High insulin levels linked to deaths from breast cancer

High fasting concentrations of insulin may be an independent risk factor for poor outcomes in women with breast cancer, according to a study presented at the annual meeting of the American Society of Clinical Oncology, in New Orleans, Louisiana. The study shedssome light on cell growth and may lead to new therapeutic avenues.

Researchers from the University of Toronto Mount Sinai Hospital led by Dr Pamela Goodwin followed 535 women with breast cancer for 10 years and studied the relation between breast cancer grade and stage and insulin concentration. Fasting insulin concentrations were measured to avoid postprandial fluctuations.

Cancer grade refers to the nuclear and histological appearance of the tumour cells (low, high, or intermediate grade corresponding to how differentiated the tumour seems), and stage refers to the level of spread of the tumour. Generally, higher grade cancers tend to be more aggressive and progress to higher stages.

Patients enrolled in the study received standard accepted treatments of surgery with chemotherapy, hormonal therapy, and radiotherapy if indicated. The researchers found that women with the highest insulin levels were eight times more likely to die during the study than women with the lowest insulin levels, with 70% of such patients being alive after seven years compared with 95% of those with normal insulin levels.

Moreover, those with high insulin levels were four times more likely to suffer metastatic disease and disease recurrence. Although many of the women in the study were obese, and obesity is itself associated both with a greater risk of breast cancer and with insulin resistance, in this study insulin level alone was found to be an independent risk factor for breast cancer. Dr Goodwin said that some women of normal weight in the study also had high insulin levels and that the worse prognosis held for them as well.

It is not entirely surprising to find that insulin may be implicated in breast cancer. While insulin is usually thought of in association with diabetes and as the key to controlling blood sugar levels, it is also a cellular growth factor. Previous studies have shown that the cell surface receptor for insulin on breast cancer cells differs from that of normal cells. High insulin levels, alone or in concert with defective insulin receptors, may promote neoplasia.

Although further research is needed to confirm and clarify the role of insulin in breast cancer, the finding suggests that patients with breast cancer and high insulin levels may be able to reduce risk of progression by modifying their diet and exercising to decrease insulin levels.