Bariatric surgery associated with lower risk of obesity-related cancer

An observational study found significant reductions in a composite outcome of 13 cancers and related mortality in patients with a body mass index of 35 kg/m2 or greater who had bariatric surgery in 2004 to 2017, compared to those who did not undergo surgery for their obesity.

Patients who had bariatric surgery had lower risk of obesity-related cancer than similar patients who did not undergo surgery, a recent observational study found.

The SPLENDID (Surgical Procedures and Long-term Effectiveness in Neoplastic Disease Incidence and Death) study matched patients with a body mass index (BMI) of 35 kg/m2 or greater who had bariatric surgery in 2004 to 2017 (n=5,053) with patients who did not undergo surgery for their obesity (n=25,265). Follow-up ended in February 2021 (median follow-up, 6.1 years). Results were published by JAMA on June 3.

Most patients were White (73%) and female (77%). Their median age was 46 years, and median BMI was 45 kg/m2. At 10 years, the mean between-group difference in body weight was 24.8 kg (95% CI, 24.6 to 25.1 kg), a 19.2% (95% CI, 19.1% to 19.4%) greater weight loss in the bariatric surgery group. Overall, obesity-associated cancer (a composite of 13 cancer types) was diagnosed in 96 surgery patients and 780 control patients (incidence rate, 3.0 vs. 4.6 events per 1,000 person-years). The primary end point of obesity-related cancer and cancer-related mortality was 2.9% (95% CI, 2.2% to 3.6%) in the surgery group and 4.9% (95% CI, 4.5% to 5.3%) in the nonsurgical control group (absolute risk difference, 2.0% [95% CI, 1.2% to 2.7%]; adjusted hazard ratio, 0.68 [95% CI, 0.53 to 0.87]; P=0.002).

The study authors concluded that bariatric surgery was associated with a significantly lower incidence of obesity-associated cancer and cancer-related mortality compared with no surgery. They noted that this appeared to be true for both Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). “Overlap of Kaplan-Meier curves for RYGB and SG suggests that losing weight itself, not procedure-specific physiological changes related to anatomical alterations, could be the principal mechanism for reduced risk of obesity-associated cancer,” the authors wrote.

They also noted that this and other studies show that “substantial weight loss was required to observe a meaningful reduction in the cancer risk in a dose-dependent response” and that “bariatric surgery is the only available treatment that can provide this magnitude and durability of weight loss.”

An accompanying editorial highlighted some limitations, including the risk of confounding and potential selection bias. “Despite adjustments in the statistical modeling and thorough sensitivity analyses, the concern is that people who choose to undergo bariatric surgery are drawn from a different population than those who do not choose to undergo surgery. In addition, extensive lifestyle changes and smoking cessation are required for bariatric surgery candidates,” the editorial said. “The results from the studies that have assessed bariatric surgery and cancer risk are also not generalizable to men or people from all ethnic and racial backgrounds.”