Most patients suffering from the most common form of early-stage breast cancer do not need to undergo chemotherapy, a new landmark study has found. The study, funded by the National Cancer institute and several philanthropic groups, used genetic testing in the largest study ever conducted on breast cancer treatment. Its findings mean an estimated 60,000 women a year in the U.S. can avoid the ordeal of chemotherapy, according to the leader of the study, Dr. Joseph Sparano of Montefiore Medical Center in New York. “This is very powerful. It really changes the standard of care,” Dr. Ingrid A. Mayer, an author of the study, was quoted as saying by The New York Times. “We can spare thousands and thousands of women from getting toxic treatment that really wouldn’t benefit them,” she said. The study, which began in 2006, was presented Sunday at a meeting of the American Society of Clinical Oncology in Chicago.