According to the National Cancer Institute, each year more than 192,000 women are diagnosed with breast cancer. Merck Manuals, an online medical library, reports that breast cancer is the second-most common type of cancer and the second-most common cause of cancer death. The Mayo Clinic reports that breast cancer can be defined by its stage of development, which can help to determine the possible treatment options. Stages are determined based upon tumor size, and whether and how far it has spread within the body.
Stage 0
Stage 0 is the earliest stage of breast cancer. According to Merck Manuals, the tumor, and thus the cancerous cells, are present only in the breast. The tumor usually is within the milk duct or the gland that produces milk, and has not spread throughout the breast.
Stage 1
The National Cancer Institute describes Stage 1 breast cancer as when the cancerous cells have spread throughout the breast beyond the specific place of origin but are not found outside the breast. Merck Manuals adds that the tumor is small, fewer than 3/4 inches in diameter.
Stage 2
The National Cancer Institute reports that generally, breast cancer is said to be in Stage 2 when the tumor is larger than 3/4 inches or has spread to the lymph nodes under the arm. Merck Manuals notes that Stage 2 can be divided into two stages: 2A and 2B. Stage 2A is classified as when the tumor is smaller than 3/4 inch, and a small amount of cancerous cells have spread to nearby lymph nodes, or it is between 3/4 and 2 inches but has not spread to nearby lymph nodes. Stage 2B is classified as when the tumor is larger than two inches, whether or not it has spread to nearby lymph nodes.
Stage 3
Stage 3 breast cancer is also divided into sub-stages: 3A, 3B and 3C. The National Cancer Institute and Merck Manuals describe Stage 3A as when the tumor has spread to four to nine lymph nodes, or spread to the lymph node behind the breastbone. Stage 3B is when the tumor has spread to the skin or chest wall, or has started to cause inflammation in the breast. Stage 3C is defined by the National Cancer Institute and Merck Manuals to be any size, and is unique in the way the cancerous cells have spread. The tumor has spread to: many (10 or more) lymph nodes in the arm, lymph nodes near the collarbone, or lymph nodes in the armpit and breast bone lymph nodes.
Stage 4
Stage 4 is the latest stage of breast cancer. The National Cancer Institute and Merck Manuals report that Stage 4 breast cancer is characterized by a tumor of any size that has spread from the breast to distant sites in the body. The cancerous cells may invade the liver, lungs, bones or other tissues. Cancer that has spread this much is called metastatic cancer.
