Abstract Background Obesity may be associated with increased risk of recurrence and progression in patients with non‐muscle invasive bladder cancer (NMIBC), but evidence is limited and inconsistent. We examined the associations of body mass index (BMI), waist circumference, and waist‐to‐hip ratio (WHR) with risk of recurrence and progression among patients with NMIBC. Methods This prospective study included 1029 patients diagnosed with primary NMIBC between 2014 and 2017. Patients reported weight 2 years before diagnosis at baseline, and weight, waist and hip circumference at 3 months postdiagnosis. Associations were quantified using Cox proportional hazard analyses, adjusted for clinical and lifestyle characteristics. Results More than half of patients were overweight (49%) or obese (19%) after diagnosis. During a median follow‐up time of 3.6 years, 371 patients developed ≥1 recurrence and 53 experienced progression. No associations with recurrence were observed for BMI (HRper 5 kg/m2 0.94; 95% CI 0.82, 1.07), waist circumference (HRper 10 cm 0.95; 95% CI 0.86, 1.05), or WHR (HRper 0.1 unit 0.90; 95% CI 0.76, 1.06). In contrast, higher BMI was associated with a 40% increased risk of progression, with only the 2‐year prediagnosis association reaching statistical significance (HRper 5 kg/m2 1.42; 95% CI 1.09, 1.84). No associations for pre‐to‐postdiagnosis weight change were found. Conclusion General and abdominal obesity were not associated with recurrence risk among patients with NMIBC, but might be associated with increased risk of progression. Studies with sufficient sample size to stratify by tumor stage and treatment are needed to better understand whether and how obesity could influence prognosis.
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