Obesity, serum prostate specific antigen and prostate size: implications for prostate cancer detection

Obesity has been associated with lower serum testosterone, theoretically resulting in decreased PSA production. Obesity has also been associated with prostatic enlargement, making the detection of existent cancer more difficult. Together these findings would result in an apparent protective effect of obesity on prostate cancer risk due to technical detection issues unrelated to cancer biology. We examined the association between BMI, and PSA and prostate weight in a cohort of men undergoing RP.

We evaluated the association of BMI with prostate weight and PSA using linear regression, adjusting for patient age at RP, year of RP, race, and pathological stage and grade in 1,414 men treated with RP between 1988 and 2004 at the 5 equal access medical centers that comprise the Shared Equal Access Regional Cancer Hospital Database.

On multivariate analysis increasing BMI was associated with increasing prostate weight but only in men younger than 63 years and not in men 63 years or older (p-trend <0.001 and 0.44, respectively). In men younger than 63 years mean multivariate adjusted prostate weight +/- SE in those with a BMI of less than 25 vs 30 to 34.9 kg/m was 33.8 +/- 1.4 vs 41.4 +/- 1.6 gm. There was no significant association between BMI and preoperative PSA (p-trend = 0.70).

In a cohort of men undergoing RP obesity was associated with larger prostate size but only in younger men. There was no association between BMI and PSA. Assuming equal PSA, the degree of prostatic enlargement observed in younger obese men in this study would be expected to result in a modest decrease in the odds of detecting prostate cancer in a contemporary series of PSA screened men due to the decreased sensitivity of cancer detection related to larger prostate size. Obesity may appear protective for prostate cancer in younger men due to technical issues unrelated to cancer biology.