Method To Determine Age Individual Women Should Begin Mammogram Screening

National Cancer Institute
Friday, 28 August 1998

A paper in the September issue of the Journal of Clinical Oncology by two investigators from the National Cancer Institute (NCI), Mitchell Gail, M.D., Ph.D., of the Division of Cancer Epidemiology and Genetics and Barbara Rimer, Dr.P.H., of the Division of Cancer Control and Population Sciences, provides two methods to assist women and their physicians in making a decision about when to initiate regular mammograms. *

Several organizations, including NCI and the American Cancer Society, have recommended that women in their 40s have regular mammograms. There are, however, some costs and side-effects from mammography, including the need to follow up on suspicious results with more tests, such as repeat mammograms and, in some cases, biopsies. Thus, some women and their physicians may want to make decisions about when to begin regular mammograms based on the woman's individual risk of developing breast cancer.

To make an individual risk assessment for breast cancer, a woman in her 40s and her doctor must first determine whether any of the following six risk factors are part of her medical history:

- previous breast cancer;

- specific alteration in a breast cancer susceptibility gene such as BRCA1 and BRCA2;

- a mother, sister, or daughter with breast cancer;

- atypical hyperplasia (a condition where breast cells are both abnormal in appearance and increased in number) on previous breast biopsy;

- 75 percent dense tissue on mammogram at age 45-49; or,

- two or more breast biopsies, even if the results are benign.

If any of these factors are present, according to the paper by Gail and Rimer, risk is high enough to warrant screening for a woman in her 40s. If none are present, three weaker factors still need to be considered:

- age of menarche;

- the number of previous breast biopsies (either zero or one); and,

- age at their first live birth (the risk for breast cancer for a women with no live births is the same as a women who had a child at ages 25-29).

The paper describes two methods to help a woman and her doctor do this. The first provides self-explanatory flow charts for black and white women that lead to screening decisions. The second requires a calculation that takes the weaker factors into account and then compares a woman's relative risk for breast cancer to that of a 50-year-old woman with no risk factors.

No matter which method is used, mammography is recommended if a woman's projected risk of developing breast cancer is greater than that of a 50-year-old woman with no risk factors.

Because the incidence of breast cancer in black women in their 40s rises more rapidly than in white women, fewer risk factors are required for screening recommendations for black women than white women. For example, for a 41-year-old black woman with none of the six stronger risk factors, who began menarche at age 13, had one breast biopsy and one child at 19, screening would be recommended. For a white woman with the same risk factors, delaying screening is an option.

Using these methods, the authors estimated that 10 percent of white women age 40 would be recommended for screening compared to 95 percent of white women age 49. The corresponding numbers for black women are 16 percent and 95 percent. Making certain assumptions, the methods can also be used for Hispanic and Asian/Pacific Island women.

It is hoped that the availability of this individualized risk information may serve an important point of departure for a thorough, open discussion of a woman's particular risks and preferences with her health care provider. These methods can also be used as an educational tool for women who do not have access to expert guidance and for the large proportion of women who either underestimate or overestimate their risk. For example, women who are reluctant to be screened may choose screening once they have been provided with information about their own risk. Other women who have high levels of anxiety about breast cancer risk may find personalized risk information reassuring, and may defer screening for one to two years.

The risk model in this paper was based on a study of mammographic screening in over 280,000 women who participated in the Breast Cancer Detection Demonstration Project in the 1970s. The paper also reviews the data indicating a survival benefit for women in regular mammography screening in their 40s and justifies the comparison with the benchmark 50-year-old woman in terms of the health risks and benefits of mammography screening.

*The study is titled "Risk-Based Recommendations for Mammographic Screening for Women in their Forties." The authors are Mitchell H. Gail and Barbara K. Rimer. Journal of Clinical Oncology, Vol. 16, No. 9. September 1998.

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