Cancer staging is a process used by doctors to describe the severity of cancer in a specific patient. One of the most commonly used staging systems is called the TNM system, which stages cancer based upon tumor formation (T), lymph node involvement (N) and presence of metastasis (M), explains the National Cancer Institute. If you receive a cancer diagnosis, your doctor will likely recommend further testing to allow her to determine what stage of cancer you have.
The earliest, most treatable forms of cancer are stage 0 cancers—though this staging level is not applicable to all forms of cancer. During this stage, abnormal cells are only detectable within the top layer of cells within the affected body region. Such forms of cancer are often referred to as carcinoma in situ, which means that abnormal cells are only located at the site where they originated. For example, stage 0 breast cancer means that abnormal cells are only detectable within the cells that line the breast duct or lobules.
When abnormal cells clump together and begin penetrating beneath the top layer of cells within the organ of origin, they can form stage I cancer. This stage of cancer describes cancer that is small and present only within the organ of origin. Due to these characteristics, stage I cancer is typically very treatable and has a high cure rate in the majority of cancer patients.
Stage II cancer occurs when cancerous cells begin to grow into a small tumor within the organ of origin. Typically, cancer in this stage has not spread to other tissues or organs within the body. In certain people, cancerous cells that spread into nearby lymph nodes may be classified as stage II cancer.
As the cancerous tumor grows, it can begin to spread into the lymph nodes and surrounding tissues, explain health professionals at Cancer Research UK, the leading cancer research charity in the world. When this occurs, the cancerous tumor is characterized as stage III.
Stage IV cancer develops when cancer cells spread from their point of origin to another organ within the body. This stage of cancer, which is also referred to as metastatic or secondary cancer, is the most advanced form of cancer and is often the most difficult to treat.