Mammographic screening for breast cancer and improved breast cancer treatment have both contributed to declining breast cancer mortality rates in the US, according to a study published in the New England Journal of Medicine .
Breast cancer is second only to lung cancer as a leading cause of cancer death in women. Fortunately, survival appears to be improving; the breast cancer mortality rate in the US dropped from 48 per 100,000 women in 1975 to 38 per 100,000 women in 2000. There has been debate about the cause of this decline and disagreement about the role played by screening mammography. A mammogram is an x-ray image of the breast. The goal of a screening mammogram is to detect breast cancer at an early stage, when it is most treatable.
Settling the question about the contribution of screening mammography to declining mortality rates is important. If women and their physicians are going to continue to adhere to breast cancer screening recommendations, they will need to be confident that screening saves lives.
In order to clarify matters, the National Institutes of Health (NIH) funded seven separate groups in the US to estimate the extent to which treatment and screening have each contributed to the decline in breast cancer mortality. The study involved researchers at the Dana Farber Cancer Institute, Erasmus University, Georgetown University, MD Anderson Cancer Center, University of Rochester, Stanford University, and University of Wisconsin-Madison. Each of the groups developed a different statistical model using the same set of data.
Although there was variability in the estimates, all seven groups drew the same conclusion: The decline in breast cancer mortality that occurred in the US between 1975 and 2000 is explained by a combination of screening and treatment-neither factor alone is responsible. Individual estimates about how much of the decline in mortality is due to screening mammography ranged from 28% to 65%, with a median of 46%. The rest of the decline in mortality was attributed to improved treatment.
The researchers conclude that declining breast cancer mortality is due to both earlier detection of breast cancer through screening mammography, as well as improved cancer treatment. This study provides additional support for the use of screening mammography for the early detection of breast cancer.
Reference: Berry DA, Cronin KA, Plevritis SK et al. Effect of Screening and Adjuvant Therapy on Mortality from Breast Cancer. New England
Journal of Medicine. 2005;353:1784-92.