Obesity surgery and risk of colorectal and other obesity-related cancers: An English population-based cohort study.

Background: The association between obesity surgery (OS) and cancer risk remains unclear. We investigated this association across the English National Health Service. A population-based Swedish study has previously suggested that OS may increase the risk of developing colorectal cancer (CRC).
Methods: A retrospective observational study of individuals who underwent OS (surgery cohort) or diagnosed with obesity, but had no OS (no-surgery cohort) (1997-2013) were identified using Hospital Episode Statistics. Subsequent diagnosis of CRC, breast, endometrial, kidney and lung cancer, as well as time 'at risk', were determined by linkage to National Cancer Registration & Analysis Service and Office of National Statistics data, respectively. Standardised incidence ratios (SIR) in relation to OS were calculated.
Results: 1 002 607 obese patients were identified, of whom 3.9% (n = 39 747) underwent OS. In the no-surgery obese population, 3 237 developed CRC (SIR 1.12 [95% CI 1.08-1.16]). In those who underwent OS, 43 developed CRC (SIR 1.26 [95% CI 0.92-1.71]). The OS cohort demonstrated decreased breast cancer risk (SIR 0.76 [95% CI 0.62-0.92]), unlike the no surgery cohort (SIR 1.08 [95% CI 1.04-1.11]). Increased risk of endometrial and kidney cancer was observed in surgery and no-surgery cohorts.
Conclusions: CRC risk is increased in individuals diagnosed as obese. Prior obesity surgery was not associated with an increased CRC risk. However, the OS population was small, with limited follow-up. Risk of breast cancer after OS is reduced compared with the obese no-surgery population, while the risk of endometrial and kidney cancers remained elevated after OS.
(Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)