Breast Cancer Screening: New Fuel for an Old War of Words and Data

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.

Younger Women Become Focus

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.

A New Round of Controversy

The NCI decision touched off another philosophical firestorm. The American Cancer Society (ACS), American College of Radiology (ACR), and American College of Obstetricians and Gynecologists (ACOG) all reaffirmed their support for regular mammographic screening of women starting at age 40. That view had emerged from an ACR-sponsored consensus conference involving 12 medical organizations.

Another major contribution to the screening controversy came in 1995 with the publication of a review of eight clinical trials of breast cancer screening with mammography, published in the Journal of the Medical Association. The analysis found no evidence of a mortality reduction in women ages 40 to 49 with screening mammography.

Another analysis, also published in 1995 but in the journal Cancer, showed a statistically significant 24 percent reduction in breast cancer mortality in the 40-to-49 age group when data from the Canadian study were excluded. Inclusion of the Canadian data resulted in a nonsignificant mortality reduction.

Consensus Sought on Mammmograms

Seeking to clear up uncertainty about the benefits of breast cancer screening in younger women, NCI held a consensus conference in early 1997. Many of the key players in the controversy from 1969 to the present participated in the conference, either as a panelist or speaker. Presentations and discussions focused only on the 40-to-49 age group.

Initially, the 13-member consensus panel reached a unanimous agreement about the conclusions and wording. After reading the draft consensus statement, two panelists disagreed with the document's language. When the panel could not reach a unanimous consensus, the final document included majority and minority opinions.

The majority opinion stated that "the data currently available do not warrant a universal recommendation for mammography for all women in their forties. Each woman should decide for herself whether to undergo mammography."

Authors of the minority report decided that the majority report placed that too much emphasis on the potential risks of mammography. The two panelists concluded that the data did support a recommendation for routine mammographic screening for all women ages 40 to 49.

The majority report touched off another round of public debate about the merits of mammography for younger women, including sometimes heated discussions at several professional meetings.

Subsequently, NCI issued a new statement on mammography, supporting screening every one or two years for all women ages 50 and older and screening every one or two years for average-risk women ages 40 to 49.

Still, the controversy would not go away. In 1997, data from another Swedish study published in the journal Cancer showed that mammographic screening of women ages 39 to 49 every 18 months reduced the mortality risk by 44 to 45 percent. An accompanying editorial included a reanalysis of the original Swedish study and showed a statistically significant mortality reduction in patients ages 40 to 49 when screened annually rather than biennially.

Enter the New Millennium

Another war of words ensued following publication in 2000 of statistical analyses by Scandinavian representatives of the Cochrane Collaborative. In short, two authors concluded in the journal Lancet that mammography does not save lives and exposes women to unnecessary surgical procedures.But a 2004 examination of the Scandinavians' methods showed that the authors reached their conclusions by excluding from analysis all positive studies, which they dismissed as being of poor quality.

Whether the controversy ever reaches a resolution remains anyone's guess at this point. For the time being, proponents of routine screening for younger women appear to have the upper hand. ACS, ACOG, and ACR have all reaffirmed their support, and NCI issued a statement that the agency's position on mammography remains unchanged.

Health and Human Services secretary Kathleen Sebelius issued what might be considered the final word -- at least for the time being.

Noting that the Preventive Services Task Force does not make health policy, Sebelius urged women to "keep doing what you have been doing for years -- talk to your doctor about your individual history, ask questions, and make the decision that is right for you."