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Insulin predicts breast cancer survival: study

Helen Branswell
The Canadian Press

īVery exciting observationī: Finding may lead to low-tech ways of fighting the disease

Helen Branswell
The Canadian Press

WASHINGTON - A team of Toronto researchers 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, they suggest in a new study.

The researchers caution their work should only be considered "hypothesis generating" at this point.

But if they are right, it could mean that low-tech ways of lowering blood insulin levels will become vital weapons in the arsenal used to battle breast cancer. Those include weight loss and, particularly, exercise.

"It will never replace chemotherapy or hormone therapy or radiation or surgery, but it might provide an added benefit to all of those treatments," said Pamela Goodwin, lead author of the study.

"This is early stages. Itīs a very exciting observation. Has the potential to have a significant impact on outcome. Has the potential to allow women to participate in their care, which is very important to a lot of women. But itīs not proven yet."

Dr. Goodwin is a breast cancer researcher at Torontoīs Mount Sinai Hospital. She undertook the study with colleagues from several teaching hospitals and the University of Toronto. It is published today in the January issue of the Journal of Clinical Oncology.

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.

Baseline insulin levels differ from individual to individual, although it is not clear why. What is known, however, is that insulin levels can be lowered by exercise.

Several years ago, Dr. 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 would go on to have their cancer spread.

People who develop metastatic cancer, as it is called, run 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.

Dr. 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 a previous cancer or who were diabetics were excluded from the study. The researchers warn their findings might not apply to breast cancer patients who are also diabetics.

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

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 with those in the lowest quartile.

"It can be seen that, in each category, 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," they wrote.

The chairman of breast cancer research at another Toronto hospital was enthusiastic about the findings, saying they will help scientists tease out why the disease is more aggressive in some women than in others.

And Dr. Steven Narod said this line of research may also help identify a target for new drugs to fight breast cancer.

Just as statin drugs are often prescribed to lower high cholesterol levels, drugs aimed at lowering blood insulin levels may some day be prescribed as part of a breast cancer fighting or prevention regime.

"These levels of hormones tend to be modifiable," said Dr. Narod, of Sunnybrook and Womenīs College Health Sciences Centre, who was not involved in Dr. Goodwinīs research.

"Yeah, lifestyle modification is great. But itīs not that easy to lose weight. And as women go on chemotherapy, thereīs a tendency to gain weight."

Dr. Goodwin also knows that many women with breast cancer rail against the feeling of helplessness that can come with seemingly endless rounds of surgery and unpleasant treatment programs over which they have little or no control.

For them, the knowledge that they could improve their survival chances by modifying their diets and increasing their activity level might prove empowering, she said.

Still, Dr. Goodwin does not want to send the message that women with breast cancer must exercise to survive. Itīs too soon to say that based on her research. Besides, she does not want to add to the sense of guilt some women with breast cancer already feel.

"I always have this concern that Iīm going to lead to another decade of women with breast cancer feeling guilty because they havenīt exercised three times a day," she said in an interview.

"And I donīt want that."

Reprinted from:

The Breast Cancer Awareness Month Story  Oct 03 2002
New concerns over breast screening  Sep 25 2002
When Healing Becomes a Crime  Jul 29 2002
Fish Oil Reduces Breast Cancer  Jun 08 2002
Most Women Satisfied With Having Their Healthy Breasts Removed  May 28 2002
Insulin and Estrogen linked to Breast Cancer  May 28 2002
Hormone Replacement Casually Related to Breast Cancer  May 28 2002
Pesticides Increase Breast Cancer Risk  May 28 2002
Healthy Women Having Their Breasts Removed  May 28 2002
Unnecessary Mastectomies  May 28 2002
Do Killer Microbes Cause Breast Cancer?  May 15 2002

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