Bariatric surgery linked to fewer obesity-related cancers at every age — but more pancreatic cancer

Design

Population-based registry cohort (Nordic Obesity Surgery Cohort)

Population

784,105 adults aged 18–59 with obesity in Denmark, Finland and Sweden; 99,614 had surgery

Primary outcome

Incidence of obesity-related cancers

Effect

Adjusted IRR 0.81 (95% CI 0.77 to 0.85); pancreatic cancer aIRR 2.21 in younger adults

A population-based cohort from Denmark, Finland and Sweden followed 784,105 adults aged 18 to 59 with recorded obesity, of whom 99,614 had bariatric surgery.

Surgery was associated with fewer obesity-related cancers overall (adjusted IRR 0.81, 95% CI 0.77 to 0.85), with the same association in under-40s and over-40s and in men and women. The strongest associations were for liver (0.49), endometrial (0.51) and ovarian cancer (0.73). Pancreatic cancer was more frequent after surgery, especially in younger adults (aIRR 2.21, 1.44 to 3.39).

This is observational: people who choose and qualify for surgery differ from those who do not, despite adjustment. The pancreatic signal is unexplained and may reflect surveillance or chance, but it is worth knowing when counselling.

• Include a possible reduction in obesity-related cancer, observed in registry data, when counselling about bariatric surgery.
• Explain that the association held for younger and older adults, and for men and women alike.
• Keep a low threshold for investigating new upper abdominal symptoms after bariatric surgery, given the pancreatic signal.
• Do not present cancer prevention as a proven benefit; it rests on observational data.

Why it matters

The finding that younger patients show the same association supports offering surgery without waiting for age-related comorbidity.

Don't overread it

This is a registry cohort; it shows association, not that surgery prevents cancer, and the pancreatic signal is unexplained.

The statistics, in plain English

An incidence rate ratio of 0.81 means obesity-related cancers were diagnosed about 19% less often after surgery. A ratio of 2.21 for pancreatic cancer means it was about twice as frequent, but pancreatic cancer is rare in young adults, so the absolute number of extra cases is small.

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