Gross Anatomy of the Breast and Axilla
Understanding normal breast structures makes examination reports, scans, and surgical decisions easier to follow.
The key things to know
- Breast size does not determine cancer risk.
- Swollen lymph nodes have several possible causes.
- Breast and lymph-node operations are planned separately.
Inside the breast
The breast contains milk-producing lobules, ducts that carry milk toward the nipple, supporting tissue, and fat. The skin, nipple, and surrounding areola cover these structures. Breast tissue lies over the chest muscles; the breast itself is not a muscle. Size and shape vary naturally and do not, on their own, tell us whether a breast is healthy.
Why the armpit matters
Lymph vessels carry fluid from the breast toward lymph nodes, including nodes in the armpit, called the axilla. These nodes are part of the immune system. They can enlarge because of infection, vaccination, or other causes as well as cancer. An enlarged node is therefore a reason for assessment, not proof that cancer has spread.
Anatomy and cancer treatment
Many breast cancers begin in cells lining ducts or lobules. Invasive cancer has grown beyond the structure where it started. Surgeons consider the position and extent of a lesion when planning breast conservation, mastectomy, or reconstruction. Lymph-node surgery is a separate decision: removing a breast does not automatically mean every underarm node must be removed.
Knowing your usual appearance
Become familiar with how your breasts normally look and feel. A new lump, persistent skin change, new nipple inversion, or spontaneous bloody discharge should be assessed even after a normal screening mammogram. Bring previous images and reports to the appointment. Your clinician may combine an examination with imaging and, when needed, a tissue sample.
Take these questions to your appointment
- Where exactly is the finding on my scan?
- Does my underarm need additional imaging?
Sources & review
This is original educational content based on the sources below, not reproduced textbook material. Website supervisor: Dr. Nizar Ismail. Individual medical review of this article is pending.
This information cannot replace diagnosis or a personal treatment plan. Consult your care team about symptoms or decisions about your treatment.