The risk for colon cancer may be higher among patients who have had bariatric surgery, according to study published in the International Journal of Cancer.

Obesity is a well-established risk factor for colorectal cancer (CRC); however, previous studies have found that patients who have had bariatric surgery are at increased risk for this disease. The objective of this study was to determine whether the risk for colon and/or rectal cancer increases over time following bariatric surgery.

In this study, data from the Nordic Obesity Surgery Cohort was used to analyze the risk for CRC after bariatric surgery in patients aged 18 or older with a recorded diagnosis of obesity. The study period lasted from January 1980 to December 2015. The 2 study outcomes were colon cancer and rectal cancer, which were identified from codes and corresponding variables in national cancer registers.

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Researchers used standardized incidence ratios (SIR) and 95% CI to compare the incidence of colon cancer and rectal cancer in patients diagnosed with obesity who had and had not undergone bariatric surgery with the incidence in the corresponding background population. Multivariable Cox regression was used to compare the risk for colon cancer and rectal cancer in patients who had undergone bariatric surgery with that among obese patients who had not had surgery. Researchers used hazard ratios (HR) with 95% CI adjusted for confounders such as diabetes, smoking, heavy alcohol use, and inflammatory bowel disease.

Results revealed that among the 502,772 patients in this cohort who were diagnosed with obesity, 9.9% (n=49,931) had undergone bariatric surgery. Gastric bypass surgery was the most prevalent type of bariatric surgery received (72.5%). Of those who had bariatric surgery, 0.3% (n=155) developed colon or rectal cancer during follow-up, compared with 0.6% (n=3158) in the group that did not have bariatric surgery.

Patients who had undergone bariatric surgery were at an overall increased risk for colon cancer compared with the general population (SIR 1.56; 95% CI, 1.28-1.88), which increased approximately twofold after at least 10 years of follow-up. The overall HR of colon cancer in patients who had undergone bariatric surgery compared with those who had not was 1.13 (95% CI, 0.92-1.39) and 1.55 (95% CI, 1.04-2.31) at 10 to 14 years after surgery. There were no statistically significantly increased SIRs observed for rectal cancer.

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This study had several limitations. First, there were possible differences in coding practices for obesity between the countries involved in this study. Second, only patients with a recorded diagnosis of obesity by a healthcare provider were included, which could have diluted the HR considering nondiagnosed patients may also have been at increased risk for colon cancer and rectal cancer. Third, despite the large sample size of the cohort in this study, there was a limited number of patients in the longest follow-up periods.

The researchers concluded that bariatric surgery is strongly associated with an increased risk for colon cancer, though further research may be needed to establish an association between bariatric surgery and an increased risk for rectal cancer.


Tao W, Artama M, von Euler-Chelpin M, et al. Colon and rectal cancer risk after bariatric surgery in a multicountry Nordic cohort study [published online December 3, 2019]. Int J Cancer. doi: 10.1002/ijc.32770

This article originally appeared on Gastroenterology Advisor