Obesity Independently Impacts Prostate Cancer Screening
Prostate Cancer PSA Level and BMI
When interpreting prostate cancer screening test results, physicians should consider the impact of a patient's body mass index, regardless of race, according to a new study. Published in the November 15, 2006 issue of CANCER, a peer-reviewed journal of the American Cancer Society, the study found that obese African-American and Caucasian men had lower levels of prostate surface antigen (PSA) and free PSA (fPSA) than men with normal body mass index (BMI), suggesting that an obese man with a slightly elevated PSA may be at higher risk for prostate cancer than a man with normal BMI.
Screening for prostate cancer by measuring PSA levels is now widely available. While credited for detecting small, localized malignancies, an extremely high number of false positive interpretations result in ultimately unnecessary, risky, invasive investigations. For example, high PSA levels may be a malignancy or simply benign prostatic hypertrophy (BPH). Consequently, clinicians still debate its utility in patient care, and researchers look for factors that may affect PSA levels and more specific tests.
Epidemiology evidence shows that obese patients and African-Americans present with more advanced disease. Evidence suggests that body fat, indirectly measured by body mass index (BMI), decreases the amount circulating PSA. Height, too, has been shown to affect percent free PSA (%fPSA).
To further characterize the relationship of PSA, fPSA and %fPSA with BMI, height and race, the investigators interviewed and tested blood from 150 African-Americans and 149 Caucasians.
Jay H. Fowke, Ph.D. of the Vanderbilt University Medical Center in Nashville, and colleagues found PSA and fPSA levels decreased with increasing BMI. This inverse relationship was strongest in men under 60. Race did not effect any association between PSA or %fPSA and BMI. In addition, %fPSA increased with height.
"Whether equal PSA levels in an obese vs. thin man convey the same biologic relevance is unclear," conclude the authors, "but our findings suggest that clinical suspicion might be heightened with a marginally elevated PSA level in an obese person."