Breast density, rapid tumor growth contribute to mammogram failure in women in their forties

Lower sensitivity of mammography in women aged 40 to 49 years compared with older women can be largely explained by greater breast density and rapid tumor growth in the younger women, according to a new study in the October 6 issue of the Journal of the National Cancer Institute.

Because mammography is imperfect for women in their 40s, there has been controversy over whether and how often these women should be screened. Mammographic sensitivity–that is, the percentage of cancers detected by a mammogram–is lower in this group of women than in older women. Several factors have been suggested as contributing to the lower mammographic sensitivity, including higher breast density, faster tumor growth rate, and differences in the distribution of breast cancer risk factors.

To analyze the relative contributions of these factors to differences in mammographic sensitivity between younger and older women, Diana S. M. Buist, Ph.D., of Group Health Cooperative in Seattle, and colleagues studied 576 women (73 aged 40 to 49 years and 503 aged 50 years and older) who were diagnosed with invasive breast cancer between 1988 and 1993. They looked at associations between potential explanatory factors and the odds of having an interval cancer (cancer diagnosed within 12 or 24 months after a negative screening mammogram and before a subsequent mammogram).

Interval cancers occurred in 27.7% of the younger women and 13.9% of the older women within 12 months of a screening mammogram and in 52.1% of younger women and 24.7% of older women within 24 months. Greater breast density–which has been shown to reduce mammographic quality–explained 67.6% of the decreased mammographic sensitivity in younger women at 12 months. Rapid tumor growth explained 30.6% and greater breast density explained 37.6% of the decreased sensitivity in younger women at 24 months. The authors suggest that screening younger women at yearly intervals may reduce the adverse impact on mammographic sensitivity of rapid tumor growth that occurs in young women.

“There are 21.7 million women in the United States aged 40–49 years, approximately 50% of whom have dense breasts,” the authors write. “It may be that digital mammography, computer-aided detection, magnetic resonance imaging, and/or ultrasound can improve cancer detection in women with dense breast tissue.”