Breast Cancer and Type 2 Diabetes


Type 2 diabetes impacts over 400 million people worldwide and accounts for 90-95 percent of all diagnosed diabetes cases. In the United States, 15 million—1 in 9 women—have diabetes. While not type-specific, the International Diabetes Federation estimated 199 million women live with diabetes and that number is expected to increase to 313 million by the year 2040. Globally, diabetes is the ninth leading cause of death in women and it can be attributed to over two million deaths per year. If you factor in breast cancer, a disease that specifically affects women, the outcomes are worse. Diabetes affects up to one-third of patients with breast cancer. But how are breast cancer and type 2 diabetes-related?

The Relationship Between Breast Cancer and Type 2 Diabetes

Currently, the relationship between breast cancer and type 2 diabetes is unclear, however, there are studies that show the overlapping risk factors between the two diseases. Examples of these risk factors include:

  • Overweight or obesity
  • Lack of physical activity
  • Age
  • Post-menopause
  • Prior treatments such as chemotherapy
  • Diabetes duration
  • Preexisting cardiovascular disease
  • Health care access disparities

Studies show having type 2 diabetes may increase the risk of breast cancer by about 20-27 percent. Compared to women without diabetes, a study in Diabetes Care showed the risk of developing a more aggressive form of breast cancer is higher among women with type 2 diabetes. Post-menopausal women who have diabetes also have a higher risk of breast cancer than women without diabetes.

Diabetes can have an impact on breast cancer treatments, as well. Women with diabetes and its complications, especially cardiovascular disease, receive less aggressive cancer treatments, particularly with chemotherapy. The risk for cardiovascular disease is higher in women with diabetes, which could impact a doctor’s decision making in choosing a cancer treatment regimen and opt for a conservative approach to chemotherapy.

Diabetes Medications That Impact Breast Cancer Risk

In type 2 diabetes, patients are treated with oral and injectable medications, and depending on the progression of diabetes, insulin. Some diabetes medications have been evaluated for their impact on cancer. According to a review by oncologists, evidence shows metformin and TZDs are associated with a decreased risk in the incidence of cancer. For other diabetes medications such as SGLT2s, GLP-1 RAs, insulin and sulfonylureas, their effects on cancer remain unclear.

Are Certain Groups of Women More Likely to be Affected than Others?

In short, yes, but the incidence and mortality rates of breast cancer among women with diabetes vary and the link between ethnicity, diabetes and breast cancer is still being studied. An observational study showed type 2 diabetes increased the risk of an aggressive form of breast cancer in African-American/Black women, who had diabetes for at least five years, by more than 40 percent. White women have a 20 percent increased risk of developing breast cancer, however, Black/African-American women have a 40 percent higher mortality rate. Another study focused on the links between obesity/body mass index (BMI), type 2 diabetes and breast cancer. The results showed though the inclusion of BMI weakened the link between type 2 diabetes and breast cancer, Latina women with type 2 diabetes were more likely to have breast cancer than other ethnic groups. In Asian women, there’s also an increased risk of breast cancer with diabetes, however, more research is needed to assess this group as well.

How Can I Lower My Risks of Breast Cancer if I Have Type 2 Diabetes?

So what should you do to lower your risks of breast cancer? Fortunately, a lot of the same things that go into diabetes management can decrease your chances.

  • Manage blood sugar. Keep your blood sugar in range and aim to improve insulin sensitivity.
  • Eat a healthy diet. Maintain a balanced diet of unprocessed foods, fruits and vegetables, healthy sources of protein and foods low in sugar.
  • Avoid smoking. Smoking is a risk for various kinds of cancer. Young and premenopausal women who smoke are at a higher risk for breast cancer.
  • Exercise. Physical activity can lower the risk of breast cancer and improve your immune system.
  • Self-breast exam. Conduct a self-breast exam once a month. Follow the steps here on how to do it. Alert your doctor if you detect a lump or notice any other changes. Early detection is important.
  • Get screened. If you haven’t done a self-exam or noticed you haven’t been screened lately, ask your physician to perform a breast exam.

WRITTEN BY T'ara Smith, MS, Nutrition Education, POSTED 11/20/20, UPDATED 06/10/22

T’ara was diagnosed with type 2 diabetes in July 2017 at the age of 25. Since her diagnosis, she focused her academic studies and career on diabetes awareness and living a full life with it. She’s excited to have joined the Beyond Type 1 team to continue her work. Two years later, T'ara discovered she'd been misdiagnosed with type 2 and actually has latent autoimmune diabetes in adults (LADA). Outside the office, T’ara enjoys going to the movies, visiting parks with her dog, listening to BTS and cooking awesome healthy meals. T’ara holds an MS in Nutrition Education from American University.