(However, postmenopausal women on estrogen replacement therapy may have similar difficulties [Laya et al., 1996], and the number of women on such therapy has been increasing.) This tissue density can make mammograms more difficult to interpret and can thus lead to missed diagnoses, as well as increased rates of false-positive findings (resulting in unnecessary biopsies). One study found that the accuracy of screening mammography in premenopausal women varies with the phase of a woman’s cycle at the time of screening (White et al.,  1998),  suggesting that accuracy might be improved by scheduling the mammogram during a particular phase (the follicular phase during the first 2 weeks of the cycle), but this is not standard practice at present.  Physical examination (CBE and BSE) may also be impeded by dense breast tissue (Heimann et al., 1998).

Other screening modalities that are not affected by breast density might be helpful for the screening of women with dense tissue at any age, especially since there may actually be a correlation between breast density and cancer risk (Byng et al., 1998).

Younger women also tend to have a faster average cell growth rate, meaning that interval cancers may be more common and,  thus,  that screening may need to be conducted more frequently (e.g., annually or, among high-risk women, perhaps even semiannually) to be effective for women in this age group (Kerlikowske et al., 1996; Tabar et al., 1999).

These concerns associated with the screening of younger women are especially relevant to women at high risk.  For example,  women with inherited mutations in breast cancer susceptibility genes such as BRCA1 and BRCA2 are faced with the decision of choosing between prophylactic bilateral mastectomy or screening, often beginning at an earlier age than the general population (Burke et al., 1997). Women may also opt to participate in chemoprevention trials. Thus far, there are no definitive data to guide the decision-making process.  Because of the limitations of mammography, especially for younger women, improved screening methods are seriously needed for this high-risk group. Several institutions are now studying whether alternate screening modalities,  such as MRI or ultrasound, may be more effective and cost-effective for this relatively small, specific group.
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Sharyl J. Nass, I. Craig Henderson, and Joyce C. Lashof
Committee on Technologies for the Early Detection of Breast Cancer

National Cancer Policy Board INSTITUTE OF MEDICINE and Division of Earth and Life Studies
NATIONAL RESEARCH COUNCIL