When cells in the breast grow out of control, they form a tumor which is malignant looks like a lump on the breast from the outside. This is called as breast cancer. The extent of to which the tumor has spread can be seen in X-ray scans.

Breast cancer might start from a different part of the breast, but most of the time, it begins in the ducts that carry milk to the nipple. This type of cancer is called as ductal cancers. The malignant cells can also begin to grow in the glands that make milk. This type of breast cancer is called as lobular cancer. A very small number of breast cancer starts from other tissues. These types of cancers are called as sarcomas and lymphomas.

Not all breast cancers appear and can be detected in the form of a lump. Some breast cancer can only be detected by screening mammograms. This helps in detecting breast cancer in earlier stages.

The stages of breast cancer are classified using the TNM system. TNM stands for T tumor size, N lymph node status (the cancer reaches the metastasize when the malignant cells reach the lymph nodes), and M metastases, which defines which part of the body the cancer has spread to.

Based on the TNM system, the following are the stages of breast cancer:

Stage 1A
This is the very initial stage of breast cancer. In this stage, the malignant tumor is 2cm small and has not spread outside the breast.

Stage 1B
This stage could mean that cancer is 2cm small, but a few cancer cells are found in the lymph nodes under the arm. This condition is also called as micrometastasis.

Stage 2A
This stage of breast cancer means that the malignant tumor is larger than 2cms, but no cancer cells are found in the lymph nodes under the arm.

Stage 2B
Stage 2B cancer indicates that the tumor cell is larger than 2cms and one or more cells are found in the lymph node under the arm or near the breastbone.

Stage 3A
This is an intermediate stage of breast cancer wherein the tumor size is more than 5cms and cancer cells might be found in at least 4 lymph nodes.

Stage 3B
The tumor in this stage of breast cancer can be of any size and spread to skin, breast or the chest wall. The cancer cells, in this case, can be found in lymph nodes in the underarms as well as the breastbone.

Stage 3C
The tumor can be of any size, and the cancer cells might have spread to at least 10 lymph nodes including the one in the underarms, below the breast bone or collarbone.

Stage 4
This is the final stage of the cancer where in the tumor and the cancer cells have reached the metastasize. The cancer cells have reached the distant parts of the body including the vital organs such as bones, liver, and brain. If the tumor that caused breast cancer reaches the metastasize stage, that is if it grows and invades the surrounding tissues and other parts of the body, then there is damage to that the organ or the part of the body.