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Cancer risk

Surgery seems associated with increased colorectal cancer risk

The results do not prove that the surgery is the cause of the increased
Dr Jesper Lagergren (Photo credit: Stefan Zimmerman)

Bariatric patients should undergo colonoscopy surveillance after a study found that surgery ‘seems’ to be associated with a long-term increased risk of colon or rectal over time. However, the study authors note that the results do not prove that the surgery is the cause of, and it is not clear why the surgery might be associated to, an elevated risk of colorectal cancer.

"These findings should not be used to guide decisions made by patients or doctors at all until the results are confirmed by other studies," said Dr Jesper Lagergren, the new study's senior author and a professor at both the Karolinska Institute in Stockholm and King's College London.

Although obesity is known to be risk factor several cancers including colorectal, breast and prostate, the study published in the Annals of Surgery, suggests this risk of developing colorectal cancer is even greater for obese people who have undergone weight-loss surgery.

The researchers added that the results should not discourage people from having bariatric surgery as the increased risk for colorectal cancer is not a "negligible risk increase, but it should not be of any major concern for the individual patient since the absolute risk is still low," Lagergren told Reuters Health.

A previous study found that the chances of obesity-related cancers declined following bariatric surgery.

This latest study included 77,111 obese patients from a nationwide retrospective register-based cohort study in Sweden. The long-term risk of colorectal cancer in patients who underwent obesity surgery, and in an obese no surgery cohort, was compared with that of the age-, sex- and calendar year-matched general background population between 1980 and 2009. Obese individuals were stratified into an obesity surgery cohort and an obese no surgery cohort. The standardised incidence ratio (SIR), with 95% confidence interval (CI), was calculated.

The researchers found the risk for colorectal cancer among those who have had bariatric surgery was twice that of patients who did not have surgery.

A total of 15,095 patient received bariatric surgery and 62,016 did not. Seventy patients in the surgery group developed colorectal cancer, rendering (SIR of 1.60 (95% CI 1.25-2.02). The SIR for colorectal cancer increased with length of time after surgery, with a SIR of 2.00 (95% CI 1.48-2.64) after ten years or more.

In contrast, the overall SIR in the obese no surgery cohort (containing 373 colorectal cancers) was 1.26 (95% CI 1.14-1.40) and remained stable with increasing follow-up time.

Lagergren said he did not know why surgery could be associated with an increase risk but hypothesised that could affect gut bacteria and alter future cancer risk or that residual excess weight and weight gain after surgery might be involved.

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