The association between obesity and incidence of total and fatal renal cell carcinoma in two prospective cohorts.

Abstract

414 Background: Recent studies suggest an “obesity paradox” in renal cell carcinoma (RCC), in which obese people are more likely to be diagnosed with RCC, but are less likely to die of the disease. We studied the association of body mass index (BMI) with risk of both total and fatal RCC in two large prospective cohorts. Methods: The Nurses’ Health Study (NHS) consists of 117,097 women followed since 1976, and the Health Professionals Follow-up Study (HPFS) consists of 48,268 men followed since 1986. Height and weight were reported at baseline and updated biennially through 2008, with disease follow-up through 2010. We used multivariable Cox proportional hazards models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for the incidence of both total and fatal pathology-confirmed RCC by BMI immediately prior to diagnosis. Models were adjusted for diabetes, hypertension, smoking, alcohol intake, NSAID use, physical activity, and parity in women. Results: We confirmed 349 cases of RCC, including 103 fatal cases, in NHS, and 226 cases in HPFS, with 46 fatal cases. Compared to women with normal BMI (18.5-24.9 kg/m2) immediately prior to diagnosis, obese women (BMI≥30) had an increased risk of RCC (HR 1.38, 95% CI: 1.03-1.84, p-trend=0.004), adjusting for possible confounders. The HR for fatal RCC was similar but not statistically significant (HR 1.35, 95% CI: 0.79-2.29, p-trend=0.22). Obese men had a non-significantly increased risk of RCC (HR 1.45, 95% CI: 0.96-2.21, p-trend=0.05), with a significantly increased risk of fatal RCC (HR 2.56, 95% CI: 1.11-5.90, p-trend=0.13). Among women, the associations with baseline BMI (1976) were somewhat stronger (HR 1.88, 95% CI: 1.36-2.61, p-trend<0.0001 for total; HR 1.98, 95% CI: 1.07-3.66, p-trend=0.002 for fatal). For men the association with baseline BMI (1986) was weaker for fatal RCC (HR 1.34, 95% CI: 0.50-3.58, p-trend=0.27). Conclusions: Our results support that obesity is a risk factor for RCC incidence and also suggest that it is adversely associated with fatal RCC. These results are stronger for women than for men, though this may be due to the lower number of cases among men.