First intervention trial in the obese population to provide prospective, controlled cancer-incidence data.

The SOS study started in 1987 and involved 2010 obese patients (body-mass index [BMI] ≥34 kg/m2 in men, and ≥38 kg/m2 in women) who underwent bariatric surgery and 2037 contemporaneously matched obese controls, who received conventional treatment. While the main endpoint of SOS was overall mortality, the main outcome of this exploratory report was cancer incidence until Dec 31, 2005.