A new form of drug drastically improves survival rates of younger women with the most common type of breast cancer, researchers said on Saturday, citing the results of an international clinical trial. The findings, presented at the annual meeting of the American Society of Clinical Oncology in Chicago, showed that the addition of cell-cycle inhibitor ribociclib increased survival rates to 70 percent after three and a half years. The mortality rate was 29 percent less than when patients, all under 59 and pre-menopausal, were randomly assigned a placebo. Lead author Sara Hurvitz told AFP the study focused on a form of breast cancer which is fueled by the hormone estrogen and which accounts for two-thirds of all cases among younger women. The treatment is less toxic than traditional chemotherapy because it more selectively targets cancerous cells, blocking their ability to multiply.