Body mass index as a predictor of prostate cancer: development versus detection on biopsy.

OBJECTIVES: To determine whether obesity is biologically associated with an increased risk of prostate cancer development, especially aggressive disease and to explore whether a bias may exist in our ability to detect these cancers in obese patients.
METHODS: We evaluated the association of body mass index (BMI) with prostate cancer, biopsy Gleason sum, and amount of cancer using logistic and linear regression analyses adjusting for age at biopsy, race, prostate-specific antigen level, digital rectal examination findings, and prostate volume among 787 consecutive men undergoing prostate biopsy between 1998 and 2002 at an equal-access medical center.
RESULTS: Men with a higher BMI were younger (P < 0.001), had lower prostate-specific antigen concentrations (P = 0.02), fewer abnormal digital rectal examination findings (P = 0.02), and larger prostate volumes (P < 0.001). After adjusting for age, no overall association was found between BMI and the odds of being diagnosed with cancer (P trend = 0.89), although overweight and mild obesity were inversely associated with the diagnosis of cancer. After multivariable adjustment, a higher BMI was associated with an increased odds of being diagnosed with prostate cancer (P trend = 0.007). Among men diagnosed with cancer, and after multivariable adjustment, a higher BMI was associated with a similar percentage of biopsy tissue with cancer (P trend = 0.23), but with greater odds of a high Gleason sum (P trend = 0.004).
CONCLUSIONS: After taking into account the clinical characteristics that influence the likelihood of finding an existent cancer, a higher BMI was positively associated with being diagnosed with prostate cancer. Also, among the men with cancer, a higher BMI increased the odds of high-grade disease. These findings suggest that obesity may be biologically associated with prostate cancer development and, in particular, with high-grade disease.