Body mass index (BMI) has been associated with worse outcomes in several solid malignancies. We aimed to evaluate the association between BMI and oncological outcomes in patients treated with radical cystectomy (RC) for muscle-invasive urothelial carcinoma of the bladder (UCB).

We retrospectively reviewed 701 consecutive patients treated with RC and pelvic lymphadenectomy for UCB at our institution between 1995 and 2011. Univariable and multivariable Cox regression models investigated the association of BMI with disease recurrence and cancer-specific mortality. BMI was analyzed as both continuous and categorical variable (<25 vs. 25-29 vs. ≥30 kg/m(2)).

From the 701 patients, 275 (39.2 %) had a BMI < 25 kg/m(2), 280 (39.9 %) had a BMI between 25 and 29.9 kg/m(2), and 146 (20.9 %) had a BMI ⩾ 30 kg/m(2). Within a median follow-up of 45 months (IQR 23-75), 163 patients (23.3 %) experienced a disease recurrence and 127 (18.1 %) died from the disease. In univariable analyses, BMI ⩾ 30 kg/m(2) was associated with a higher risk of disease recurrence and cancer-specific mortality (both p values <0.01). In multivariable analyses that adjusted for the effects of standard clinicopathological features, BMI ⩾ 30 kg/m(2) was associated with both higher risks of disease recurrence (HR 1.58; 95 % CI 1.06-2.34, p = 0.02) and cancer-specific mortality (HR 1.58; 95 % CI 1.01-2.48; p = 0.04).

Obesity was independently associated with higher risks of disease recurrence and cancer-specific mortality in patients treated with RC for muscle-invasive UCB. BMI is a modifiable feature that may have significant individual and public health implications in patients with muscle-invasive UCB.