Study design and findings
It is well established that obesity is a risk factor for 13 types of cancer, and some of these cancers (liver, pancreatic, endometrial, colon and rectal, breast, and bladder) may be related to type 2 diabetes. And bariatric surgery has been shown to reduce cancer risk in patients with obesity.
However, it is not clear how bariatric surgery may affect cancer risk in patients with obesity and type 2 diabetes.
To study this, the researchers examined data from 393 patients who underwent bariatric surgery and 308 patients who received usual obesity treatment, who were part of the SOS study.
The SOS study enrolled men with a body mass index of at least 34 kg/m2, and women with a BMI of at least 38 kg/m2 who were aged 37-60 years between 1987 and 2001.
The current study outcome – cancer incidence in patients with obesity and type 2 diabetes – was not a prespecified outcome
The intervention groups were matched on 18 variables, including age, sex, serum insulin, alcohol, education, and smoking.
At baseline, the patients had a mean age of about 49 and 60% were women. They had a mean BMI of about 42 and a mean hemoglobin A1c of 7.8%.
On average, patients in the surgery group had lost 27.5 kg and 22.7 kg, and patients in the usual care group had lost 3.2 kg and 4.8 kg, at 2 years and 10 years, respectively.
During a median follow-up of 21 years, there were 74 incident cancers in the control group and 68 cancers in the bariatric surgery group.
The risk of cancer during follow-up was 37% lower in the surgery group than in the usual care group, after multivariable adjustment (adjusted hazard ratio, 0.63; 95% confidence interval, 0.44-0.89; P = .008).
A deeper dive showed that there were 86 incident cancers in women and 56 cancers in men. The risk of cancer was significantly lower in women who had bariatric surgery, compared with those who had usual care (aHR, 0.58; 95% CI 0.38-0.90, P = .016). However, the risk of cancer was not significantly lower in men who had bariatric surgery versus those who had usual care (aHR 0.79, 95% CI, 0.46-1.38; P = .413).
Diabetes remission at 10 years was associated with a 60% reduced cancer incidence (aHR, 0.40; 95% CI, 0.22-0.74, P = .003).
The study was funded by the Swedish state (under an agreement between the Swedish government and the county councils), the Swedish Research Council, the Novo Nordisk Foundation, the Swedish Heart-Lung Foundation, and the Swedish Diabetes Foundation. One author received consulting fees from Johnson & Johnson. The other authors had no relevant financial disclosures.
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