French Study Finds Lower Risk Of Colon Cancer After Bariatric Surgery

Weight-loss operations may reduce the risk for colon cancer in patients with obesity, a French cohort study suggests.

The association of these procedures with colorectal cancer risk has been controversial. A large Scandinavian study recently concluded that obese patients have higher colon cancer risk after weight-loss surgery, but reports from other regions have described the opposite.

This week in JAMA Surgery, French researchers report that patients with obesity who undergo bariatric surgery have "the same risk of colorectal cancer as the general population, whereas for patients with obesity who do not undergo bariatric surgery, the risk is 34% above that of the general population."

Dr. Laurent Bailly of Hopital L'Archet and CHU de Nice and colleagues drew their findings from national health-insurance data on more than 1 million patients with obesity, ages 50 to 75, with no history of colorectal cancer.

"In France, since 2009, a colorectal cancer screening program has been targeting the entire 50- to 75-year-old population covered by the National Health Insurance," Dr. Bailly noted in an email to Reuters Health.

Study participants included 74,131 individuals who had undergone bariatric surgery (mean age, 57.3) and more than 971,000 propensity-matched individuals who had not (mean age, 63.4).

Mean follow-up was 5.7 years for patients who had weight-loss surgery (adjustable gastric banding, sleeve gastrectomy, or gastric bypass) and 5.3 years for the no-surgery group. Overall, 13,052 new colorectal cancers (1.2%) and 63,649 benign colorectal polyps were diagnosed, according to Dr. Bailly's team.

The rate of colorectal cancer was 0.6% with bariatric surgery and 1.3% without it. In the surgery cohort, 428 cases were expected and 423 observed, for a standardized incidence ratio of 1.0 (95% confidence interval, 0.90 to 1.09).

Among patients who didn't have one of these operations, 9,417 cases were expected but 12,629 were observed, for a standardized incidence ratio of 1.34 (95% CI, 1.32 to 1.36).

Propensity-score-matched hazard ratios in comparable operated vs nonoperated groups were 0.68 (95% CI, 0.60 to 0.77) for colorectal cancer and 0.56 (95% CI, 0.53 to 0.59) for benign colorectal polyps.

The incidence of colorectal cancer was 0.5% after gastric bypass, 0.5% after sleeve gastrectomy and 0.7% gastric banding. The incidence of benign polyps followed a similar pattern: 3.1% after gastric bypass, 3.1% after sleeve gastrectomy, and 5.0% after gastric banding.

The authors note, "Our study results were not consistent with the increased risk of colorectal cancer observed after bariatric surgery in studies conducted in Sweden or...England."

But the strengths of their study, they add, include its "population-based design, with (standardized incidence ratios) calculated on matched colorectal cancer incidence among the French general population," and "the long-term follow-up of a large national cohort who underwent these surgical procedures."

Dr. Jesper Lagergren, professor of surgery at Karolinska Institutet and Karolinska University Hospital in Stockholm, coauthored two earlier studies that found an increased risk of colon cancer with bariatric surgery in Scandinavian patients, using a method similar to that used by Dr. Bailly's group. Dr. Lagergren told Reuters Health by email, "A possible reason for the lack of an increased risk of colorectal cancer in the French study was the limited follow-up time after bariatric surgery. The influence of bariatric surgery is likely to be seen only a couple of decades later and the study period in the French study was only up to maximum 9 years."

"Bariatric surgery seems to decrease the risk of mortality in general, including death from cancer, so the potentially increased risk of colorectal cancer should not stop these procedures," Dr. Lagergren continued. "Thus, doctors can continue referring patients for bariatric surgery. However, the potentially increased risk of colorectal cancer (if proven true in further research) should not be dismissed, because it could justify colonoscopy in these patients to detect any colorectal cancer before becoming advanced and incurable. Yet, the association between bariatric surgery and colorectal cancer remains uncertain."

—Nancy Lapid

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