Most deaths from breast cancer occur in younger women who do not receive regular mammograms, according to a study.
Published Sept. 9 on the website of Cancer, a peer-reviewed journal of the American Cancer Society, the study indicates regular screening before age 50 should be encouraged.
The use of mammograms to prevent breast cancer deaths has been controversial, especially after the United States Preventive Services Task Force proposed in 2009 to limit screening to women ages 50 to 74. Studies show varying benefits, and advances in treatment may have diminished the importance of early detection, according to background information in the study.
Blake Cady, MD, professor of surgery (emeritus) of Harvard Medical School in Boston, and colleagues set out to provide more definitive information on the value of mammography screening through a technique called failure analysis. Such analyses look backward from death to discover correlations at diagnosis, rather than looking forward from the start of a study. Only one other failure analysis related to cancer has been published to date, according to a news release.
In the latest analysis, invasive breast cancers diagnosed at Partners HealthCare hospitals in Boston between 1990 and 1999 were followed through 2007. Data for the study included demographics, mammography use, surgical and pathology reports, and recurrence and death dates.
Among 609 confirmed breast cancer deaths, 29% were among women who had been screened with mammography, compared with 71% among unscreened women. Of all breast cancer deaths, only 13% occurred in women ages 70 and older, while 50% occurred in women younger than 50. Among women diagnosed with breast cancer, the median age of those who died of the disease was 49 at diagnosis; for those dying of any other cause, the median age at diagnosis was 72.
The biological nature of breast cancer in young women is more aggressive, while breast cancer in older women tends to be more indolent, Cady said in the news release. This suggests that less frequent screening in older women, but more frequent screening in younger women, may be more biologically based, practical and cost-effective, Cady said in a news release.
The study also showed a dramatic shift in survival from breast cancer associated with the introduction of screening. In 1969, about half of women diagnosed with breast cancer had died by 12.5 years after diagnosis. Among the women with invasive breast cancer in this review who were diagnosed between 1990 and 1999, only 9.3% had died.
This is a remarkable achievement, and the fact that 71% of the women who died were women who were not participating in screening clearly supports the importance of early detection, said co-author Daniel Kopans, MD, of Harvard Medical School and Massachusetts General Hospital.
A number of research articles have inaccurately claimed that screenings lead to over-diagnosis, Kopans noted. None of these papers have actually looked at individual women but have used registry data, and this has led to false conclusions. This present paper examines each woman as an individual with direct data on who was screened and which women died of breast cancer. It addresses the question from a different and unique perspective.
Study abstract: http://onlinelibrary.wiley.com/doi/10.1002/cncr.28199/abstract.