Breast Density and Cancer Risk: What Is the Relationship?

Extract

Women with dense breasts have been shown to have a four- to six-fold increased risk of developing breast cancer; only age and BRCA1 and BRCA2 mutations increase risk more.

Breast density is a radiologic phenomenon different from the common notion of density as weight per unit of volume. Breast density is not discernable by palpation but rather relates to the fact that x-rays permeate different types of breast tissue differently.

Each type of breast tissue reacts differently to x-rays. Fatty breast tissue is relatively translucent, allowing x-rays to pass through yielding dark areas on a mammogram. Epithelial and stromal tissues, on the other hand, block x-rays and appear as white areas. Breast lesions are not easily discernible in these areas since dense tissue and tumors both look white on film.

Understanding how dense breasts affect cancer risk remains a problem of standardization, said Celia Byrne, Ph.D., Harvard Medical School, Cambridge, Mass. No one method of measuring breast density has been agreed upon.