Women of all ages who are diagnosed with advanced-stage breast cancer in the United States are surviving longer, according to a new study published Thursday. Lead author Angela Mariotto, of the National Cancer Institute, said the findings were largely due to better treatments, including a drug called Herceptin, which lengthens the lives of women with aggressive breast cancers. It was approved in the late 1990s. The study results showed the five-year survival rate among women under 50 years old who were diagnosed with advanced disease doubled from 18 percent in the mid-1990s to 36 percent between 2005 and 2012. Among those with Stage 4 cancer, the study reports five-year survival rates rose by 4 percent from 1990 to 2000, and by 17 percent between 2000 and 2010, with projections of an increase by a third by 2020. More than 154,000 American women are estimated to be living with cancer that has spread beyond the breast.