A registry study in Denmark found that having cancer was associated with an increased risk of developing type 2 diabetes. Lung cancer, breast cancer and pancreatic cancer are especially associated with increased risk. A researcher says further studies are required to determine the causal relationship.
A new study based on data for more than 1.3 million people in Denmark has concluded that having certain types of cancer considerably increases the risk of developing type 2 diabetes.
The study shows that people with cancer of the breast, lung, urinary tract, uterus or pancreas have between 10% and 500% higher risk of developing type 2 diabetes than people without cancer.
According to a researcher behind the study, the discovery is interesting and should lead to further studies to establish the mechanism for this association.
“I hope that more oncologists will become aware of this association, so that we can determine why people with cancer have an increased risk of developing type 2 diabetes but also why people with both cancer and type 2 diabetes do not survive as long as people with only cancer,” explains Lykke Sylow, Associate Professor, Department of Biomedical Sciences and Department of Nutrition, Exercise and Sports, University of Copenhagen.
The research, published in Diabetes Care, was carried out in collaboration with Christoffer Johansen, Professor, Cancer Survivorship and Treatment Late Effects (CASTLE), Rigshospitalet, Copenhagen; Christen Lykkegaard Andersen, Professor, CopLab Database, Section of General Practice, Department of Public Health, University of Copenhagen; and Steno Diabetes Center Copenhagen.
Examined data for 1.3 million people
The researchers mined the data from the CopLab database, which uniquely contains blood test results and information on the development of type 2 diabetes for more than 1.3 million people.
The researchers linked these data with data from Denmark’s cancer registries to find people with cancer and compare the development of type 2 diabetes between people with and without cancer.
The researchers had data for a 10-year period and included data for about 51,000 people with cancer, comparing them with more than 500,000 people without cancer for a median follow-up time of 2.5 years.
“The purpose of the study was to learn more about some of the comorbidities of cancer. We now know a lot about cancer, and we have also become good at treating and curing many people with cancer. We also know that people with diabetes have an increased risk of developing cancer and that people with cancer and diabetes have an increased risk of death. So far, however, we have not known much about whether cancer increases the risk of developing type 2 diabetes. Studies in mice have indicated this, but we wanted to confirm it among people,” says Lykke Sylow.
Several types of cancer increase the risk of type 2 diabetes
The results show that cancer increases the risk of developing type 2 diabetes by 10% overall.
However, some types of cancer are associated with considerably higher risk: 38% for lung cancer and 20% for breast cancer. Pancreatic cancer has the highest increased risk: 500%.
Cancer of the uterus, brain and urinary tract is also associated with substantially increased risk of developing type 2 diabetes.
“These types of cancer are not necessarily linked to the usual risk factors for developing type 2 diabetes. Further, they are the most common types of cancer that affect many people. This makes the results clinically relevant,” explains Lykke Sylow.
Comorbidity increases the mortality risk
In the second part of the study, the researchers investigated whether having both cancer and type 2 diabetes increases the mortality risk. People with cancer and type 2 diabetes had 21% increased risk of dying within the median follow-up time of 2.5 years.
According to Lykke Sylow, an increased risk of dying from two diseases versus one is not surprising.
“But it provides interesting considerations, including whether people with cancer should be screened for type 2 diabetes and whether screening could help to reduce this increased risk of dying. We lack knowledge about this. Many other people are screened for diabetes, including people with obesity and pregnant women, so perhaps people with some types of cancer should also be screened,” she says.
Further studies needed
Lykke Sylow thinks that this study should lead to more studies of the associations between certain types of cancer and the increased risk of developing type 2 diabetes.
She would like to see studies that can clarify why breast cancer, lung cancer and other types of cancer especially increase the risk of developing type 2 diabetes. The association could result from the type of cancer but could also result from the drug treatment.
“I hope that more oncologists become aware of this association and strive to find the cause, which can help to facilitate more studies,” says Lykke Sylow.
However, she points out some caveats in the study that must be considered before the results are confirmed.
The researchers did not investigate subtypes of cancer and did not investigate which drugs the people with cancer were taking, both of which could be relevant for the results.
“We do not want people with cancer to be concerned about developing type 2 diabetes. The vast majority might not need to worry at all, because only a few with special characteristics have a markedly increased risk and the rest do not at all. We need to determine this,” concludes Lykke Sylow.