Cumulative obesity exposure increases the risk of kidney cancer: a longitudinal nationwide cohort study.

Obesity is one of the most important prognostic factors of kidney cancer. However, little is known regarding the cumulative impacts of obesity on kidney cancer risk. We aimed to analyze the dose- and time-dependent impact of obesity on kidney cancer risk using the Korean National Health Insurance System database. This longitudinal nationwide cohort study used data from the Korean National Health Insurance System database between 2012 and 2013. In total, 3,102,240 participants who received annual health examination more than four times consecutively were included in the final analysis. The primary endpoint was newly diagnosed kidney cancer according to the dose- and time-dependent impact of obesity. Dose-dependent impact was measured using body mass index (BMI) and waist circumference (WC), and time-dependent impact was measured using general and abdominal cumulative obesity exposure (gCOE and aCOE). COE was defined as the number of years since obesity diagnosis during the exposure period. We identified 1,831 participants with newly diagnosed kidney cancer (median follow-up: 4.3 years). The hazard ratios (HRs) for kidney cancer increased significantly alongside BMI and WC. The HRs for kidney cancer increased significantly in the higher gCOE groups ( for trend <0.001) as follows: 1 (1.33, 95% confidence intervals: 1.10-1.60), 2 (1.33, 1.08-1.63), 3 (1.55, 1.30-1.85), and 4 (1.82, 1.64-2.03) years. Similar trends were observed for aCOE ( for trend <0.001) as follows: 1 (1.42, 1.23-1.64), 2 (1.71, 1.46-2.02), 3 (1.76, 1.48-2.08), and 4 (2.11, 1.84-2.42) years. Risks of kidney cancer related to COE were much more pronounced in participants with the following characteristics: younger than 65 years old, male gender, diabetes, hypertension, and dyslipidemia. Longer COE was associated with an increased risk of kidney cancer in the Korean population. Participants with prolonged obesity and metabolic syndrome need active surveillance for kidney cancer.