Story highlights 70% of women with common form of breast cancer might need only hormone therapy

Genetic test can assess breast cancer to personalize treatment

(CNN) About 70% of women diagnosed with the early stages of one of the most common forms of breast cancer might not need chemotherapy as part of treatment, according to the results of a long-awaited study presented at the American Society of Clinical Oncology meeting in Chicago Sunday.

The study, published Sunday in the New England Journal of Medicine , analyzed how well a widely used genetic test assessed cancer risk, based on 21 genes linked with breast cancer recurrence.

Photos: 7 ways to reduce your breast cancer risk Photos: 7 ways to reduce your breast cancer risk Staying physically active has been associated with a reduced risk of several forms of cancer. Experts recommend exercising at least 150 minutes (2½ hours) per week. Hide Caption 1 of 7 Photos: 7 ways to reduce your breast cancer risk The more alcohol you consume, the greater your risk of developing breast cancer, research suggests. The Centers for Disease Control and Prevention recommends limiting alcoholic drinks to one per day. Hide Caption 2 of 7 Photos: 7 ways to reduce your breast cancer risk Controlling your weight and eating a Mediterranean-style diet has been associated with a reduced risk of breast cancer. Being overweight or obese increases the risk of breast cancer. Hide Caption 3 of 7 Photos: 7 ways to reduce your breast cancer risk Avoid smoking. Accumulating research shows a link between smoking and increased breast cancer risk, especially in premenopausal women. Hide Caption 4 of 7 Photos: 7 ways to reduce your breast cancer risk If you are taking or have been told to take hormone replacement therapy, experts recommend talking to your doctor about associated breast cancer risks. Some studies suggest that using combination hormone therapy for more than three to five years increases the risk of breast cancer. Hide Caption 5 of 7 Photos: 7 ways to reduce your breast cancer risk Breastfeeding children has been associated with a reduced risk of breast cancer. Hide Caption 6 of 7 Photos: 7 ways to reduce your breast cancer risk Undergoing a breast cancer screening, during which your breasts are checked before any signs or symptoms emerge, cannot prevent cancer -- but it can find the disease early. Experts advise talking to your doctor about which breast cancer screening tests and guidelines are right for you. Hide Caption 7 of 7

"These data confirm that using a 21-gene expression test to assess the risk of cancer recurrence can spare women unnecessary treatment if the test indicates that chemotherapy is not likely to provide benefit," lead author Dr. Joseph A. Sparano, associate director for clinical research at the Albert Einstein Cancer Center, said in a statement. The study was sponsored by the National Cancer Institute and led by the ECOG-ACRIN Cancer Research Group.

"I'm delighted," said Dr. Otis Brawley, chief medical and scientific officer for the American Cancer Society, who was not part of the study. "I've been worried for a long time about unnecessary treatment for cancer, and unnecessary side effects from chemotherapy.

"Now with these genomic tests, we are finding that we have multiple types of breast cancer, perhaps several dozen," said Brawley, "and we are being able to tailor our therapies to the type of breast cancer every woman has."

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