The ABCDs of Breast Density: What Is It? Could Dense Breast Tissue Increase the Risk of Cancer?

Joseph R. Anticaglia, MD
Medical Advisory Board

Breast cancer is the second common cancer in the United States after skin cancer. It’s more common than lung, prostate, or colorectal cancers. It accounts for 14% of cancers in the U. S. with 300,900 new cases anticipated in 2023 according to the National Cancer Institute.

Early diagnosis, and treatment are keys to successful outcomes in women with breast cancer. The Food and Drug Administration on March 9, 2023, published updates requiring mammography facilities to notify patients about the density of their breasts. The FDA’s encourages patients to be more aware of breast density, breast mammography reports, and the potential of breast cancer being hidden by dense breast tissue.

“Today’s action represents the agency’s broader commitment to support innovation to prevent, detect and treat cancer,” said Hilary Marston, M. D., M. P. H., FDA’s Chief Medical Officer.

Credit Shutterstock free image Female Breast Anatomy

Anatomy of the Breast

The breasts contain fatty, glandular, and fibrous connective tissues.

  • Fatty (Adipose) tissue largely determines your breast size. It fills in the spaces between the glandular, and fibrous connective tissue
  • Glandular tissue includes the breast lobules which make milk, and ducts which carry milk to the nipple.
  • Fibrous connective tissue supports, and holds your tissues, and muscles in place.. Both glandular, and fibrous connective tissue appear white on a mammogram.

Dense breast tissue, as seen on a mammogram, has more fibrous connective tissue and glandular tissue, and less fatty tissue. It is often inherited, but menopausal hormone therapy, and low body mass index are factors associated with breast density. Dense breast tissue is a risk factor for breast cancer, and a radiologist can tell if a woman has dense breasts.

mammogram uses X-rays (ionizing radiation) to create images of the inside of the breast to check for cancer and other conditions. It can be used for screening to detect cancer, for instance, before there’s a lump in the breast, or to assist in the diagnosis of cancer. Radiologists use mammograms to interpret, and classify breast density into four categories.

A, B, C, D’s of Breast Density and Mammograms

Credit WHO

Category A: Breast tissue is almost all fatty tissue. About 10% of women have this finding. Credit WHO

Category B: There are scattered areas of dense glandular, and fibrous tissue (seen as white areas on the mammogram).The majority of tissue in this category is fatty tissue. About 40% of women have this finding. Credit WHO

Category C: Credit WHO More of the breast is made of dense glandular and fibrous tissue (described as heterogeneously dense). This can make it hard for the radiologist to see small masses in or around the dense tissue, which also appear as white areas. About 40% of women have this finding. Credit WHO

Category D: Breasts are extremely dense which makes it more difficult to identify masses or other findings that may appear as white areas on the mammogram. About 10% of women have this finding. Credit WHO

Dense breasts are common findings after a mammogram, and are not considered a disease, or an abnormal condition. However, they are a risk factor for a woman to develop breast cancer. According to doctors at Memorial Sloan Kettering, women with extremely dense breast tissue “are four to six times more likely to get breast cancer than people with the least dense breasts.”

If a mammogram indicates dense breast tissue, discuss the findings with your physician to better understand what steps the both of you should take to minimize the development of breast cancer. Your doctor may advise additional screening, or diagnostic tests for you.


  1. American Academy of Dermatology; Skin Cancer; April 22, 2022
  2. National Cancer Institute; Common Cancer Types; March 7, 2023
  3. Siegel RL; Cancer statistics; CA: A Cancer Journal for Clinicians 2023; Wiley Online, Updated: March 7, 2023
  4. American Cancer Society; Breast Density and Your Mammogram Report, March 10, 2022
  5. Memorial Sloan Kettering Cancer Center; Anatomy of the Breast; FDA; Updates\Mammography Regulations to Require Reporting of Breast Density Information and Enhance Facility Oversight; March 9, 2023
  6. WHO Images for Normal, and Abnormal Breast Mammography
  7. Dense Breast Tissue and Cancer Risk What You Should Know; Memorial Sloan Kettering; September 7th, 202


A mammogram is an image study of the breast

NCI — National Cancer Institute

ACS — American Cancer Society

Mammography Quality Standards Act (MQSA) of 1992, is a law passed to ensure quality mammography carried out at different mammography facilities in the U. S. The recent action by the FAA in March of 2023 amends MQSA.

This article is intended solely as a learning experience. Please consult your physician for diagnostic and treatment options.