A controversy that has alternately simmered and boiled for more than 40 years reached a flash point this week when the U.S. Preventive Services Task Force published recommendations for breast cancer screening with mammography. The recommendation to delay routine screening in average-risk women until age 50 brought out ardent supporters on both sides of the issue, as reflected in coverage by MedPage Today and in consumer and professional media from coast to coast.
Although media coverage might have created the impression of a new controversy, the strong, conflicting opinions go back at least as far as 1969, when initial results of the first large-scale breast cancer screening program were announced. Data from the Health Insurance Plan (HIP) of Greater New York, published in the Journal of the American Medical Association in 1971, showed a 30 percent reduction in breast cancer deaths in women ages 40 to 64 who underwent clinical breast examination and screening mammography.
With longer follow-up, the HIP data suggested the benefits of screening in terms of reducing death in women was limited to women ages 50 and older. By 1977, the authors of that study had concluded that women ages 40 to 49 did not benefit from screening.
Shortly afterward, a Swedish study published in 1981 in the journal Radiology demonstrated a beneficial effect of breast cancer screening in women ages 40 to 74. In contrast to the HIP data, follow-up for as long as 20 years showed lower deaths in women ages 40 to 49, as well as older age groups, according to a 2003 Lancet study.
Several other studies reinforced the value of breast cancer screening, and mammography gained widespread acceptance among physicians and scientists alike. However, disagreements persisted about the purported benefits of screening in younger women and about the appropriate screening interval.
A 1992 Canadian study published in the Canadian Medical Association Journal added fuel to the controversy by showing an increased death risk in women ages 40 to 49 who underwent mammographic screening. However, subsequent research in 1994 showed that study suffered from a design flaw common to screening studies conducted up to that time: insufficient statistical power to demonstrate a benefit in younger women.
In December 1993, the National Cancer Institute issued a statement clarifying its view on screening mammography. NCI officials concluded that mammography had demonstrated clear benefits for women ages 50 and older, but that the benefits in younger women remained controversial, as studies had not demonstrated a statistically significant reduction in mortality for that age group.
On the basis of the existing data, NCI withdrew its recommendation for mammographic screening every one to two years for women ages 40 to 49. The move brought NCI in line with recommendations from the American College of Physicians and the U.S. Preventive Services Task Force.