WASHINGTON — The number of women living with advanced breast cancer is rising substantially in the United States, reflecting improved survival rates among all ages, according to a study published Thursday.
The study found that between 1992 and 1994, and 2005 and 2012, the five-year survival rate among women under age 50 initially diagnosed with advanced disease doubled to 36 percent, from 18 percent. The median survival time for that group increased to almost 39 months, up from 22.3 months. For women ages 50 to 64, the survival time grew from a little more than 19 months to almost 30 months.
The lead author, Angela Mariotto of the National Cancer Institute, called the findings ‘‘favorable’’ because they were partly due to longer survival times resulting from better treatments. For example, the drug Herceptin, approved in the late 1990s, has been shown to lengthen the lives of women with certain aggressive breast cancers.
The researchers calculated that more than 154,000 women are living with cancer that has spread beyond the breast, the most serious form of the disease.
Mariotto, chief of the Data Analytics Branch in the NCI’s Division of Cancer Control and Population Sciences, said the study didn’t explore why younger women survived longer, but one possibility was that they received more aggressive treatment.
Patients with Stage 4 breast cancer, the most advanced, have the most intensive health care needs, and advocacy groups, providers, and researchers are increasingly interested in knowing how many are affected. The study estimated that the number rose by 4 percent from 1990 to 2000 and by 17 percent from 2000 to 2010. From 2010 to 2020, it is projected to increase by about 33 percent.
Metastatic breast cancer once was considered an immediate death sentence, and it’s still largely incurable, the researchers said. But new therapies targeting the triggers of the disease as well as improved palliative care mean women ‘‘can and often do live for years with reasonable quality of life, albeit undergoing constant treatment to keep their disease under control,’’ they said.
The authors, who included researchers at Fred Hutchinson Cancer Research Center in Seattle and the Metastatic Breast Cancer Alliance, said the study was the first to estimate how many women are living with advanced disease in the United States. Their findings appeared online in Cancer Epidemiology, Biomarkers & Prevention.
To calculate the number of women with metastatic breast cancer, the scientists combined the number of women who were initially diagnosed with advanced disease with those who developed it after being diagnosed at an earlier stage. Such estimates are challenging, they said, because of data gaps in cancer registries.