By Chris Parkhurst
(WebMD) -- According to the National Cancer Institute, breast cancer is the most common type of cancer among women in the United States. More than 180,000 women are diagnosed with it annually. In order to understand the diagnosis and treatment of this disease, it's important to clarify the different stages of breast cancer. There are two systems used to represent breast-cancer staging.
Traditional staging consists of four stages. In Stage I, the actual tumor is generally no larger than 2 cm across and cancer cells have not spread beyond the breast. Stage II may comprise any of the following: the tumor is less than 2 cm across and cancer has spread to the lymph nodes; the tumor is between 2 and 5 cm and has or has not spread to the lymph nodes; or the tumor is larger than 5 cm but has not spread to the lymph nodes. With Stage III, also called locally advanced cancer, the tumor is larger than 5 cm and is extensive in the lymph nodes. In Stage IV, or metastatic cancer, the cancer has spread to other parts of the body.
TNM, which is considered to be the most precise system for staging, assesses separately the tumor, lymph nodes and further spread of the cancer. Each letter is followed by a number that further indicates the severity of the problem. For example, someone diagnosed with "T2N1M0" has tumor growth from 2 to 5 cm, which has spread to the lymph nodes but has not metastasized.
T1 signifies that someone has a tumor that is less than 2 cm in size. A tumor that is 2 to 5 cm across is given a T2 status. T3 is a tumor that is larger than 5 cm. Someone diagnosed with a T4 has had the tumor extend to the chest wall or skin.
N0 indicates that no tumor has been found in the lymph nodes underneath the arms. If the tumor has spread to the lymph nodes, but the lymph nodes have not grown together or into other structures, it is called an N1. An N2 indicates that the tumor has spread to the lymph nodes, which have grown together or into other structures under the arm. The N3 status indicates that the tumor has spread to lymph nodes inside the chest.
As is the case with most cancers, breast cancer can metastasize, meaning it can spread to other parts of the body. Among other places it can travel in the body are the lungs, liver, bones, kidneys and heart. The two designations given are M0 and M1. M0 indicates that the tumor has not spread to other organs. M1 shows that the tumor has indeed spread to other organs.