Many women with early-stage breast cancer can skip chemotherapy without hurting their odds of beating the disease – good news from a major study that shows the value of a gene-activity test to gauge each patient’s risk.

The test accurately identified a group of women whose cancers are so likely to respond to hormone-blocking drugs that adding chemo would do little if any good while exposing them to side effects and other health risks. In the study, women who skipped chemo based on the test had less than a 1 percent chance of cancer recurring far away, such as the liver or lungs, within the next five years.

“You can’t do better than that,” said the study leader, Dr. Joseph Sparano of Montefiore Medical Center in New York.

An independent expert, Dr. Clifford Hudis of New York’s Memorial Sloan Kettering Cancer Center, agreed.

“There is really no chance that chemotherapy could make that number better,” he said. Using the gene test “lets us focus our chemotherapy more on the higher risk patients who do benefit” and spare others the ordeal.

The study was sponsored by the National Cancer Institute. Results were published online Monday by the New England Journal of Medicine and discussed at the European Cancer Congress in Vienna.

The study involved the most common type of breast cancer – early stage, without spread to lymph nodes; hormone-positive, meaning the tumor’s growth is fueled by estrogen or progesterone; and not the type that the drug Herceptin targets. Each year, more than 100,000 women in the United States alone are diagnosed with this.

The usual treatment is surgery followed by years of a hormone-blocking drug. But many women also are urged to have chemo, to help kill any stray cancer cells that may have spread beyond the breast and could seed a new cancer later.