People with obesity who had bariatric surgery were about 20% less likely to develop cancers linked to excess weight than people with obesity who did not have the operation, according to a registry study covering Sweden, Denmark and Finland.
The size of the study
Researchers followed more than 780,000 people with obesity, of whom nearly 100,000 had undergone surgery. The work, led from the Karolinska Institute and published online in JAMA Surgery, looked at ten cancers associated with obesity, including cancers of the breast, endometrium, colon, kidney, liver and pancreas.
Registry studies of this kind cannot prove cause and effect. People who qualify for surgery and complete it tend to differ from those who do not in ways that records do not capture, including motivation, other illnesses and access to care. The authors adjusted for age, sex, calendar period, education and several metabolic conditions.
Consistent across groups
The reduction held across age bands and was similar for men and women when the analysis was restricted to cancers that occur in both sexes. That matters because earlier work was dominated by breast and endometrial cancer, both of which are strongly tied to obesity and to female sex hormones.
The team also looked at how the effect changed with time since surgery. The gap widened with longer follow-up, which fits the idea that sustained weight loss, rather than the operation itself, drives the difference.
What doctors say it means
Lead author Cecilia Radkiewicz, a medical oncologist at Karolinska, said the main reason to operate remains weight loss, not cancer prevention. But she argued that because the benefit looks similar for men and women and across age groups, access to surgery should be equitable whenever it is clinically indicated.
That is a policy point as much as a clinical one. Waiting lists for bariatric surgery are long in all three countries, and health systems ration slots by body mass index, diabetes status and age. If the cancer benefit is broad, rationing rules that favour younger women with diabetes may need a second look.
Patients should not read the result as a substitute for screening. The study found lower risk, not zero risk, and the cancers involved are still detected mostly through existing programmes.