Importance: Obesity is a cancer risk factor, and bariatric surgery in patients with obesity is associated with reduced cancer risk. However, evidence of an association among obesity, bariatric surgery, and skin cancer, including melanoma, is limited.
Objective: To investigate the association of bariatric surgery with skin cancer (squamous cell carcinoma and melanoma) and melanoma incidence.
Design, setting, and participants: This nonrandomized controlled trial, the Swedish Obese Subjects (SOS) study, is ongoing at 25 surgical departments and 480 primary health care centers in Sweden and was designed to examine outcomes after bariatric surgery. The study included 2007 patients with obesity who underwent bariatric surgery and 2040 contemporaneously matched controls who received conventional obesity treatment. Patients were enrolled between September 1, 1987, and January 31, 2001. Data analysis was performed from June 29, 2018, to November 22, 2018.
Interventions: Patients in the surgery group underwent gastric bypass (n = 266), banding (n = 376), or vertical banded gastroplasty (n = 1365). The control group (n = 2040) received the customary treatment for obesity at their primary health care centers.
Main outcomes and measures: The SOS study was cross-linked to the Swedish National Cancer Registry, the Cause of Death Registry, and the Registry of the Total Population for data on cancer incidence, death, and emigration.
Results: The study included 4047 participants (mean [SD] age, 47.9 [6.1] years; 2867 [70.8%] female). Information on cancer events was available for 4042 patients. The study found that bariatric surgery was associated with a markedly reduced risk of melanoma (adjusted subhazard ratio, 0.43; 95% CI, 0.21-0.87; P = .02; median follow-up, 18.1 years) and risk of skin cancer in general (adjusted subhazard ratio, 0.59; 95% CI, 0.35-0.99; P = .047). The skin cancer risk reduction was not associated with baseline body mass index or weight; insulin, glucose, lipid, and creatinine levels; diabetes; blood pressure; alcohol intake; or smoking.
Conclusions and relevance: The results of this study suggest that bariatric surgery in individuals with obesity is associated with a reduced risk of skin cancer, including melanoma.
Trial registration: ClinicalTrials.gov identifier: NCT01479452.