Extreme body mass index is associated with poor survival outcomes after radical cystectomy: a retrospective cohort study in a Chinese population

Background Body mass index (BMI) has been evidenced to be a significant prognostic factor in multiple cancers. This retrospective study aimed to investigate the association between BMI and survival outcomes after radical cystectomy (RC) in patients with bladder cancer (BCa). Methods Clinical and pathological parameters of patients who were diagnosed with BCa and received RC between 2010 and 2018 were collected. The associations between BMI at surgery and clinicopathological features were examined. The prognostic value of BCa for overall survival (OS) and cancer-specific survival (CSS) was examined using the Kaplan-Meier method and Cox regression models. Results Among the 217 patients enrolled in this study, 13 (6.0%), 121 (55.8%), 60 (27.6%), and 23 (10.6%) had a BMI value of <18.5 kg/m2 (underweight), 18.5-23.9 kg/m2 (normal), 24-27.9 kg/m2 (overweight), and ≥28 kg/m2 (obese), respectively. Underweight and obese patients tended to have poorer survival after RC than normal and overweight patients (P<0.05). Multivariable Cox regression revealed that extreme BMI was an independent predictor of both OS (BMI <18.5 vs. 18.5-27.9 kg/m2, OR =2.675, 95% CI: 1.131-6.327, P=0.025; BMI ≥28 vs. 18.5-27.9 kg/m2, OR =3.693, 95% CI: 1.589-8.583, P=0.002) and CSS (BMI <18.5 vs. 18.5-27.9 kg/m2, OR =3.012, 95% CI: 1.180-7.687, P=0.021; BMI ≥28 vs. 18.5-27.9 kg/m2, OR =3.801, 95% CI: 1.526-9.469, P=0.004), along with tumor stage and urinary diversion type. Conclusions Being underweight or obese is associated with a poor prognosis in patients with BCa undergoing RC. For patients who are preparing to undergo RC for BCa, controlling the BMI index through diet or exercise before surgery may contribute to the surgical curative effect and an improved prognosis.