UNITED NEWS INTERNATIONAL (UNI) — Many women with early-stage breast cancer might not need chemotherapy.

-That’s according to a new study hailed as the largest breast cancer treatment trial ever conducted.

The study spanned 10 years and collected data on nearly 10,000 women diagnosed with an early-stage form of the most common type of breast cancer.

Researchers studied the tumors from all of these women using a molecular test that maps 21 genes.

This test assigns a score to each tumor that predicts how likely breast cancer is to return after surgery.

The researchers found the women who fell in the medium-risk range and only underwent hormone therapy were as just as likely to be cancer-free years later as the women who underwent both hormone therapy and chemo.

These results — published June 3 in the New England Journal of Medicine — suggest less than one-third of women with this form of breast cancer actually need chemo.