A new study shows that the number of women in the United States living with distant metastatic breast cancer (MBC), the most severe form of the disease, is growing. This is likely due to the aging of the U.S. population and improvements in treatment. Researchers came to this finding by estimating the number of U.S. women living with MBC, or breast cancer that has spread to distant sites in the body, including women who were initially diagnosed with metastatic disease, and those who developed MBC after an initial diagnosis at an earlier stage.

The researchers also found that median and five-year relative survival for women initially diagnosed with MBC is improving, especially among younger women.

The study was led by Angela Mariotto, Ph.D., chief of the Data Analytics Branch of the Division of Cancer Control and Population Sciences at the National Cancer Institute (NCI), with coauthors from NCI, the Metastatic Breast Cancer Alliance, and the Fred Hutchinson Cancer Research Center. The findings appeared online on May 18, 2017, in Cancer Epidemiology, Biomarkers & Prevention. NCI is part of the National Institutes of Health.

In documenting the prevalence of MBC, the findings point to the need for more research into how to address the health care needs of women who live with this condition. “Even though this group of patients with MBC is increasing in size, our findings are favorable,” said Dr. Mariotto. “This is because, over time, these women are living longer with MBC. Longer survival with MBC means increased needs for services and research. Our study helps to document this need.”

Although researchers have been able to estimate the number of women initially diagnosed with MBC, data on the number of women whose cancers spread to a distant organ site, either as a progression or a recurrence after being first diagnosed with an earlier stage of breast cancer, has been lacking because U.S. registries do not routinely collect or report data on recurrence. To develop a more accurate estimate of the total number of women living with MBC, researchers used data from NCI’s Surveillance, Epidemiology, and End Results (SEER) Program to include women who developed MBC after diagnosis. The researchers estimated that, as of Jan. 1, 2017, more than 150,000 women in this country were living with MBC, and that 3 in 4 of them had initially been diagnosed with an earlier stage of breast cancer.

The study also shows that despite the poor prognosis of MBC, survival of women initially diagnosed with MBC has been increasing, especially among women diagnosed at younger ages. The researchers estimated that between 1992- 1994 and 2005 2012, five-year relative survival among women initially diagnosed with MBC at ages 15-49 years doubled from 18 percent to 36 percent. Median relative survival time between 1992-1994 and 2005-2012 increased from 22.3 months to 38.7 months for women diagnosed between ages 15 49, and from 19.1 months to 29.7 months for women diagnosed between ages 50-64. The researchers also reported that a small but meaningful number of women live many years after an initial diagnosis of MBC. More than 11 percent of women diagnosed between 2000-2004 under the age of 64 survived 10 years or more.

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