Anthropometric differences in obese men with biochemical failure after radical retropubic prostatectomy

The effect of obesity on biochemical failure after radical retropubic prostatectomy (RRP) is controversial. The differences in study outcomes may be a result of using body mass index (BMI) rather then direct anthropometric measurements of fat distribution. To investigate these differences, we used endorectal coil MRI (eMRI) data to directly measure fat thicknesses in obese men who underwent RRP.

We performed a retrospective analysis on an RRP database of 1,987 men with available BMI, clinicopathologic characteristics, and biochemical follow-up. Obese men (BMI ≥ 30) were compared with normal weight men (BMI ≤ 25) and overweight men (BMI > 25, < 30) for clinical and pathologic differences and biochemical failure. The eMRI data for 143 obese men were reviewed and the fat thicknesses in the anterior, posterior, and total anteroposterior abdominal diameters were measured and averaged in 3 separate images at and around the midline in the widest segment of the sagittal T2 weighted localizing scans.

Kaplan Meyer curves with log rank analysis revealed a significant difference in biochemical free survival in lean men and overweight men compared with obese men (P = 0.016, P = 0.021). A BMI ≥ 30 did not predict time to biochemical failure on multivariate analysis (HR 1.02, 95% CI 0.67-1.56, P = 0.29). The anterior fat thickness on eMRI in obese men with biochemical failure (n = 21) was significantly smaller than obese men without biochemical failure (n = 122) (35 mm vs. 44 mm, P = 0.003). Calculated percent visceral fat thickness was also significantly larger in obese men with biochemical failure (74% vs.71%, P = 0.02). Subset analysis on patients with extracapsular extension and higher pathologic Gleason scores revealed similar trends in anterior and percent visceral fat thicknesses (P = 0.003, P = 0.02).

Difference in fat distribution may help account for some of the controversy surrounding obesity and prostate cancer. These differences may explain why BMI alone may not adequately predict the influence of obesity on outcomes of prostate cancer treatment.