Long-term cancer outcomes after bariatric surgery

Abstract

Objective: Obesity is associated with increased cancer risk. Because of the substantial and sustained weight loss following bariatric surgery, postsurgical patients are ideal to study the association of weight loss and cancer.

Methods: Retrospectively (1982-2019), 21,837 bariatric surgery patients (surgery, 1982-2018) were matched 1:1 by age, sex, and BMI with a nonsurgical comparison group. Procedures included gastric bypass, gastric banding, sleeve gastrectomy, and duodenal switch. Primary outcomes included cancer incidence and mortality, stratified by obesity- and non-obesity-related cancers, sex, cancer stage, and procedure.

Results: Bariatric surgery patients had a 25% lower risk of developing any cancers compared with a nonsurgical comparison group (hazard ratio [HR] 0.75; 95% CI 0.69-0.81; p < 0.001). Cancer incidence was lower among female (HR 0.67; 95% CI 0.62-0.74; p < 0.001) but not male surgery patients, with the HR lower for females than for males (p < 0.001). Female surgery patients had a 41% lower risk for obesity-related cancers (i.e., breast, ovarian, uterine, and colon) compared with nonsurgical females (HR 0.59; 95% CI 0.52-0.66; p < 0.001). Cancer mortality was significantly lower after surgery in females (HR 0.53; 95% CI 0.44-0.64; p < 0.001).

Conclusions: Bariatric surgery was associated with lower all-cancer and obesity-related cancer incidence among female patients. Cancer mortality was significantly lower among females in the surgical group versus the nonsurgical group.

Figure 1.

Retrospective study design and exclusions. Diagram indicating the exclusion criteria and number of exclusions for each variable listed. The counts in each line of the boxes represent the number of missing or non-qualifying data points for each variable out of the total records listed in the box above. Each record could have multiple missing values (such as missing age and BMI) and would be counted multiple times for each subject so that the total counts within a box do not add up to the total record count in the preceding box. This allows the counts to represent the amount of missing data for that variable.

Figure 2.

Incident cancer rates^a and hazard ratios^b of bariatric surgery patients compared to non-surgery driver license applicant subjects. HR: hazard ratio; CI: confidence interval; S: surgery group; N: non-surgery group. ^aRates (N): Number of surgical patients/matching controls diagnosed with at least one incident cancer. Rate is defined as incident cancer per 1,000 person years, determined from index date to first incident cancer or follow up date, whichever occurred first. ^bHazard ratio: Includes patients with multiple cancers diagnosed on the same day as one event. Competing risk models were used when subsets of cancers were analyzed. Global test for the proportional hazards assumption for all cancers combined = 0.48

Figure 3.

Rates^a and hazard ratios^b of obesity-associated cancers^c in bariatric surgery patients compared to non-surgery driver license applicant subjects. HR: hazard ratio; CI: confidence interval; S: surgery group; N: non-surgery group. ^aRates (N): Number of surgical patients/matching controls diagnosed with at least one incident cancer. Rate is defined as incident cancer per 1,000 person years, determined from index date to first incident cancer or follow up date, whichever occurred first. Counts less than 11 are required by the Utah Department Health to be reported only as <11. ^bHazard ratio: Includes patients with multiple cancers diagnosed on the same day as one event. ^c See the Methods section for the sources used to determine likely obesity-related cancers. Designation of obesity-related cancers generally has not included premenopausal breast cancer, but it was included in this figure because it was significant in this study.