Researchers know that there is an association between obesity and diabetes, and there is an association between diabetes and various forms of cancer, but there have been few long-term studies to track obese patients with diabetes to determine their cancer rates post-surgery. A recent study from Sweden followed patients over a 20 year period to see whether there was a difference in cancer rates between patients with obesity and diabetes who had undergone bariatric surgery and those who did not.
According to the research, the "pattern of increasing obesity and diabetes has led to an increased in cancer prevalence". Some of the cancer rates seem to correlate with diabetes, whereas some of the cancer rates seem to correlate more strongly with obesity. Researchers do not know for sure which cancers are more likely to be associated primarily with diabetes, since there is a strong occurrence of patients with obesity also having diabetes.
The research showed that after two years, almost 70% patients who had undergone surgery were in remission for their diabetes, versus 16% remission for the control group. After 10 years, 35% of surgery patients were still in remission for their diabetes, versus 6.5% in the control group. Surgery patients also lost and maintained a weight loss on average of 50 pounds after ten years, where as the control group had lost and maintained a weight loss of around 10 pounds.
For cancer rates, researchers found "a 37% reduced risk of incident cancer after bariatric surgery in patients with obesity and diabetes". There was more of a reduction in cancer rates in women than with men, which researchers theorize may have to do with the hormones related to certain types of cancer found in women and the insulin response that affects those hormones.
There is still a lot of research that needs to be done in this field. Some of the associations still have unclear causes. For example, obesity is associated with diabetes, but it is still unclear how much of the risk of certain cancers are due more to obesity or to diabetes. In addition, diabetes does increase the risk of certain cancers, but also, cancer survivors have a higher risk of developing diabetes. So many of our health risks are very much intertwined with each other, where it's not as simple as one thing causes another, but various diseases and health concerns impact each other. However, this study does show that for people with obesity and diabetes who choose to undergo bariatric surgery, their risks of developing cancer does decrease and stays at a lower rate for years or decades.
Kajsa Sjöholm, Lena M.S. Carlsson, Per-Arne Svensson, Johanna C. Andersson-Assarsson, Felipe Kristensson, Peter Jacobson, Markku Peltonen, Magdalena Taube; Association of Bariatric Surgery With Cancer Incidence in Patients With Obesity and Diabetes: Long-term Results From the Swedish Obese Subjects Study. Diabetes Care 1 February 2022; 45 (2): 444–450. https://doi.org/10.2337/dc21-1335