A genetic test to identify women with early-stage breast cancer who are unlikely to benefit from chemotherapy and can effectively be treated with drugs alone has proved successful in a new trial, researchers say.

Such women, treated with hormone-based anti-tumor drugs, can expect a 98 percent survival at five years and a 93.8 percent chance of being free of invasive breast cancer during that time, they say.

The key to identifying which women might fall in that category is a genetic test known as Oncotype DX, which analyzes 21 genes in a breast cancer tumor to asses how aggressive it might or might not be, researchers are reporting in the New England Journal of Medicine.

The researchers tested 10,273 women aged 18 to 75 diagnosed with early-stage hormone receptor-positive breast cancer — cancer driven by estrogen or progesterone — to produce a score predicting the risk of breast cancer recurrence.

The test scores can range from 0 to 100, with higher scores representing a higher risk.

In a trial, women with an Oncotype DX score of less than 11 underwent drug hormone therapy alone without chemotherapy, and after five years, were found to be doing remarkable well, says lead study author Dr. Joseph Sporano at the Montefiore Medical Center in New York.

"What we've shown is that if you have a low recurrence score, you do really, really well with [hormone] therapy alone," he says. "The likelihood of responding to chemotherapy would be nil."

A cancer specialist who not was involved in the study, Dr. Clifford Hudis of New York's Memorial Sloan Kettering Cancer Center, says he agrees with that assessment.

"There is really no chance that chemotherapy could make that number better," he says. Using the Oncotype DX test "lets us focus our chemotherapy more on the higher-risk patients who do benefit" while sparing others the ordeal of chemotherapy, he added.

Mary Lou Smith, an advocate and breast cancer survivor herself, helped to design the study trial. She says she believes women "would be thrilled" at the chance to skip chemotherapy.

"Patients love the idea of a test" to help reduce or remove uncertainty about treatment options, she says. "I've had chemotherapy. It's not pretty."

The Oncotype DX test has been available as a laboratory test since 2004, and its $4,175 cost is covered by Medicare and many insurance companies.