After a  mammogram, Dorothy Warren learned she had something called DCIS -- almost breast cancer, but not quite the same.

"You're gonna tell me I have cancer and I have stage zero, and it's not real invasive cancer?  I was not only fearful, but confused," Warren said.

Dr. Pamela Otto, a breast radiologist at the University of Texas, San Antonio, says DCIS consists of cancer cells that are inside the milk ducts.

Doctors cannot be sure if it will spread -- or if the patient needs to be treated with radiation or mastectomy.

Today's study, presented at a major breast cancer conference in San Antonio, finds that a genetic test called Oncotype Dx  can help with decisions about how to treat these cases. It gives a score, indicating how high the risk is.

Dr. Kathy Miller, a cancer expert at Indiana University School of Medicine, calls this "huge news" for women: “It allows us to make individualized treatment decisions.”

These results are part of a big movement to try to use genetic markers to tailor the care to each patient.

Experts say only about one-quarter of DCIS patients need radiation.

"Now we can look and say what is your specific risk?  Are you in the three-fourths who have a very low risk,” said Dr. William Wood, a cancer surgeon at Emory University School of Medicine.

This finding could give useful guidance for tens of thousands of women every year.