Cancer occurs when abnormal cells form and divide uncontrollably in areas of the body, often destroying the body's healthy tissue. According to the MayoClinic.com, cancer is the second leading cause of death in the United States. Common forms of cancer include lung, breast, prostate, colon and skin cancer. Doctors typically use a five-stage scale to describe how advanced certain cancers are. Staging is also used to determine treatment associated with various cancers. Staging, as defined by the National Cancer Institute, also refers to the size and spread of specific cancer in the body. The American Cancer Society describes the "TNM" classification system as an increasingly popular way to determine the severity of individual cancers using specified stages. Each cancer is assigned a stage for T, or tumor; N or spread into lymph nodes; and M, or metastases, if the cancer has spread.
Stages Associated with Tumor
The stage of tumor refers to the size of the actual tumor, and is rated on a zero to IV stage. Stage zero, or T0, is the earliest stage and refers to a tumor that has not yet started to attack healthy tissue and cannot be evaluated. "Tis," or "carcinoma in situ," according to the National Cancer Institute, is the next stage and is used to describe cancer that has not yet spread. The stages of tumor are then represented by the letter "T" and a number indicating the size and seriousness associated with the tumor: T1 being the least severe to T4 being the most serious.
Stages of Lymph Node Involvement
The "N" in the TNM classification system refers to the degree of localized lymph node association. When lymph nodes are involved in the cancer diagnosis, the disease is considered to be very serious and represented with a number reflecting such. Like the stages of tumor, a zero, represented as N0, means no lymph node involvement. Stages such as N2, N3, or N4, representing the most serious stage of lymph-node involvement, usually indicates an increased probability that more than one lymph node area is involved.
Metastasis
Although cancer usually starts in one area of the body, called the "primary" tumor, the cancer cells can move elsewhere in the body; this process is called "metastasis." The process of metastasis often occurs through the lymph nodes. Although cancer may spread to other parts of the body, it is still considered cancer of the initial area of tumor growth. Lung cancer that has spread to the liver does not become liver cancer, rather metastatic lung cancer.
Stages of Cancer Associated with Distant Metastasis
Unlike the staging associated with tumors or lymph node involvement, stages of distant metastasis are represented in two ways, "M0" and "M1." M0 indicates that the cancer is localized and has not spread to other parts of the body. M1 is more serious of the two stages and indicative of a cancer that has spread to other areas of the body.
