Q: What is breast density and how does it affect breast health?

A: Women in Pennsylvania who undergo mammography receive a letter that indicates their breast density, but there is widespread confusion about what the information means. Understanding breast density is easier when we consider breast anatomy and development. Breasts are composed of an arrangement of glandular tissue, fibrous connective tissue, and fatty tissue.

All women are born with varying amounts of these tissues, which will change throughout their lives as they go through such life cycles as puberty, pregnancy, lactation, and menopause. Breast density can be affected by different factors including age, genetics, body fat percentage, and hormone replacement therapy.

Specifically, breast density refers to the relative amount of fibro-glandular tissue and fatty tissue seen on mammographic breast imaging. Breast density is determined by a radiologist, who reads mammograms and looks for certain findings such as calcifications, densities, asymmetries, or distortion that may warrant increased surveillance, additional diagnostic imaging, or a breast biopsy.

Most mammogram reports will describe the patient’s breast density as determined by the radiologist. This is reported using the Breast Imaging and Data System (BI-RADS), which classifies breast density in one of the following ways:

  • A – Almost entirely fatty (about 10% of patients)

  • B – Scattered areas of fibro-glandular density (about 40% of patients)

  • C – Heterogeneously dense (about 40% of patients)

  • D – Very dense (about 10% of patients)

The first two groups (A & B) are not actually considered dense, while the last two groups are. It’s important to know about breast density because having dense breasts can limit the reliability of screening mammography and potentially impact a radiologist’s ability to detect microcalcifications, small densities, and other abnormalities on mammograms, which may represent suspicious changes or early-stage cancers.

It is still the case, however, that many breast cancers are detected on mammographic imaging, even in women with dense breasts. Because of this, screening mammograms are still recommended in women with heterogeneously dense and very dense breasts.

Patients with dense breasts and an abnormal screening mammogram, or new breast symptom, may be recommended for additional diagnostic studies such as ultrasound or breast MRI. It is important to be aware that these studies also detect nonmalignant breast disease, which, if found, may result in additional testing and associated stress.

I encourage women to discuss their individual risk factors with their primary-care provider, OB/GYN, or a breast specialist to see whether they recommend additional imaging or increased surveillance. Each woman’s body is unique, so it is best to talk with your doctor if you have any concerns about your breasts.

Francesca M. Delach is a breast surgeon at Abington-Jefferson Health.