Breast cancer patients with high levels of insulin in their blood seem to be more likely to die of their disease. Researchers found that insulin may predict whether a woman's breast cancer recurs after therapy and whether she will die.

In a study of 535 breast cancer patients followed for up to 10 years, those with the highest insulin levels were more than eight times more likely to die and were almost four times as likely to have their cancer recur at a distant site.

Although many of the women in the study were obese, and obesity is known to affect both breast cancer prognosis and insulin levels, obesity alone did not completely explain the link between insulin and poorer cancer survival. Although insulin normally helps promote cell growth, researchers hypothesize that in the breast, insulin can spur the growth of both normal and cancerous cells.

Annual meeting of American Society of Clinical Oncology, New Orleans, May 23