Almost seventy percent of women diagnosed with the early stages of one of the most common forms of breast cancer might be able to skip grueling chemotherapy, according to a new study.

The breakthrough research was introduced at the American Society of Clinical Oncology meeting in Chicago over the weekend, and simultaneously published in the New England Journal of Medicine. 

Scientists that patients with smaller-sized tumors that had not spread to the lymph nodes did just as well without chemo as those who got the treatment.  They got tehre by analyzing how well a widely used genetic test assessed cancer risk, based on 21 genes linked with breast cancer recurrence.

"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," wrote lead author Dr. Joseph A. Sparano of the Albert Einstein Cancer Center. 

The new study is called the TAILORx trial.  It followed 9,717 women aged 18 to 75.  Of this group, 67 percent had the early-stage disease with estrogen-receptor-positive, HER2-negative cancers that had not spread to the lymph nodes, scoring in the middle range of the 21-gene test.  In the past, doctors have been unsure whether chemo would be helpful to these sorts of patients.

After surgery and radiation, those women were randomly assigned to receive chemotherapy with an estrogen-blocking medication or just the estrogen hormone blocker.  Nine years later, 84.3 percent in the anti-estrogen plus chemotherapy group were cancer free - but so were 83.3 percent of women treated with just an anti-estrogen medication. 

There are many reasons why women who can avoid chemo would want to avoid it.  Side effects include hair loss, nausea, and vomiting; but chemo can also potentially leave a woman with a depressed immune system, a life-threatening situation.  Long-term, it can leave a woman with permanent numbness and tingling.