Can Breast Density Predict Breast Cancer?

For some time now, researchers have suspected that there might be a link between the density of a breast’s tissues and the development of cancer in that breast. More details about this phenomenon beyond that, however, have not been deciphered--until now.

Breast density defined

Let me first explain what mammography density is, and how breast density is defined. The density of breast tissue in a mammogram is determined by the proportions of fat, connective tissue, and epithelial tissue that are present within a breast. Breast tissue that has greater amounts of epithelial, connective, and supportive tissue is said to have a higher density, and so will have a higher risk of cancer. What hasn’t been known until now is that different densities of breast tissue are associated with specific tumor characteristics and tumor types.

Can density predict the kind of tumor?

Scientists at Harvard Medical School and Brigham and Women’s hospital in Boston conducted research on more than 1,000 post-menopausal women with breast cancer and a matching control group of 1,800 women without breast cancer. The results, which were published in the July 27 online issue of the Journal of the National Cancer Institute, revealed that tissue density could predict some of the types and characteristics of breast tumors. For example, the researchers found--and this was no surprise--that the risk of breast cancer increased progressively as breast density increased.

This relationship between breast-tissue density and tumor characteristics was stronger for larger tumors than for smaller ones; stronger for higher-grade tumors than for lower-grade ones; and stronger for estrogen-receptor-negative tumors than for those that were estrogen-receptor-positive. The researchers also found a link between ductal carcinoma in situ (DCIS) and invasive breast cancer. Breast-tissue density was not found to be predictive of any other tumor characteristics or types. More research is now underway to learn more about these relationships.

Postmenopausal women

It was important for these researchers to study postmenopausal women, because it means that the breast density of these participants had remained high throughout their lives, even after menopause. (Usually, breast densities are higher in premenopausal women, due to their naturally higher levels of estrogen. For most women, estrogen levels diminish as time marches on, causing a corresponding increase in the amount of fatty tissue.)

A final caveat

The researchers did caution, however, that this stronger association of density with risk might be due in part to a characteristic of mammograms called the “masking effect.” Since cancerous tissue can look quite similar to healthy dense tissue in a mammogram, an already-existing tumor can sometimes be hidden or masked, making the tumor more difficult to detect on screening mammography. In spite of this possible problem of masking, however, density is now considered an important risk factor for breast cancer.