What Is Cancer Staging?
Knowing the stage, or extent, of cancer helps a doctor plan treatment and predict the chance of recovery.
When cancer is diagnosed, one of the key pieces of information a doctor needs is the stage of the cancer. Staging is a process to find out how severe the cancer is. This is done by discovering how far the cancer has spread from its original location.
Staging is important because it:
- Helps a doctor plan treatment
- Can be used to predict the chance of recovery (prognosis)
- Can help identify studies of new treatments (clinical trials) the person might qualify for
To determine the stage of a cancer, doctors may use results from many sources, such as:
- Physical exams, which can help the doctor locate the tumor
- Imaging tests such as x-rays, ultrasounds, CAT scans, MRIs or PET scans
- Lab tests, such as tests of blood, urine and other fluids
- Pathology reports based on taking tissue samples (biopsies) and examining them under a microscope
- Surgical reports, which can provide specific information on the tumor and lymph nodes after surgery
The stage is then designated using the staging systems below.
The stage is a shorthand way to describe whether and where cancer has spread. Doctors often use the following systems to convey this information.
TNM staging is the most commonly used system. It has three elements: T for tumor, N for node and M for metastasis. Within each of these categories, numbers are used to denote the size or extent of the tumor and how much the cancer has spread. A larger number means a larger or more extensive tumor.
T describes the tumor itself.
- TX: Primary tumor cannot be evaluated
- T0: No evidence of primary tumor
- Tis: Carcinoma in situ (early cancer that has not spread to neighboring tissue)
- T1, T2, T3, T4: Size and/or extent of the primary tumor
N describes the involvement of lymph nodes around the tumor.
- NX: Regional lymph nodes cannot be evaluated
- N0: No regional lymph node involvement (no cancer found in the lymph nodes)
- N1, N2, N3: Involvement of regional lymph nodes (number and/or extent of spread)
M describes metastasis, or whether the cancer has spread to other parts of the body.
- MX: Distant metastasis cannot be evaluated
- M0: No distant metastasis (cancer has not spread to other parts of the body)
- M1: Distant metastasis (cancer has spread to distant parts of the body)
The TNM system is used for most types of cancer. But the letters and numbers may not mean the same thing for different types of cancer. The TNM system is not used for some types of cancer, such as cancers of the blood and brain.
Roman numeral staging
The TNM information is often combined into an overall stage that uses Roman numerals. Most cancers have four stages (I-IV). Some also have a stage 0. The smaller the number, the easier the cancer is to treat and the better the prognosis.
- Stage 0: Early cancer that has not spread to neighboring tissue (carcinoma in situ)
- Stage I: Cancer that is small, has not invaded deeply into nearby tissues and has not spread to lymph nodes or other tissues
- Stage II: Cancer that has spread into surrounding tissues but not beyond the area where it started
- Stage III: Cancer that has spread to nearby lymph nodes
Stage IV: Cancer that has metastasized (spread) to other parts of the body