Nearly 155,000 women in the United States are living with metastatic breast cancer (MBC), three-fourths of whom were initially diagnosed with lower-stage disease that progressed to stage IV, based on estimated prevalence data.
The estimates, derived from national breast cancer mortality and survival data, also show positive trends in breast cancer care, especially a doubling of 5-year survival rates among younger women diagnosed with de novo metastatic disease from the 1990s to the 2000s, reported Angela B. Mariotto, PhD, of the National Cancer Institute and her colleagues.
“Despite the progressive and incurable nature of almost all MBC, median survival after diagnosis with metastatic disease has been increasing, resulting in a growing number of women living with MBC in the United States. The increased survival is especially noted for women diagnosed at younger ages,” they wrote in Cancer Epidemiology, Biomarkers, & Prevention (2017 May 18. doi: 10.1158/1055-9965.epi-16-088).
Patients with advanced breast cancer require extensive care and intensive use of medical and other resources, but, until this study, there were no reliable estimates of the number of women actually living with metastatic disease in the United States, the authors said.
To get a clearer picture of the prevalence of advanced breast cancer in the United States, they worked backward from Surveillance, Epidemiology, and End Results data on breast cancer deaths and survival, working on the assumption that each observed breast cancer death is the result of metastatic disease, either in women whose initial diagnosis was stage IV disease (de novo metastatic disease) or disease recurrence with metastases.
They estimated that, in 2013, the most recent year for which there were observed data, the prevalence of metastatic breast cancer was 138,622, and that 38,897 (28%) of survivors were diagnosed with metastatic disease. The remaining 99,725 survivors (72%) were women who were initially diagnosed with stage I-III disease that either recurred or metastasized.
The authors calculated that 50,344 women were diagnosed with de novo metastatic disease in 2013, 12,966 of whom (26%) had de novo metastatic breast cancer and 37,378 of whom had recurrent disease. They projected that, as of Jan. 1, 2017, there are 154,794 women living with metastatic breast cancer in the United States.
They also estimated changes over time in survival and found that, for women diagnosed from the ages of 15 to 49 during the 1992-1994 surveillance period, median survival time was 22.3 months, which improved to 38.7 months during the 2005-2012 surveillance period. The respective survival times for women 50-64 years were 19.1 months and 29.7 months.
For women 15-49 years who were diagnosed with de novo metastatic breast cancer, the 5-year relative survival rates doubled from 18% during 1992-1994 to 36% during 2005-2012.
“Despite a poor prognosis, there is a small but meaningful percentage of these cases who survive 10 years or more. More than 11% of women diagnosed between 2000-2004 under the age of 64 years survived 10 years or more. Younger women diagnosed with de novo MBC have higher survival than women diagnosed at older ages,” Dr. Mariotto and her colleagues wrote.
The investigators pointed to the population size, population-based data, long follow-up, and use of consistent staging definitions over time as study strengths but acknowledged that the study was limited by the absence of population-based estimates of survival following recurrence of metastatic breast cancer.
“To our knowledge, this is the first time that the number of women living with MBC in the United States has been estimated. These estimates provide a new perspective on the population burden of breast cancer and have great potential significance to the research and advocacy community working on behalf of patients with MBC and their families,” the authors wrote.
The study was supported by the National Cancer Institute. The authors reported no relevant financial disclosures.
This article was updated June 5, 2017.