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A team of Toronto researchers headed by Goodwin, a breast cancer researcher at Toronto's Mount Sinai Hospital, may have found an easy way to determine which women with breast cancer will respond well to treatment and which are at high risk of dying. Blood insulin levels appear to be a reliable predictor of whether a woman with breast cancer will survive over the long term.

Several years ago, Goodwin and some colleagues published research showing a link between blood insulin levels and the risk of developing breast cancer. This time, they took the work further, looking at whether insulin levels could tell researchers which breast cancer patients would respond well to treatment and which patients would go on to have their cancer spread.

Insulin is a hormone the body needs to regulate sugar levels in the blood. But it also acts as a growth hormone and is known to play a role in the development of some cancers.

Goodwin and her colleagues enrolled 512 women with early breast cancer in their study, using blood samples drawn after an overnight fast to determine their baseline insulin levels.

Women who had had a previous cancer or who were diabetics were excluded from the study. (The researchers warn their findings may not apply to breast cancer patients who are also diabetics).

Dividing the women into four groups, they found that women with insulin levels in the top quartile had a two-fold increased risk of developing metastatic cancer and a three-fold increased risk of death compared to those in the lowest quartile.

They followed the women for a period ranging from three years to over nine years, during which time 76 women developed metastatic disease and 45 died.

People who developed metastatic cancer, as it is called, runs a significantly higher risk of dying. The idea seemed logical. Researchers have already reported that obese women are at increased risk of developing breast cancer and if they do, may not respond as well to treatment as women of healthier weights.

Researchers concluded that higher levels of insulin were associated with poorer outcomes, consistent with the existence of a prognostic effect of insulin across broad categories of body weight.

Baseline insulin levels differ from individual to individual, though why that is isn't clear. What is known, however, is that insulin levels can be lowered by exercise.

Goodwin undertook this study with colleagues from several teaching hospitals and the University of Toronto. The test findings were published in the January 2002 issue of the Journal of Clinical Oncology.