Type 1 Diabetes Linked to Increased Risk of Some Types of Cancer

Commentary by Stephanie H. Read, MD and Derek LeRoith MD, PhD

Type 1 diabetes is associated with an increased risk of some cancer types, including cancer of the stomach, liver, pancreas, endometrium, ovary and kidney, but a reduced risk of other cancer types, including prostate and breast cancer, according to a multicenter study of data from five countries published online ahead of print in Diabetologia.
Cancer within the Pancreas
“We found that the risk of some cancers in people with type 1 diabetes is similar to the risk observed in people with type 2 diabetes in earlier studies,” said lead author Stephanie H. Read, MD, Research Assistant at the Usher Institute of Population Health Sciences and Informatics, University of Edinburgh, Scotland. “This suggests that there may be a similar mechanism leading to the increased risk of some cancers in people with type 1 or type 2 diabetes, such as high blood sugar levels or possibly obesity. Our findings also suggest that long-term insulin treatment does not markedly increase cancer risk.”

“Based on our findings, we do not recommend any changes to current clinical practice,” Dr. Read said. “Lifestyle approaches to mitigate cancer risk, including avoiding smoking, maintaining a healthy weight, and increasing physical activity, apply to people with type 1 diabetes as they do the general population. Healthcare providers should encourage their patients to adopt and maintain healthy lifestyles and to partake in cancer screening programs as recommended for the general population.”

Study Included More Than 9,000 Patients
The study analyzed more than 9,000 cancer cases in people with type 1 diabetes using data from five nationwide diabetes registers: Australia (2000-2008), Denmark (1995-2014), Finland (1972-2012), Scotland (1995-2012) and Sweden (1987-2012). The authors compared these data with cancer rates found in the general population in national cancer registries. The median age at cancer diagnosis was 51.1 years.

When considering all cancers in combination, men with type 1 diabetes showed no overall increase in risk, while women with type 1 diabetes showed a 7% increased risk. The neutral overall cancer risk among men with type 1 diabetes was largely due to a 44% decreased incidence of prostate cancer.

Increased Risk for Several Cancer Types Found
For specific cancer types, the study revealed increased risks of cancers of the endometrium, esophagus, kidney, liver, ovary, pancreas, and stomach in people with type 1 diabetes compared with the general population (Table). In addition to prostate cancer,  rates of breast cancer were reduced among people with type 1 diabetes compared with the general population.

When the authors excluded data for sex-specific cancer types (prostate, testis, breast, cervix, endometrium and ovary), excess cancer risk appeared in both men and women with type 1 diabetes (15% for men and 17% for women).
Table. Risk for Cancer in People With Type 1 DiabetesCancer Risk Highest in the First Year Following Diabetes Diagnosis
The risk for overall cancer occurrence was highest in the first year following diagnosis, with a 2.3-fold increased risk in both men and women. Cancer incidence subsequently declined to the level of the general population after approximately 20 years of having type 1 diabetes among men, but after only five years among women (Figure). The authors emphasize that the highly elevated cancer incidence soon after type 1 diabetes diagnosis is plausibly due to the detection of pre-existing cancers shortly after the diabetes diagnosis (when patients are receiving increased medical attention), rather than any association with the type 1 diabetes disease.
Diabetes TimelineFigure. Hazard ratio of all cancers by duration of diabetes in men and women.
Reprinted from Carstensen et al. Diabetologia. 2016 Feb 29. [Epub ahead of print]. http://creativecommons.org/licenses/by/4.0/

“The increased risk of cancer incidence in the first year following diabetes diagnosis is likely to reflect people with type 1 diabetes receiving increased medical attention at this time leading to the detection of pre-existing cancers earlier,” Dr. Read said. “Alternatively, liver and pancreatic cancers are known to cause diabetes and therefore, diabetes may have been diagnosed prior to the detection of cancer in the year following diabetes diagnosis.”

Clinical Implications
“The study from a number of registries (5 countries) demonstrated an increase in cancer risk for some but not all cancers,” commented Derek LeRoith MD, PhD, Interim Chief, Division of Endocrinology, Diabetes and Bone Diseases, Icahn School of Medicine at Mount Sinai in New York City. “Causation is not possible from registry studies and as such one cannot conclude too much from a practice point of view.”

“Since the median age was 51 years, it suggests that a number of factors may be involved in addition to the possibility of insulin use,” Dr. LeRoith said. “To date, date no evidence exists that insulin injections affect cancer growth, and therefore, one should look for other factors such as the evidence showing that patients with type 1 diabetes are commonly more overweight and that factors involved in the metabolic syndrome may be at play. Insulin resistance, hyperlipemia, and cytokines are possible factors, as seen with the increased cancer risk in patients who are obese and/or have type 2 diabetes.”

“Thus, the implications for practice is for health care providers to help patients with type 1 diabetes improve their lifestyles with weight control diets and exercise,” Dr. LeRoith said.

March 21, 2016

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