Body Mass Index, Diet-Related Factors, and Bladder Cancer Prognosis: A Systematic Review and Meta-Analysis

Background: Urologists are frequently confronted with questions of urinary bladder cancer (UBC) patients about what they can do to improve their prognosis. Unfortunately, it is largely unknown which lifestyle factors can influence prognosis. Objective: To systematically review the available evidence on the association between body mass index (BMI), diet, dietary supplements, and physical activity and UBC prognosis. Methods: We searched PubMed and Embase up to May 2017. We included thirty-one articles reporting on observational and randomized controlled trials investigating BMI, diet and dietary supplements in relation to recurrence, progression, cancer-specific or all-cause mortality in UBC patients. Results: In non-muscle invasive bladder cancer (NMIBC) patients, both overweight (3 studies, pooled hazard ratio (HR) 1.29, 95% CI 1.05-1.58, I-2 = 0%) as well as obesity (3 studies, pooled HR 1.82, 95% CI 1.12-2.95, I-2 = 79%) were associated with increased risk of recurrence when compared to normal weight. No association of BMI with risk of progression was found. Results for BMI and prognosis in muscle-invasive or in all stages series were inconsistent. Observational studies on diet and randomized controlled trials with dietary supplements showed inconsistent results. No studies on physical activity and UBC prognosis have been published to date. Conclusions: Evidence for an association of lifestyle factors with UBC prognosis is limited, with some evidence for an association of BMI with risk of recurrence in NMIBC. Well-designed, prospective studies are needed to develop evidencebased guidelines on this topic.