Risk for colon cancer may be increased in patients who have undergone bariatric surgery, while the association between weight-loss surgery and rectal cancer is weaker, according to study results published in International Journal of Cancer.

While previous studies have identified obesity as a risk factor for colorectal cancer, others have reported that bariatric surgery may also increase the risk for the malignancy. The goal of the current study was to examine the association between bariatric surgery and risk for colon and rectal cancer over time.

Information from the population-based Nordic Obesity Surgery Cohort was collected for the analysis. In total, 502,772 patients with obesity from 5 Nordic countries (Denmark, Finland, Iceland, Norway, and Sweden) were included, with 49,931 having undergone bariatric surgery. The researchers explored the incidence of colorectal cancer in patients after bariatric surgery vs in patients with obesity in the background population by calculating standardized incidence ratios (SIRs).

Compared with the general population, patients who had undergone bariatric surgery had a higher overall risk for colon cancer (SIR, 1.56; 95% CI, 1.28-1.88). After ≥10 years of follow-up, risk had increased 2-fold for the group of patients who had undergone bariatric surgery, with a peak at 10 to 14 years after the surgery (SIR, 2.07; 95% CI, 1.36-3.01).


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Risk for rectal cancer was not significantly increased after bariatric surgery (SIR, 1.14; 95% CI, 0.83-1.52), but risk tended to increase with longer follow-up after surgery, with a SIR of 1.62 (95% CI, 0.78-2.98) ≥20 years after surgery.

Risk for colon cancer was increased in patients after bariatric surgery compared with in patients with obesity who did not undergo bariatric surgery (adjusted hazard ratio [HR], 1.13; 95% CI, 0.92-1.39), but this was not statistically significant. A similar trend was evident for rectal cancer (adjusted HR, 1.08; 95% CI, 0.79-1.49). Risk for colon and rectal cancer increased with longer follow-up, as bariatric surgery was associated with increased risks for colon cancer 10 to 14 years after surgery (HR, 1.55; 95% CI, 1.04-2.31) and rectal cancer ≥20 years after surgery (HR, 2.11; 95% CI 1.03-4.32).

The researchers acknowledged several limitations of the study, including possible differences in coding practices for obesity between countries, potential selection bias, residual unmeasured confounders, and a limited number of patients in the longest follow-up periods.

“Our study indicates that bariatric surgery is associated with an increased risk of colon cancer compared to the general population. While no statistically significant result of such increase was found for rectal cancer, the risk estimates seemed to increase with longer follow-up,” wrote the researchers.

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Reference

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