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Question: Is there any correlation between breast cancer and diabetes?

Answer: Diabetes is one of the most prevalent chronic conditions worldwide, and breast cancer is the most prevalent cancer in women worldwide. These appear to be two completely different diseases, but there is a correlation between the two. In fact, women who have diabetes have a higher risk of developing breast cancer, and women who have been treated for breast cancer have a higher risk of developing diabetes. Post-menopausal diabetic women are 20 per cent more likely to develop breast cancer than those without diabetes.

What is the link between these two diseases? The common underlying factor seems to be insulin resistance stemming from a poor diet, lack of exercise, and obesity. These factors are all familiar as causes of diabetes, but they are also implicated in the development of breast cancer. Cancer cells have a sweet tooth; they need more glucose than healthy cells to facilitate the growth of the tumour. However, these same cancer cells interfere with the cells of the pancreas, causing them to produce less insulin. Less insulin means more glucose is left floating around in the blood stream, leading to higher blood sugar levels in women with breast cancer.

So, insulin resistance seems to be at the centre of a vicious cycle. Insulin resistance results in poor blood sugar control. This promotes tumour growth. The tumour, in turn, suppresses insulin production, which affects blood sugar control, and the cycle continues. Oestrogen suppression as a result of chemotherapy may also promote diabetes. Medications used in chemotherapy to treat nausea and inflammation can also cause increases in blood sugar levels.

Women who have been diagnosed with breast cancer tend to start developing signs of diabetes after about two years. After 10 years post-diagnosis, breast cancer survivors are 20 per cent more likely to have developed diabetes than other women the same age who did not have breast cancer.

Considering these findings, it is important to develop a more robust screening and prevention programme for women with both diabetes and breast cancer. Women with diabetes need to be screened for breast cancer and women with breast cancer need to be screened for diabetes. A good plan might be to have screenings every six to 12 months along with an annual mammogram and breast MRI/ultrasound. Early screening means early detection, which will have a largely positive impact on the treatment outcomes for both diseases.

Diabetes, in itself, reduces life expectancy. Diabetic patients are 50 per cent more likely to die of any cause than persons without diabetes. Diabetic patients who have breast cancer are more likely to have more advanced cancer and die more quickly from the disease. This is why screening and early detection are so important.

When diabetic women are diagnosed with breast cancer, the health-care team has to ensure that they manage both diseases with the same degree of urgency. Oftentimes, the breast cancer treatment takes priority because it is seen as a more direct threat to the patient’s life. However, both diseases are life-threatening and need to be treated with the same level of urgency. Doctors are often concerned that the side effects of chemotherapy may be more severe in diabetics because their bodies are already functioning at sub-optimal levels, hence, they tend to be less aggressive with the cancer treatment. This approach may prove less effective in treating the cancer, though. It is definitely a balancing act managing both these diseases effectively and that is why the health-care team has to work together to achieve optimal management of both diseases.

The best way to keep both diabetes and breast cancer risk low is to adopt a healthy lifestyle. Ensure your diet is a healthy one which is low in added sugars and processed foods but high in fruits and vegetables, exercise regularly, maintain a healthy weight, reduce alcohol intake, and avoid smoking.

There is some good news for diabetic women, though. Metformin, one of the most popular diabetic drugs, is linked with lower incidences of breast cancer. In fact, Metformin may be used to help treat or even prevent the development of breast cancer in women, even if they don’t have diabetes.

So, yes, there is a link between breast cancer and diabetes. Once women have either of these diseases, regular screening is very important. Lifestyle modifications will also have to be made to help with the management of both diseases. Finally, the health-care team has to develop a robust management plan for both diseases, as both of them need to be treated with the same level of urgency.

Novia Jerry Stewart, MSc, RPh, is a pharmacist who specialises in diabetes care. She may be contacted for diabetes care coaching sessions at diabetescarepharmacist@gmail.com.