Cancer Risks with Type 1 Diabetes

People with type 1 diabetes (T1DM) suffer from increased cancer rates, which are slightly lower than the increased risk found in people with type 2 diabetes (T2DM), according to a study published online in Diabetologia. The study also found increased risk for certain types of cancer, and decreased risk of prostate and breast cancer among people with T1DM.

The study was conducted by the Diabetes and Cancer Research Consortium, and is the largest to date to evaluate the links between cancer and T1DM.

“We found that, on average, type 1 diabetes confers an excess incidence of several cancers.  In particular, persons with type 1 diabetes had a higher incidence of cancer of the liver, pancreas, kidney, endometrium and ovary and a lower incidence of prostate cancer than those in the general population,” wrote first author Bendix Carstensen, MSc, of the Steno Diabetes Centre in Gentofte, Denmark, and colleagues.

Diabetes has been associated with 20-25% increased incidence of cancer. In particular, diabetes has been linked to increased incidence of liver, pancreatic, colorectal, endometrial, and kidney cancers, and decreased incidence of prostate cancer, according to background information in the article.

Study cohorts, though, have been comprised mostly of people with T2DM, leaving the links between cancer and T1DM relatively unknown.

In the study, researchers used nationwide registries to identify people with T1DM in the following countries and during the following years (in parentheses): Australia (2000-2008), Denmark (1995-2014), Finland (1972-2012), Scotland (1995-2012), and Sweden (1987-2012). Then they used national cancer registries to identify incident cancers in people with T1DM.

The study identified 9149 cancers overall, with a median age at diagnosis of 51.1 years

Key results (compared to the general population):

• Overall non-sex specific cancers: 17% higher in women (HR 1.17 [95% CI 1.13-1.22]), 15% higher in men (HR 1.15 [95% CI 1.11-1.19])

• Significantly increased risk of:

♦ Stomach cancer: 78% higher in women (HR 1.78, [95% CI 1.48-2.13]); 23% higher in men (HR 1.23, [95% CI 1.04-1.46])

♦ Liver cancer: 55% higher in women (HR 1.55, [95% CI 1.14, 2.10]), two times higher in men (HR 2.00, [95% CI 1.67-2.40])

♦ Pancreatic cancer: 25% higher in women (HR 1.25, [95% CI 1.02-1.53]), 53% higher in men (HR 1.534, [95% CI 1.30-1.79])

♦ Endometrial cancer: 42% higher in women (HR 1.42, [95% CI 1.27-1.58])

♦ Ovarian cancer: 15% higher (HR 1.15 [95% CI 1.02-1.30])

♦ Kidney cancer: 47% higher in women (HR 1.47, [95% CI 1.23, 1.77]), 30% higher in men (HR 1.30, [95% CI 1.12, 1.49])

• Significantly decreased risk of:

♦ Prostate cancer: 44% lower (HR 0.56, [95% CI 0.51-0.61])

♦ Breast cancer: 10% lower (HR 0.90, [95% CI 0.85-0.94])

• The risk of cancer decreased with increasing duration of diabetes

♦ The highest risk occurred in the first year after diagnosis (men, HR 2.28 95% CI 1.87-2.78, women HR 2.34, 95% CI 2.00, 2.74)

The authors provided several explanations for these results.

The increased rates of cancer during the first year after diagnosis may have been due to earlier diagnosis of pre-existing cancers, they wrote, and less likely due to types of cancer that cause diabetes (like pancreatic cancer).

Past studies, mostly in T2DM, have suggested similar or increased risk of breast cancer compared to the general population. The decreased breast cancer risk found in this study may reflect younger age of the cohort (less postmenopausal women), or may have been confounded by other breast cancer risk factors, according to the authors.

Lower incidence of prostate cancer has also been found in T2DM, they mentioned, suggesting a similar mechanism for T1DM and T2DM, such as lower testosterone levels in men with diabetes.

Some studies have suggested that insulin may increase the risk of cancer. However, findings from this study do not support this idea. The risk of overall cancers in this study was lower in T1DM compared to estimates for T2DM from other studies. Because all patients with T1DM are treated with insulin and only a fraction of those with T2DM receive insulin, the link between T1DM and cancer would be expected to be stronger if insulin were involved.

The risk of specific cancers in T1DM, however, were similar to the risks in T2DM, suggesting common mechanisms for these cancers. The highest risk occurred in cancers for which obesity is an established risk factor: stomach, kidney, endometrial, and pancreatic cancers. Obesity is increasingly common in T1DM, the authors noted, which may add to the risk of these types of cancers.

 “Our findings do not support changing the policy for cancer screening in persons with type 1 diabetes,” they concluded, “Similar recommendations for lifestyle approaches to reduce cancer risk such as weight management, increasing physical activity and avoiding smoking apply to persons with type 1 diabetes as for the general population.”

Take-home Points

• A five-country study has linked T1DM to increased risk of cancer.

• T1DM was significantly linked to increased risk for stomach, liver, pancreatic, endometrial, ovarian, and kidney cancer.

• T1DM was significantly linked to decreased risk of breast and prostate cancer.

• Incidence of cancer was highest in the first year after diagnosis, and declined over time.

Dr. Carstensen is an employee of the Steno Diabetes Center, owned by Novo Nordisk. Sarah Wild reports honoraria from Global MedEd/Astrazeneca.

Reference: Carstensen B, et al. Cancer incidence in persons with type 1 diabetes: a five-country study of 9,000 cancers in type 1 diabetic individuals. Diabetologia. 2016 Feb 29.