Associating the risk of three urinary cancers with obesity and overweight: an overview with evidence mapping of systematic reviews

BACKGROUND: The relationship between cancer with overweight and obesity has been extensively reported. However, the association between urinary cancers with these risk factors remains unclear, with existing reports showing conflicting findings. The current review, therefore, sought to clarify the latter association by assessing the methodological and reporting quality of existing systematic reviews on the subject. METHODS: We first screened PubMed, EMBASE, and Cochrane Library databases for relevant literature and subjected the resulting articles to meta-analysis. We adopted the AMSTAR-2 and PRISMA checklists for assessing methodological and reporting quality, respectively, then performed meta-analyses to determine the relationship between incidence and mortality of three types of urinary cancers with obesity and overweight. Indirect comparisons were also done across subgroups. RESULTS: All systematic reviews (SRs) were of critically low methodological quality. Seventeen SRs had minimal reporting flaws, and 11 SRs had minor reporting flaws. We found an association between obesity with an incidence of kidney (RR = 1.68, 95% CI 1.47–1.92), bladder (RR = 1.1, 95% CI 1.07–1.13), and prostate (RR = 1.02, 95% CI 0.91, 1.13) cancers. Similarly, overweight was associated with the incidence of the three types of cancer, recording RR values of 1.37 (95% CI 1.26–1.48), 1.07 (95% CI 1.03–1.1), and 1 (95% CI 0.93, 1.07) for kidney, bladder, and prostate cancers, respectively. With regard to the dose analysis, the RR of BMI (per 5 kg/m(2) increase) was associated with kidney (RR = 1.24, 95% CI 1.2–1.28), bladder (RR = 1.03, 95% CI 1.02–1.05), and prostate (RR = 1.02, 95% CI 1.01, 1.03) cancers. CONCLUSIONS: This comprehensive quantitative analysis provides an affirmation that overweight and obesity are strong risk factors for kidney cancer, owing to a strong association between them. Conversely, a weak association between overweight and obesity with bladder and prostate cancers confirms their status as mild risk factors for the 2 types of cancer. But due to the low quality of included SRs, the results need to be interpreted with caution. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42019119459 SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13643-021-01606-8.