What Is Cancer Staging?
When cancer is diagnosed, the doctor will want to determine the stage, or extent, of the disease. Knowing a patient's stage helps the surgeon or oncologist (cancer specialist) make recommendations about the best course of treatment. Doctors will consider the chances of being cured by surgery alone, type of surgery that is likely to give the best possible outcome, and whether additional treatments (radiation, hormone, or chemotherapy) will be helpful. At the same time, the doctor will consider other factors, such as a patient's general health and treatment preference.
To determine the stage of a cancer, doctors use results from the physical exam, diagnostic tests including X-rays, ultrasound, biopsies, computerized tomography scans, magnetic resonance imaging, positron emission tomography, blood tests and other tests combined to create a picture of where the cancer is located, how large a tumor is (if a tumor is present), whether the cancer has spread, and what subtype of cancer it is.
Cancer staging applies to almost all cancers except for most forms of leukemia. Since leukemias involve the entire body, not a localized area like other cancers, staging doesn't make as much sense. A few forms of leukemia do have staging systems, though, which reflect how advanced the disease is. (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
Each type of cancer is staged according to specific characteristics. "In situ" cancers are cancers that have been diagnosed at the earliest possible stage. (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
There are two related cancer-staging systems: an overall stage grouping that uses Roman numerals, and the TNM system created by the American Joint Committee on Cancer. (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
Roman numeral staging
Stage I or "local" cancers have been diagnosed early and have not spread
Stage II cancer has spread into surrounding tissues, but not beyond the location of origin
Stage III or "regional" cancer has spread to nearby lymph nodes
Stage IV or "distant" cancers have metastasized - spread - to other parts of the body and are the most difficult to treat
The TNM staging system (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
The TNM Staging System is based on characteristics of the Tumor, Lymph Nodes, and Metastasis. Each of these is categorized separately and classified with a number to give the total stage. Basically, the larger the number, the greater the cancer involvement. (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
T classifies the extent of the primary tumor, and is normally given as T0 through T4, with T0 representing a tumor that hasn't even started to invade the local tissues (in situ), to T4 representing a large primary tumor that has probably invaded other organs. (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
N: Lymph Nodes
N classifies regional lymph node involvement. Regional lymph nodes are those draining the area around the primary tumor. (Involvement of distant lymph nodes means the cancer has metastasized, or spread.) N0 means no lymph node involvement, while N4 means extensive involvement. (Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)
M is either M0 if there are no metastases, or M1 if there are metastases.
(Cancer Staging, Ajcc Atlas Cancer Staging, Ajcc Cancer Manual Staging)