Cancer occurs when changes called mutations take place in genes that let the cells divide and multiply in an uncontrolled way.
Breast cancer is cancer that develops in breast cells when it forms in either the lobules or the ducts of the breast. Lobules are the glands that produce milk, and ducts are the pathways that bring the milk from the glands to the nipple. Cancer can also occur in the fatty tissue or the fibrous connective tissue within your breast.
The uncontrolled cancer cells often invade other healthy breast tissue and can travel to the lymph nodes under the arms. The lymph nodes are a primary pathway that help the cancer cells move to other parts of the body.
In its early stages, breast cancer may not cause any symptoms and the tumor may be too small to be felt, but an abnormality can still be seen on a mammogram. If a tumor can be felt, the first sign is usually a new lump in the breast that was not there before.
Symptoms for the most common breast cancers include:
- a breast lump or tissue thickening that feels different than surrounding tissue and has developed recently
- breast pain
- red, pitted skin over your entire breast
- swelling in all or part of your breast
- a nipple discharge other than breast milk
- bloody discharge from your nipple
- peeling, scaling, or flaking of skin on your nipple or breast
- a sudden, unexplained change in the shape or size of your breast
- inverted nipple
- changes to the appearance of the skin on your breasts
- a lump or swelling under your arm
Breast cancer can be divided into stages based on how large the tumor or tumors are and how much it has spread.
- if the cancer is invasive or noninvasive
- how large the tumor is
- whether the lymph nodes are involved
- if the cancer has spread to nearby tissue or organs
Breast cancer has five main stages: stages 0 to 5.
Stage 0 breast cancer
Stage 0 Cancer cells in DCIS remain confined to the ducts in the breast and have not spread into nearby tissue.
Stage 1 breast cancer
- Stage 1A: The primary tumor is 2 centimeters wide or less and the lymph nodes are not affected.
- Stage 1B: Cancer is found in nearby lymph nodes, and either there is no tumor in the breast, or the tumor is smaller than 2 cm.
Stage 2 breast cancer
- Stage 2A: The tumor is smaller than 2 cm and has spread to 1–3 nearby lymph nodes, or it’s between 2 and 5 cm and hasn’t spread to any lymph nodes.
- Stage 2B: The tumor is between 2 and 5 cm and has spread to 1–3 axillary (armpit) lymph nodes, or it’s larger than 5 cm and hasn’t spread to any lymph nodes.
Stage 3 breast cancer
- Stage 3A:
- The cancer has spread to 4–9 axillary lymph nodes or has enlarged the internal mammary lymph nodes, and the primary tumor can be any size.
- Tumors are greater than 5 cm and the cancer has spread to 1–3 axillary lymph nodes or any breastbone nodes.
- Stage 3B: A tumor has invaded the chest wall or skin and may or may not have invaded up to 9 lymph nodes.
- Stage 3C: Cancer is found in 10 or more axillary lymph nodes, lymph nodes near the collarbone, or internal mammary nodes.
Stage 4 breast cancer
Stage 4 breast cancer can have a tumor of any size, and its cancer cells have spread to nearby and distant lymph nodes as well as distant organs.