Based on their calculations, the researchers estimated that the number of women living with MBC increased by 4 percent from 1990 to 2000 and by 17 percent from 2000 to 2010, and they project that the number will increase by 31 percent from 2010 to 2020. Although the largest group of women with MBC consists of women who have been living with metastatic disease for two years or less (40 percent), one third (34 percent) of women with MBC have lived for five years or more with the disease.

To estimate the number of U.S. women living with MBC, the researchers applied a back-calculation method to breast cancer mortality and survival data from the SEER Program. SEER collects clinical, demographic, and vital status information on all cancer cases diagnosed in defined geographic areas. The method they used assumes that a breast cancer death is preceded by MBC that was either found at diagnosis or after a recurrence with metastatic disease.

Collecting recurrence data has been challenging for cancer registries because recurrence can be diagnosed through diverse methods and in a variety of locations. To help implement the comprehensive and accurate collection of these data, NCI is funding pilot studies aimed at identifying ways to leverage existing data and informatics methods to efficiently capture information on recurrent disease.

"Researchers reported that a small but meaningful number of women live many years after an initial diagnosis of metastatic breast cancer. More than 11 percent of women diagnosed between 2000-2004 under the age of 64 survived 10 years or more."

By including women with recurrence, this study provides a more accurate number of women in the U.S. currently living with MBC. This estimation can help with health care planning and the ultimate goal of better serving these women.

“These findings make clear that the majority of MBC patients, those who are diagnosed with non-metastatic cancer but progress to distant disease, have never been properly documented,” said Dr. Mariotto. “This study emphasizes the importance of collecting data on recurrence at the individual level in order to foster more research into the prevention of recurrence and the specific needs of this growing population.”

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