers reported that in all three groups, higher BMI was related to higher plasma volume (P<.001) and lower PSA concentrations (P<.02). With increasing BMI, there was no significant change in PSA mass in the SEARCH or Duke groups. Higher BMI was related to increased PSA mass in the Johns Hopkins group (P<.001) but was mainly caused by a lower PSA mass in normal-weight men. Once the researchers excluded normal-weight men, there was no major connection between PSA mass and BMI (P=.13).

“We found that men who were excessively obese had PSA values 11% to 21% lower than normal-weight men. Thus, it would be reasonable to recommend lowering the PSA cut-off point by 15% to 20% when managing an obese patient and deciding whether or not a prostate biopsy is indicated,” Bañez said.

The researchers concluded that in these groups, hemodilution may be responsible for lower serum PSA concentrations in obese men with prostate cancer due to the link between increased BMI and higher plasma volume.

“Physicians need to take increased body weight into consideration when interpreting PSA results in obese men. Failure to do so may lead to a large number of missed cancers,” Bañez said.

The researchers wrote that the link found between hemodilution and PSA concentration should be further examined in screened populations in future studies.

“Other bloodborne disease markers may also be falsely diluted due to increased plasma volume, which can negatively affect diagnosis and management of obese patients. Studies aimed at investigating this phenomenon in other diseases should be pursued,” Bañez said. – by Stacey L. Adams

Editor’s note: The next step in evaluating these findings would be to confirm these data in a prospective study and to show that obesity does reduce the ability to detect prostate cancer through PSA screening. Ultimately, as pointed out by the authors, the lack of category-I evidence to show that PSA screening prevents death from prostate cancer somewhat reduces the effect of these findings. In addition, data suggest that a change in PSA, as well as the absolute PSA level, are important parameters, and these data do not suggest that a change in PSA would be confounded by obesity. – Donald L. Trump, MD

For more information:

Bañez L, Hamilton R, Partin A, et al. Obesity-related plasma hemodilution and PSA concentration among men with prostate cancer. JAMA. 2007;298:2275-2280.