Objective: Obesity increases the risk of several cancers, but it is uncertain whether weight reduction is followed by any decreased risk. To address this topic, we selected a group of patients representing a substantial weight loss starting at a defined time, ie, patients submitted to obesity surgery. We hypothesized that risk of obesity-related cancer decreases with time after obesity surgery.
Summary Background Data: A nationwide, population-based cohort study of obesity surgery in 1980–2006 as registered in the Swedish Patient Register. New cancers were identified through the Swedish Cancer Register. Cohort members’ observed total number of overall obesity-related cancers and groups of obesity-related cancer (breast, prostate, colorectal, endome-trial, kidney) were divided by the expected numbers, representing the baseline risk, thus calculating standardized incidence ratios (SIRs) with 95% confidence intervals (CIs). Time trends of SIR after obesity surgery were the main outcome measure.
Results: Among a total of 13,123 obesity surgery patients, contributing with 125,049 person-years of follow-up, 296 new cases of obesity-related cancer were identified. There was no overall decrease in SIR of obesity-related cancer with increased time after obesity surgery (P for trend 0.40). Similarly, no statistically significant trends with follow-up time were found for cancer of the breast (P = 0.60), prostate (P = 0.34), endometrium (P = 0.83), or kidney (P = 0.42), while the risk of colorectal cancer increased with time (P for trend 0.01) after obesity surgery.
Conclusions: The weight reduction following obesity surgery might not be entailed by a decreased risk of obesity-related cancer with increasing follow-up time as compared with the baseline risk.