Long-term incidence of haematological cancer after bariatric surgery or usual care in the Swedish Obese Subjects study: a prospective cohort study.

Background: Bariatric surgery in people with obesity is associated with a reduced overall cancer risk. Retrospective studies indicate that bariatric surgery specifically might reduce the risk of haematological cancers, but there is an absence of data from long-term, prospective studies. We therefore studied the association between bariatric surgery and haematological cancer in the Swedish Obese Subjects study.

Methods: The prospective controlled Swedish Obese Subjects study was designed to compare overall mortality in people who underwent bariatric surgery (n=2007) and usual care (n=2040). Participants were recruited through campaigns in mass media and at 480 primary health-care centres all over Sweden. The inclusion criteria were an age of 37-60 years and a BMI of 34 kg/m or more in men and 38 kg/m or more in women before or at the time of the examination. Haematological cancer events, including malignant lymphoma, myeloma, myeloproliferative neoplasms, as well as acute and chronic leukaemias, were captured from the Swedish Cancer Registry. The main outcome of this study was haematological cancer incidence and mortality. This study is registered with ClinicalTrials.gov (NCT01479452) and is ongoing.

Findings: A total of 4047 individuals with obesity were enrolled between Sept 1, 1987, and Jan 31, 2001. Overall, 34 participants in the surgery group and 51 participants in the usual care control group were diagnosed with haematological cancer during follow-up (hazard ratio [HR] 0·60; 95% CI 0·39-0·92; p=0·020). Moreover, there were three deaths by haematological cancer in the surgery group and 13 deaths in the control group (0·22; 0·06-0·76; p=0·017). Surgery was also associated with a reduced incidence of lymphoma (0·45; 0·23-0·88; p=0·020). A significant difference in treatment effect between men and women was found; bariatric surgery was associated with reduced incidence of haematological cancer in women (0·44; 0·26-0·74; p=0·002), but not in men (1·35; 0·58-3·17; p=0·489; interaction p=0·031).

Interpretation: Bariatric surgery is associated with a reduced incidence of haematological cancer, specifically in women. Health-care providers and policy makers working in the field of cancer prevention should consider bariatric surgery a primary prevention resource for people with obesity.

Funding: The Swedish Research Council, the Swedish State under the agreement between the Swedish Government and the county councils, the Avtal om Läkarutbildning och Forskning agreement, the Health & Medical Care Committee of the Region Västra Götaland, the Swedish Heart Lung Foundation, Gothenburg Medical Society, and the Adlerbert Research Foundation.

Translation: For the Swedish translation of the abstract see Supplementary Material section.