A Systematic Review and Meta-Analysis of the Significance of Body Mass Index on Kidney Cancer Outcomes.

ABSTRACT

PURPOSE: Obesity is a well-known risk factor for kidney cancer incidence. However, a number of studies have demonstrated more favorable kidney cancer prognosis in patients with elevated body mass index conferring a survival advantage, termed the "obesity paradox." We aimed to evaluate the association between body mass index and kidney cancer outcomes (progression-free survival, cancer specific survival and overall survival). MATERIALS AND METHODS: A computerized systematic search of Medline®, Embase®, ProQuest®, PubMed® and Google Scholar™ for literature published in English was performed between its inception and December 2018, and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were used for reporting. RESULTS: Overall, 34 publications comprising a total of 50,717 patients were included in the analysis. The majority assessed the association between body mass index and cancer specific survival. Overweight and obese patients were associated with improved cancer specific survival compared to patients with normal body mass index (HR 0.85, 95% CI 0.79-0.93). A similar trend was demonstrated for progression-free survival (HR 0.68, 95% CI 0.59-0.78) and overall survival (HR 0.66, 95% CI 0.55-0.79). On the contrary, the underweight group was associated with inferior cancer specific survival (HR 2.16, 95% CI 1.15-4.04). Main drawbacks limiting the interpretation were the retrospective design in the majority of studies, heterogeneity in study population, body mass index classification and covariates in multivariate analysis. CONCLUSIONS: This is the largest systematic review evaluating the potential phenomenon of the obesity paradox in kidney cancer outcomes. It demonstrated a favorable effect of body mass index on kidney cancer outcomes. However, due to significant heterogeneity of studies, multicenter prospective studies and further research on the fundamental biological mechanisms are warranted to confirm the significance of body mass index on kidney cancer prognosis.