Donat et al also found no correlation with BMI and cancer specific survival in 859 patients who underwent nephrectomy at MSKCC. BMI was not an independent predictor of overall survival between the normal, overweight and obese cohorts. Obese patients did have a higher incidence of conventional cell histology (37%) compared to normal weight patients (24%). Hafron et al investigated 288 patients with a median BMI of 26.98 who underwent cystectomy. In patients with organ-confined bladder cancer, there was no survival difference between normal and obese patients (p=.44).

In terms of cancer incidence BMI does not correlate with incidence of prostate or bladder cancer however has been demonstrated to be directly correlated with incidence of renal cell carcinoma.

Although the current research shows the insignificance of BMI in outcome of most urologic cancers, the influence of BMI in other urologic aspects, such as erectile dysfunction (ED), is more tangible. Kratzik et al evaluated how age, BMI and testosterone affected ED in 675 men. Both age and BMI independently lowered the score on the International Index of Erectile Function (IIEF-5), which measures ED, in a multivariate model. Obese men were 1.952 times more likely to have ED than normal men. Testosterone was not an independent predictor of ED. However, lower testosterone did correlate with a worse score on the IIEF-5, and did predict ED in a univariate model.

Stone disease can also be positively correlated to BMI. Taylor et al associated higher BMI with increased stone formation in both men and women. In a large cohort of 241,623 patients from the Health Professionals Follow-up Study and the Nurses Health Study, 4877 patients had stone disease. Stone formation was more likely to be found in obese patients than normal weight patients (p=0.001). The study suggests that perhaps hyperinsulinemic overweight patients secrete more calcium, or that obese patients produce a more concentrated uric acid, a risk factor for calcium oxalate stones.

In sum, body mass index does not have a profound effect on urologic cancers. Obesity does not create a survival disadvantage for patients undergoing prostatectomy, nephrectomy or cystectomy. However, BMI does significantly impact the urologist in the treatment of erectile dysfunction and stone disease. Perhaps the management of these disorders might include the encouragement of weight lose in a multi-modality approach to treatment.

Written by James M. McKiernan, MD. Presented at the 32nd Winter Urologic Forum - State-of-the-Art in Urology.

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