The study showed an increase in cancer incidence in type II diabetes

People with type II diabetes are more likely to develop new cancers than people without the disease. In recent decades, the difference between the groups has grown, especially for tumors that are associated with obesity at the population level. About what the study of the Danish medical registers showed and why its results do not prove that diabetes causes cancer, in the "Izvestia" article.

How the study was conducted

The researchers studied data from Denmark's national medical registers for 1996-2022. The analysis included information about the adult population of the country — people over the age of 18 with and without type II diabetes. The researchers were interested in the first cases of cancer and how their frequency differed in the two groups over the course of 27 years.

Before the diagnosis of "type II diabetes", a person was classified as a group without diabetes, after that — as a group with the disease. Monitoring of each participant was completed upon detection of cancer, death, departure from the country, or at the end of 2022. During the entire period, researchers registered 75,540 first cancer cases among people with type II diabetes and 635,323 among people without it. These absolute numbers cannot be directly compared as an indicator of personal risk: the frequency of new cases in each group is important.

The results were published by the European Association for the Study of Diabetes (EASD). The study is scheduled to be presented at its annual conference in Milan, which will be held from September 28 to October 2, 2026. On September 24, we are talking about a message for an upcoming report, and not about a speech that has already taken place.

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How much difference has grown

In 2010-2022, the overall incidence of cancer among men with type II diabetes was 12% higher than among men without diabetes. Among women, the difference was 22%. For comparison, in 1996-2009, these figures were 9% and 15%, respectively. Thus, the researchers observed an increase in the relative difference between the groups, and in women it was more noticeable.

The difference was especially pronounced for the group of cancers associated with obesity. In 2010-2022, their incidence among men with diabetes was 45% higher than among men without diabetes, and 30% higher among women. In the earlier period, the differences were 34% and 23%, respectively. At the same time, the designation "associated with obesity" refers to a known association at the population level.: This does not mean that obesity explains every case of the disease or all the differences found in this study.

For which types of cancer were the differences found?

The picture depended on the sex and type of tumor. In 2010-2022, the incidence of colorectal cancer — colon and rectal cancer — among men with type II diabetes was 17% higher than among men without diabetes. For women, the difference was 14%. Breast cancer after menopause was detected among women with diabetes by 8% more often.

Differences were also observed for lung cancer, which was not classified in the study as a group of tumors associated with obesity. In 2010-2022, its incidence among men with diabetes was 23% higher, and among women it was 25% higher than among people without diabetes of the corresponding gender. In women, the indicator has changed especially noticeably compared to 1996-2009: then, on the contrary, the incidence of lung cancer in the group with diabetes was 12% lower. The current analysis does not establish the reasons for this change.

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The increased incidence did not apply to all types of cancer. For example, prostate cancer in 2010-2022 was detected 19% less frequently among men with type II diabetes than among men without it. Therefore, the overall indicator for all tumors does not describe the risk of each individual disease.

Does this mean that diabetes causes cancer?

The authors emphasize that the study describes differences in morbidity, but does not establish their cause. People with and without diabetes may have different body weight, smoking prevalence, alcohol consumption, and physical activity levels. It was not part of the task of the work to determine the contribution of these factors to the detected difference.

Scientists are also considering possible biological explanations for the connection. These include long—term exposure to elevated glucose and insulin levels, insulin resistance, and chronic inflammation. However, the data from the registers themselves do not show which mechanism was at work in specific patients.

The researchers' practical conclusion concerns primarily the monitoring of people with type II diabetes. According to Laurberg, the prevention of cardiovascular diseases and kidney damage remains an important part of helping such patients, but attention should also be paid to early detection of cancer. It is especially important that people with diabetes do not skip existing colorectal cancer and breast cancer screening programs where they are provided.