Efficacy of Screening Mammography
The efficacy of screening mammography in decreasing breast cancer mortality has been demonstrated in numerous studies. In the 1960s, The Health Insurance Plan (HIP) of Greater New York performed a study of physical examination and mammography in a study group of 30,756 women and a control group of 30,239 women age 40-64 years. The study consisted of an initial screening with a two-view mammogram and physical examination plus three annual follow-ups. In the study group, 132 breast cancers were detected. Of these, 33% were detected by mammography alone, 45% by physical examination and 22% by both methods. At 10 year followup, the study had a 30% decrease in breast cancer mortality compared to the control group.
The Breast Cancer Detection Demonstration Project (BCDDP) screened 283,222 women from 1973-1981 in 27 cities in the US with an initial physical examination and two-view mammogram and four subsequent examinations.
No control group was used, but data were compared to the data from Surveillance, Epidemiology, and End Results (SEER) of the National Cancer Institute. Of the cancers detected in the BCDDP study, 42% were detected by mammography alone, 9% by physical examination alone and 47% by both methods. Of the in situ cancers found in the BCDDP study, mammography alone found 59%. Minimal cancer (in situ or infiltrating cancer < 1 cm) made up 33% of the tumors found by mammography. These data, and those of numerous subsequent studies, support the ability of screening mammography to detect early breast cancers and save lives.
There has been recent controversy regarding the use of screening mammography in women under the age of 50. Kopans has pointed out that this controversy has no biological basis, since none of the screening parameters change abruptly at age 50. Individual screening studies have not had sufficient numbers of women to demonstrate a statistically significant decrease in mortality in women under the age of 50. When the data from multiple trials are pooled in a meta-analysis, however, a statistically significant decrease in mortality from screening mammography is demonstrated in women in their 40s. Hendrick et al analyzed eight randomized controlled trials of mammographic screening and found a statistically significant 18% reduction in mortality in women in their 40s; combined data from five Swedish trials yielded a statistically significant mortality decrease of 29%.
Guidelines for Screening Mammography
Currently, the American College of Radiology and the American Cancer Society recommend annual mammographic screening to begin at age 40. The National Cancer Institute recommends mammographic screening every 1 to 2 years for women between the ages of 40 and 50 and annual mammography for women age 50 and older.
Annual screening mammography can commence earlier than age 40 in a few special circumstances.
Women who have had breast cancer or a biopsy diagnosis of lobular carcinoma in situ (LCIS) are screened annually from the time of diagnosis. For women with a first-degree relative (mother or sister) who developed premenopausal breast cancer, annual screening mammography may begin at an age 10 years younger than the age at which her relative developed breast cancer, but no younger than age 25.
For women under age 40 who received mantle irradiation for Hodgkin’s disease, it has been suggested that screening mammography should begin approximately 8 years following completion of radiation.
For women with positive genetic testing for the breast cancer genes BRCA1 or BRCA2, annual mammography is suggested beginning at age 25-35 years, with the specific age chosen based on individual preferences, the adequacy of mammographic imaging in the first study and the feasibility of breast examination.
Laura Liberman and Timothy L. Feng
Breast cancer detection demonstration project: five-year summary report. CA 2003