Diabetes and Breast Cancer: What Is the Relationship?

Type 2 diabetes increases the risk of breast cancer, but the reason why is not fully understood. It's thought that a few diabetic factors are at play, including:

• High blood sugar
• High insulin levels
• Hormonal imbalances
• Inflammation

This article discusses the connection between diabetes and breast cancer, including the risks of developing breast cancer with diabetes and considerations for how the two conditions can be managed and treated together.

Connection Between Diabetes + Breast Cancer

Diabetes is often talked about with diabetes complications like kidney disease and heart disease, so how is it related to breast cancer? While more research is needed to determine a truly causal link between diabetes and breast cancer, studies have shown some diabetes-related factors are at play:

• High blood sugar (hyperglycemia): This is a risk factor for cancer progression, meaning high blood sugar may lead to tumor cell growth. For example, high glucose levels in people with breast cancer have been shown to increase insulin-like growth factor (IGFBP2) levels, which can lead to resistance to chemotherapy. This can lead to cancer cell growth. Hyperglycemia is also related to hypoxia (low oxygen in tissues), which is known to be a factor in tumor malignancy.
• High insulin levels due to insulin resistance (hyperinsulinemia): This is associated with breast carcinogenesis (the beginning of cancer formation) and cancer cell growth. High insulin levels also induce molecular factors (IGF-1 and HIF-1), which can increase cell growth and estrogen levels.
• Hormonal imbalances: Besides estrogen, other hormones play a role in the connection between diabetes to breast cancer. Research has shown that people with obesity-associated diabetes and high levels of leptin, a hormone made by fat cells, had increased aromatase and estrogen, pro-inflammatory cytokines, and cell growth, all of which can lead to tumor cell growth.
• Chronic inflammation: Diabetes-related inflammation, due to increased levels of inflammatory cytokines and adipokines, may lead to breast tumor growth. It also may induce certain inflammatory response cells that lead to tumor production.

Risks

Research suggests that the risk of breast cancer and diabetes is specific to type 2 diabetes and post-menopause. This means post-menopausal people with type 2 diabetes are at higher risk of developing breast cancer. 

When looking at breast cancer prognosis, research has shown that poorer breast cancer prognosis among those with diabetes is due to diabetes-related comorbidities, not diabetes itself. For example, people with obesity, diabetes, and breast cancer may have a worse breast cancer prognosis due to the effects that obesity has on estrogen levels.

Some research has suggested the main reason behind the increased risk of diabetes and breast cancer is body mass index (BMI); however, BMI is associated with both diabetes and breast cancer, which means it can’t be singled out as the main cause of breast cancer among people with diabetes. 

The risk of death from breast cancer and diabetes is affected by various factors, though how significant some factors are in increasing the risk of death is still unclear. For example, one study showed that people with diabetes and breast cancer are at higher risk of death from breast cancer if they’ve had diabetes for a long time and have cardiovascular disease.

Treatment and Management of Diabetes With Breast Cancer

Breast cancer treatment and type 2 diabetes treatment take very different approaches. While there are some important medical considerations when treating both conditions, they can be managed at the same time.

People with breast cancer and diabetes can still receive appropriate chemotherapy and radiotherapy like individuals with cancer without diabetes. However, some cancer treatments may have negative effects on diabetes management, which calls for special treatment plans by a healthcare provider

For example, some cancer immunotherapies can prevent insulin production or induce insulin resistance, both of which can cause hyperglycemia. 

In addition, underlying diabetes-related conditions may impact which cancer treatments can be used. Some conditions may limit the kinds of drugs used to treat breast cancer and how many of those drugs can be taken. These conditions include:

• Neuropathy
• Heart disease
• Kidney disease

For example, radiation increases the risk of cardiovascular complications, which may make it a complex treatment for people with diabetes, heart disease, and breast cancer.

On the other hand, some type 2 diabetes treatments may have some favorable effects on breast cancer outcomes. For example, metformin—a common medication to control blood sugar—has been found to improve outcomes among people with type 2 diabetes with breast cancer.

Managing diabetes through a healthy diet and physical activity can also have positive impacts on cancer prevention.

Prevention

Type 2 diabetes and breast cancer share some preventive factors, such as maintaining a healthy weight and being physically active. Some risk factors of breast cancer can’t be changed, such as family history, but others can be. 

Since diabetes-related factors can increase the risk of developing breast cancer, diabetes management is important for preventing breast cancer. Here are three factors that are important for both diabetes management and cancer prevention:

• Eat a diet rich in vegetables, fruit, and whole grains, and limit red and processed meat.
• Exercise to maintain a healthy weight and to keep your cardiovascular system healthy
• Do not drink alcohol or drink it only in moderation.

While these lifestyle factors are important for prevention, your health history is unique, and prevention isn’t a one-size fits all approach. It’s best to speak with a healthcare provider if you’re concerned about your risk of breast cancer or diabetes. 

Summary

Type 2 diabetes increases the risk of breast cancer among post-menopausal individuals. High blood sugar, high insulin levels, hormonal imbalances, and chronic inflammation are all factors that can increase the risk.

Management of both breast cancer and diabetes requires a thoughtful treatment plan, as some cancer treatments may affect diabetes-related complications.

Lifestyle changes like more exercise, a healthier diet, and limited alcohol intake can help reduce the risk of developing breast cancer with diabetes.

A Word From Verywell

A breast cancer diagnosis can be hard enough to process and deal with without also having to manage life with diabetes.

If you are post-menopausal with diabetes, knowing there may be an increased risk of breast cancer can be scary. While some things are out of your control—such as having a family history of breast cancer or being more at risk because of your race—some risk factors can be changed. Know that you are not alone in this.

There are many others in your shoes who are also trying to figure out how to live with diabetes and breast cancer or prevent it from happening in the first place. We hope this article provides information that empowers you to take control of what you can change and feel more informed when talking with your doctor about managing these conditions.