Anatomy of the Breast

Anatomy of the Breast

What does the inside of the breast look like? This illustration shows the makeup of breast anatomy both inside and outside.

What does the inside of the breast look like? This illustration shows the makeup of breast anatomy both inside and outside.

What’s inside your breasts? Most people aren’t really sure, but if you want to understand breast cancer prevention, risk, or diagnosis, it’s important to know the kinds of tissue and structures breasts are made of. This information will help you visualize what parts of the breast your doctor is referring to. If you have been diagnosed with breast cancer, knowing this will help you talk to your doctor about surgery and other treatment options.

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What is a breast made of?

If you were assigned female at birth, your breasts contain different types of tissue:

  • glandular tissue, which includes the breast lobes and breast ducts
  • fibrous, or supportive or connective tissue, which is the same tissue that ligaments and scar tissue are made of
  • fatty tissue fills in the spaces between glandular and fibrous tissue and largely determines your breast size

Doctors refer to all non-fatty tissue as fibroglandular tissue. There are also bands of supportive, flexible connective tissue called ligaments, which stretch from the skin to the chest wall to hold the breast tissue in place. Muscle plays an important role too. The pectoral muscle lies against the chest wall underneath both breasts, giving them support. Blood vessels provide oxygen to the breast tissue and carry away waste.

What are breast lobes and breast ducts?

Embedded in the breast’s fatty and fibrous tissue are 15 to 20 glands called lobes, each of which has many smaller lobules, or sacs, that produce milk. Lobules are arranged in clusters, like bunches of grapes.

Ducts are thin tubes that carry milk to the nipple. The nipple is located in the middle of the areola, which is the darker area surrounding the nipple. Breast cancers can form in the ducts and the lobes.

Learn more about where breast cancer begins.

What are lymph nodes?

Lymph nodes are small, bean-shaped organs that help fight infection and are found throughout the body. They produce and filter a colorless fluid called lymph, which contains white blood cells known as lymphocytes (immune cells involved in defending against infections and such diseases as cancer).

Lymph vessels filter and carry lymph fluid from the breast to the lymph nodes. Clusters of lymph nodes near the breast are located in the armpit (known as axillary lymph nodes), above the collarbone, in the neck, and in the chest.

What does a mammogram show? 

A mammogram is a test that uses low-dose x-rays to show the inside of your breast. A radiologist (a physician trained to interpret mammography and other images) can identify abnormal areas, masses, or calcium deposits (microcalcifications) that may or may not be cancerous. The greater the detail on the image, the more likely it is that doctors can spot unwanted changes at an early stage, before potentially cancerous cells have a chance to grow or spread. Mammograms done in women with no breast complaints to look for early cancer are called screening mammograms. Those done to evaluate symptoms such as a lump or nipple discharge are diagnostic mammograms. In addition to mammograms, ultrasound and MRI may also be used to take a closer look at changes in the breast.

Learn more about screening for breast cancer.

What are dense breasts?

It is very common for people to be told that they have dense breasts after a mammogram. Dense breasts are completely normal and tend to be more common in younger people and in people with smaller breasts. But anyone — regardless of age or breast size — can have dense breasts.

A doctor will tell you that your breasts are dense if most of the tissue seen on your mammogram is fibrous or glandular breast tissue. These tissue types appear thicker and denser than fatty tissue and will show up white on a mammogram. Because cancer cells also appear white on the image, it may be harder for radiologists to see disease in people with dense breasts. So that’s why some people with dense breasts may be asked to have extra imaging tests, such as ultrasound or MRI, which can pick up some cancers that may be missed on a mammogram.

Learn more about screening guidelines.