Women whose mammograms reveal denser breasts have a greater risk of developing breast cancer, as well as more aggressive tumors compared to those whose breasts are less dense, researchers from the Harvard Medical School and Brigham and Women’s Hospital, Boston, reported in the Journal of the National Cancer Institute.
Mammographic breast density gives an indication of the proportions of connective tissue, epithelial tissue and fat in the breast. It is a known risk factor for breast cancer, the authors explained.
A woman whose breasts have more epithelial and stromal tissue have higher breast density, and consequently a higher risk of developing cancer. However, nobody was sure until this study, whether higher breast density might be linked to tumor characteristics and tumor type.
Rulla M. Tamimi, Sc.D. and team compared the breast density of 1,042 women with breast cancer and 1,794 healthy controls. All the women were postmenopausal, and matched for age and hormone use.
Not surprisingly, they found that breast cancer risk was closely linked to how dense a woman’s breasts were. They also found an association between denser breasts and the development of larger and higher-grade tumors, as well as estrogen receptor-negative tumors.
There was also a higher risk of developing DCIS (ductal carcinoma in situ) than for invasive tumors for those with denser breasts.
Tumor aggressiveness was not linked to other markers, such as nodal involvement and HER2 status, the authors added.
The authors wrote:
“Our results suggest that breast density influences the risk of breast cancer subtypes by potentially different mechanisms,” they write. “Further studies are warranted to explain underlying biological processes and elucidate the possible pathways from high breast density to the specific subtypes of breast carcinoma.”
Karla Kerlikowske, M.D., of the University of California, San Francisco, and Amanda Phipps, Ph.D., of Fred Hutchinson Cancer Research Center, Seattle, write that a better understanding of the biological links between breast density and tumor subtype could help scientists better understand breast cancer risk and the causes of breast cancer at molecular level.
This is the first large-scale study to detect a stronger link between breast density and ER-negative tumors and positive ones, they added.
However, they caution:
“Masking of a tumor can occur because cancerous tissue and mammographically dense tissue have similar x-ray attenuation, allowing tumors to go undetected on screening mammography examination and progress to a more advanced and aggressive stage before detection.”
Possibly, the interaction of a higher number of stromal and epithelial cells in dense breasts may be contributing to cancer risk, and also more aggressive cancer risk, they added.
They concluded:
“Given that the magnitude of the association with breast density is strong across all breast cancer subtypes and particularly for ER-negative disease, breast density should be included in risk prediction models across tumor subtypes.”
“Mammographic Breast Density and Subsequent Risk of Breast Cancer in Postmenopausal Women According to Tumor Characteristics”
Lusine Yaghjyan, Graham A. Colditz, Laura C. Collins, Stuart J. Schnitt, Bernard Rosner, Celine Vachon, Rulla M. Tamimi
Journal of the National Cancer Institute DOI: 10.1093/jnci/djr225
Written by Christian Nordqvist