Higher Cancer Risk and Aggressive Tumors Linked with Greater Breast Density

In the Journal of the National Cancer Institute, researchers from Harvard Medical School and Brigham and Women’s Hospital in Boston reported that compared to women with less dense breasts, those with denser breasts revealed through a mammogram are at a greater risk of developing breast cancer as well as more aggressive tumors.
The authors explained that connective tissue, epithelial tissue, and breast fat proportions indicate Mammographic breast density.

Breast cancer is more prevalent in women with higher breast density (more epithelial and stromal tissue). However, until this study, there was no certainty whether tumor characteristics and tumor type might be linked to higher breast density.

Rulla M. Tamimi, Sc.D. and team studied the breast density in postmenopausal women who were matched for age and hormone. They compared the breast density of 1,042 breast cancer women with 1,794 healthy controls.

As expected, a close association was found between breast cancer risk and the density of women’s breasts. In addition, denser breasts were found to be associated with the development of larger and higher-grade tumors as well as estrogen receptor-negative tumors.

Those with denser breasts were also at a higher risk of developing DCIS (ductal carcinoma in situ) than invasive tumors.

The authors added that markers such as nodal involvement and HER2 status were nowhere linked with tumor aggressiveness.
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.”

Accompanying Editorial

Scientists can gain a better understanding of the risks and causes of breast cancer at a molecular level by enhancing their understanding about the biological links between breast density and tumor subtype, write Karla Kerlikowske, M.D., of the University of California, San Francisco, and Amanda Phipps, Ph.D., of Fred Hutchinson Cancer Research Center, Seattle.

They added that this is the first large-scale study to have established that breast density is strongly linked with ER-negative and positive tumors.

They advised: “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.”

They said that aggressive cancer risk might be enhanced due to a possible interaction of a higher number of stromal and epithelial cells in dense breasts.

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.”

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