Bariatric surgery cuts obesity-associated cancer, cancer death risks

For individuals with obesity, undergoing weight-loss surgery may be a lifesaver, not only helping avert cancer-related deaths but also preventing the incidence of obesity-associated cancer, according to data from the SPLENDID (Surgical Procedures and Long-term Effectiveness in Neoplastic Disease Incidence and Death) study.

In a cohort of 30,318 patients (median age 46 years, 77 percent female, 73 percent White) with a median body mass index of 45 kg/m², fewer patients who did vs did not undergo bariatric surgery developed obesity-associated cancer (incidence rate, 3.0 vs 4.6 events per 1,000 person-years) and had cancer-related deaths (incidence rate, 0.6 vs 1.2 events per 1,000 person-years). [JAMA  2022;327:2423-2433]

Bariatric surgery led to a significantly lower cumulative 10-year incidence of obesity-associated cancer (2.9 percent vs 4.9 percent; absolute risk difference, 2.0 percent, 95 percent confidence interval [CI], 1.2–2.7) and reduced the risk by 32 percent (adjusted hazard ratio [aHR], 0.68, 95 percent CI, 0.53–0.87; p=0.002).

The same was true for cancer-related mortality, with the cumulative 10-year incidence being lower in the surgery vs no-surgery group (0.8 percent vs 1.4 percent; absolute risk difference, 0.6 percent, 95 percent CI, 0.1–1.0). Bariatric surgery yielded a 48-percent reduction in the risk of such outcome (aHR, 0.52, 95 percent CI, 0.31–0.88; p=0.01).

The findings are in line with prior studies reporting that bariatric surgery was associated with a significant reduction in the risks of different cancer types and cancer-related mortality. [Ann Surg 2019;269:95-101; Obesity 2009;17:796-802; Gynecol Oncol 2017;145:224-229; Br J Surg 2018;105:1650-1657; Gastroenterology 2021;161:171-184.e10; Br J Surg 2022;109:433-438]

However, among all cancer types, endometrial cancer had the strongest association with obesity, the investigators pointed out, adding that endometrial cancer was the only cancer type that had a significantly lower incidence after surgery relative to no surgery in the SPLENDID cohort (aHRs, 0.56 and 0.22, respectively).

“A study in 72 women with severe obesity, for whom endometrial biopsies were examined before and after bariatric surgery, showed a significant reduction in the markers of endometrial proliferation and oncogenic signalling after surgery,” they said. [Int J Cancer 2019;144:641-650]

Payoff of losing pounds

In current practice, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) are the most common bariatric procedures and results in similar extent of weight loss. However, the investigators noted that the two procedures have different physiological effects: a large part of the stomach removed with SG, while the gastrointestinal tract is re-routed with RYGB.

“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,” they said.

A total of 5,053 patients underwent bariatric surgery (RYGB 66 percent; SG 34 percent) and 25,265 did not in SPLENDID. The mean between-group difference in body weight at the 10-year follow-up was 24.8 kg (95 percent CI, 24.6-25.1 kg), which translates to a 19.2-percent (95 percent CI, 19.1–19.4) greater weight loss in the bariatric surgery group.

The investigators called for additional studies to establish the mechanisms responsible for reduced cancer risk after bariatric surgery.

The study was limited by the possibility of residual measured or unmeasured confounders influencing the findings, the small number of incident cancer cases, and the limited generalizability of the data to individuals of other racial and ethnic groups, among others.