A new study published in the New England Journal of Medicine is good news for women with early-stage breast cancer.

Researchers say that running a genetic test on a sample tumor can identify women who can safely skip chemotherapy. Those patients would instead only need to take a drug that blocks the hormone estrogen. Such treatments, called endocrine therapy, have become more commonly used in treating women with breast cancer due to lower risk of recurrence, new tumors and death.

The study does note that some women under the age of 50 may benefit from chemotherapy, even if gene testing indicates otherwise. The reason for that is unclear.

Experts expect more than 200,000 new cases of breast cancer in women in the United States this year.

The test in question, the Oncotype DX Breast Cancer Assay, is performed on tumor samples after surgery. It provides doctors with a score between 0 and 100 as a gauge of the activity of specific genes involved in cancer recurrence.

Previous research recommended chemotherapy for any patient with a score of higher than 25 and no chemotherapy for patients with scores under 10. Most women, however, have scores between those two figures, which raises questions as to whether those patients should go through chemotherapy.

Chemo entails side effects that can include heart and nerve damage, and it may also leave patients vulnerable to infections.