Surprise finding: Bariatric surgery increases risk of colon cancer

Delhi: Weight-loss surgery (bariatric surgery) may increase the risk for colorectal cancer (CRC) years later, a recent study published in the International Journal of Cancer has found.

The authors found a higher risk of colon cancer in bariatric surgery patients than the general population that increased over time and exceeded the already elevated risk of obese individuals without surgery. Although the cause behind this surprise increase is unknown, the authors speculate changes in the gut microbiome and increased exposure to bile acids to be responsible for this.

Colorectal cancer is the second leading cause of cancer-related death in men and women in the United States. It accounts for 9.7% of all cancer cases and 8.5% of all cancer-related deaths globally and its global burden is expected to rise by 60% between 2012 and 2030.

Obesity is a known risk factor for colorectal cancer but the impact of bariatric surgery on the risk of CRC remains unclear. Many studies have been conducted to establish a link between the two factors, they have yielded contradictory results. While some found an increased risk of colorectal cancer after bariatric surgery, while others have found bariatric surgery to be associated with decreased risk of colorectal cancer.

The study by Wenjing Tao, Karolinska University Hospital, Solna, Sweden, and colleagues aimed to test the hypothesis that the risk of colon and rectal cancer increases over time after bariatric surgery by means of a cohort study with long and complete follow-up based on data from all five Nordic countries.

For the purpose, the researchers compared the incidence of CRC for adults with obesity in Denmark, Finland, Iceland, Norway, or Sweden in 1980 to 2015 who had and had not undergone bariatric surgery.

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Key findings of the study include:

• Among 502,772 cohort participants with an obesity diagnosis, 49,931 (9.9%) underwent bariatric surgery.


• After bariatric surgery, there was an increase in the overall standardized incidence ratio (SIR) of colon cancer (SIR, 1.56), with SIRs higher ≥10 years after surgery.


• In surgical versus nonsurgical participants, the overall hazard ratio (HR) of colon cancer was 1.13 and the HR was 1.5, 10 to 14 years after bariatric surgery.


• The risk for rectal cancer was not significantly increased with bariatric surgery (SIR, 1.14; HR, 1.08); with longer follow-up periods, there was an increase in risk estimates.

"Our study suggests that bariatric surgery is associated with an increased risk of colon cancer, while the support for an increased risk of rectal cancer was weaker," wrote the authors.

"Further research with large cohorts and long follow-up is needed to determine whether bariatric surgery increases the risk of colon and rectal cancer with time after surgery, and if surveillance for such cancer may be warranted in bariatric surgery patients," they concluded.

The study, "Colon and rectal cancer risk after bariatric surgery in a multicountry Nordic cohort study," is published in the International Journal of Cancer.

DOI: https://doi.org/10.1002/ijc.32770