A new medical study says that 70 percent of women diagnosed with one of the most common forms of breast cancer may not need chemotherapy treatment.

The New England Journal of Medicine published a study on Sunday that examined a popular genetic test that estimated cancer risk based on almost two dozen genes linked with the recurrence of breast cancer, according to CNN.

“These data confirm that using a 21-gene expression test to assess the risk of cancer recurrence can spare women unnecessary treatment if the test indicates that chemotherapy is not likely to provide benefit,”  Dr. Joseph A. Sparano, the study’s lead author and associate director for clinical research at the Albert Einstein Cancer Center, said in a statement to CNN.

Dr. Otis Brawley, chief medical and scientific officer for the American Cancer Society said that he was “delighted” by the study and worried about unnecessary cancer treatment and the side effects that come from chemotherapy.

Now with these genomic tests, we are finding that we have multiple types of breast cancer, perhaps several dozen,” Brawley said. “and we are being able to tailor our therapies to the type of breast cancer every woman has.”

There were 1.7 million new breast cancer cases in 2012, according to the World Cancer Research Fund International, making it the most common form of cancer in women globally.

Click here to read the comprehensive study.