The most common type of breast cancer is early stage, without spread to lymph nodes, and is hormone-positive. The tumor’s growth is being fueled by estrogen or progesterone. Each year, more than 100,000 women in the United States are diagnosed with this.

The usual treatment for this type of cancer is surgery followed by years of a hormone-blocking drugs. Many women also are urged to have chemotherapy. Most of these women do not need chemo, but up until now physicians have been unable to tell which women can avoid it.

Recent studies, however, have shown that a test called Oncotype DX is proving remarkably effective. The test measures the activity of genes that control cell growth to indicate the tumor’s likely response to hormone therapy treatment. Thus, the tumor doesn’t need to be treated with chemo drugs, but instead hormone-blocking drugs.

In the studies, women who skipped chemo based on the test had less than a one 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.”

For more on this story, click CBS News Big change ahead for early breast cancer treatment?

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K.J. McElrath is a former history and social studies teacher who has long maintained a keen interest in legal and social issues.