Obesity Surgery Did Not Increase Risk for Subsequent Colorectal Cancer

A recent observational study showed that although being obese was linked with an increased risk for colorectal cancer, undergoing prior obesity surgery was not associated with increased risk.

However, obesity surgery and the resultant weight loss were linked with a reduced risk of breast cancer, according to the study results reported by Ariadni Aravani, of the University of Leeds, United Kingdom, and colleagues.

Prior research has established that obesity is linked with an increased risk for several kinds of malignancies. Obesity surgery can reduce weight and have associated health benefits, but its effect on colorectal cancer risk is unclear.

A recent meta-analysis of studies looking at this association showed that obesity surgery decreased colorectal cancer risk by 27%. However, all the included studies had limited follow-up and sample size, except one Swedish population-based study that suggested obesity surgery may increase the risk of developing colorectal cancer.

Aravani and colleagues conducted the current study to determine whether obesity surgery has any effect on risk for colorectal cancers. The results were published in Cancer Epidemiology.

The researchers conducted a retrospective observational study looking at more than 1 million people who underwent obesity surgery or were diagnosed with obesity but had no surgery. By linking to the National Cancer Registration and Analysis Service and Office of National Statistics, they were able to link with subsequent diagnoses of colorectal, breast, endometrial, kidney, and lung cancer.

Looking at 1,002,607 obese patients, 3.9% were found to have undergone obesity surgery. Among patients who did not undergo surgery, 3,237 developed colorectal cancer, for a standardized incidence ratio of 1.12. Among these patients, the risk for colorectal disease was higher in men than in women (standardized incidence ratio [SIR] = 1.21 vs 1.02).

Among patients who underwent surgery, 43 developed colorectal cancer, for a SIR of 1.26. In the surgery group, patients who were 50 years of age or older (SIR = 1.47) were at an increased risk for colorectal cancer.

“This study demonstrates that elevated CRC risk continues after obesity surgery, in individuals who underwent obesity surgery over the age of 50 years, an age range at which a significant number of obesity surgery procedures are undertaken,” the researchers wrote.

This increase could “be due to longer exposure to obesity before obesity surgery, something that requires further investigation,” they wrote.

In contrast, the researchers found that patients who had undergone surgery had decreased breast cancer risk (SIR = 0.76) as compared with patients who did not undergo surgery (SIR = 1.08). An increased risk for endometrial and kidney cancer was observed among obese patients regardless of whether or not they underwent surgery.

The researchers acknowledged that the study did not take into account data on body mass index and other risk factors for colorectal cancer.

“Data on BMI after obesity surgery, obtained through linkage to primary care data are required to investigate further the association between OS and CRC risk in the UK,” they wrote.