Bariatric surgery was linked to fewer obesity-related cancers, but more pancreatic cancer

Design

Population-based registry cohort (Nordic Obesity Surgery Cohort)

Population

784,105 adults aged 18 to 59 with obesity; 99,614 had bariatric surgery

Primary outcome

Incidence of obesity-related cancer

Effect

aIRR 0.81 (95% CI 0.77 to 0.85); pancreatic cancer aIRR 2.21 (1.44 to 3.39) in younger adults

This Nordic registry cohort followed 784,105 people aged 18 to 59 with an obesity record in Denmark, Finland or Sweden, of whom 99,614 had bariatric surgery. Surgery was associated with a lower rate of obesity-related cancer overall (adjusted incidence rate ratio 0.81, 95% CI 0.77 to 0.85), with similar estimates in those aged 18 to 39 and 40 to 59 and in men and women.

The strongest associations were for liver cancer (aIRR 0.49, 0.34 to 0.70), endometrial cancer (0.51, 0.45 to 0.59) and ovarian cancer (0.73, 0.60 to 0.87). Pancreatic cancer was the exception: its rate was higher after surgery, particularly in younger adults (aIRR 2.21, 1.44 to 3.39).

This is observational, so selection into surgery may explain part of the pattern. The pancreatic signal is unexplained and based on few events, so it is worth watching but not a reason to withhold surgery.

• Bariatric surgery was associated with about a fifth fewer obesity-related cancers overall.
• Liver and endometrial cancers showed the largest reductions.
• Pancreatic cancer was higher after surgery, especially in adults under 40; the cause is unknown.
• Mention cancer risk as one of several long-term outcomes in counselling, not as a promised benefit.
• Keep standard cancer screening in place after surgery.

Why it matters

It widens the case for bariatric surgery to younger adults while flagging a pancreatic signal to follow.

Don't overread it

The study is observational and the pancreatic cancer result is an unexplained association, not a demonstrated harm.

The statistics, in plain English

An adjusted incidence rate ratio of 0.81 means about 19% fewer cancer diagnoses per person-year after surgery than in comparable people without it, after accounting for measured factors. Unmeasured differences between those who choose surgery and those who do not can still drive the result.

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