Bariatric Surgery Lowers Five-Year Cancer Risk in Women, But Not Men

A recent study observed a correlation between bariatric surgery and decreased cancer risk among women over a five-year period—the same association was not observed among men, though.

Obesity is an established risk factor for cancer at more than a dozen sites, including esophagus (adenocarcinoma), gastric cardia, colon, rectum, liver, gallbladder, pancreas, breast (postmenopausal), corpus uteri, ovary, kidney (renal cell), meningioma, thyroid and multiple myeloma.

“Bariatric surgery normally results in substantial and long-lasting weight loss and reduces obesity-related morbidity and mortality. Available studies indicate a 30–50% overall decreased risk of cancer following bariatric surgery,” wrote the study authors. “However, studies on bariatric surgery and specific cancer sites have provided inconsistent results, which might partly be a reflection of the limited number of cancer cases and length of follow-up in these studies.”

National patient registries in Denmark, Finland, Iceland, Norway, and Sweden spanning 1980 through 2012 were queried for adults diagnosed with obesity. Obese adults who underwent bariatric surgery were compared to obese adults who did not undergo surgery for cancer risk. Confounders included age, sex, calendar year, country, length of follow-up, diabetes, chronic obstructive pulmonary disease, and alcohol-related diseases.

Final analysis included 482,572 patients with obesity, of whom 49,096 underwent bariatric surgery. Among women, bariatric surgery led to a decreased overall cancer risk (hazard ratio [HR], 0.86; 95% confidence interval [CI], 0.80 to 0.92), but not among men (HR, 0.98; 95% CI, 0.95 to 1.01); the reduced risk only persisted for the first five years. Specifically, among women, bariatric surgery reduced the risk of breast cancer (HR, 0.81; 95% CI, 0.69 to 0.95), endometrial cancer (HR, 0.69; 95% CI, 0.56 to 0.84), and non-Hodgkin lymphoma (HR, 0.64; 95% CI, 0.42 to 0.97); among men and women, bariatric surgery increased the risk for kidney cancer (HR, 1.44; 95% CI, 1.13 to 1.84).

The study was published in Obesity Surgery.

“The decreased cancer risk following bariatric surgery was only found during the initial five years after surgery. While limited statistical power in the longer follow-up periods might contribute to the lack of significant results, a possible explanation could be that weight loss, which is most substantial during the first post-operative years, has an independent protective effect on cancer,” the researchers speculated. They added, “Furthermore, the type of bariatric procedures performed have changed over time and might contribute to the differential results across follow-up periods; gastric bypass is currently the dominant procedure in the Nordic countries and results in greater weight loss than restrictive procedures that were popular previously. Previous studies have shown a stronger association between gastric bypass and reduced cancer risk than restrictive procedures.”

They concluded by calling for further investigation into the increased kidney cancer risk they observed in the bariatric surgery cohort.