Staging describes or classifies a cancer based on how much cancer is in the body and where it is when first diagnosed. This is often called the extent of cancer.
The stage often includes the size of the tumour, which parts of the organ have cancer, whether the cancer has spread (metastasized) and where it has spread.
Why are cancers staged?
Doctors use stage as a common way to describe the size and spread of cancers. The stage of cancer is used to:
- help plan treatment
- predict a person’s outlook, the course of the disease or the chance of recovery (called a prognosis)
- predict how well the treatment will work
- find people for research studies in clinical trials
- help you choose a clinical trial if you want to join one
Cancers in the same part of the body (such as colon cancer) with the same stage tend to have a similar prognosis and are usually treated the same.
How are cancers staged?
Doctors use exams and tests to stage a cancer. The exams and tests show where the cancer is and approximately how much cancer is in the body. To stage a cancer, doctors may do a physical exam, blood tests, imaging tests or a biopsy. They may also look at the tissue with cancer during surgery or after the tissue is removed by surgery.
Different staging systems are used for different types of cancer. The most common staging system used in Canada is the TNM system. TNM stands for tumour, node (lymph node) and metastasis. It is used to stage most solid tumour cancers. Solid tumour cancers, like breast or prostate cancer, form lumps. Other staging systems are used to stage some types of solid cancers and cancers of the blood and immune system, such as some types of leukemia and lymphomas.
TNM staging system
T stands for tumour. It describes the size of the main (primary) tumour. It also describes if the tumour has grown into other parts of the organ with cancer or tissues around the organ. T is usually given as a number from 1 to 4. A higher number means that the tumour is larger. It may also mean that the tumour has grown deeper into the organ or into nearby tissues.
N stands for lymph nodes. It describes whether cancer has spread to lymph nodes around the organ. N0 means the cancer hasn’t spread to any nearby lymph nodes. N1, N2 or N3 means cancer has spread to lymph nodes. N1 to N3 can also describe the number of lymph nodes that contain cancer as well as their size and location.
M stands for metastasis. It describes whether the cancer has spread to other parts of the body through the blood or lymphatic system. M0 means that cancer has not spread to other parts of the body. M1 means that it has spread to other parts of the body.
Sometimes the lowercase letter a, b or c is used to subdivide the tumour, lymph nodes or metastasis categories to make them more specific (for example, T1a). Lowercase “is” is added after T (Tis) to describe a carcinoma in situ.
Types of TNM staging
Solid tumour cancers may be given both a clinical and pathologic stage.
Clinical stage is given before treatment. It is based on the results of exams and tests, such as imaging tests, done when the cancer is found (at the time of diagnosis). Doctors often choose a treatment based on the clinical stage. The clinical stage is shown by a lowercase “c” before the letters TNM on some medical reports.
Pathologic stage is based on the results of tests and exams done when the cancer is found and what is learned about the cancer during surgery and when looking at the tissue after it is removed by surgery. It gives more information about the cancer than the clinical stage. The pathologic stage is shown by a lowercase “p” before the letters TNM on a pathology report.
The clinical and pathologic stages of a cancer can be different. For example, during surgery the doctor may find cancer in an area that didn’t show up on an imaging test so the pathologic stage may result in a higher stage.
Other staging systems
Other staging systems are used for certain types of cancer:
- Ovarian, endometrial, cervical, vaginal and vulvar cancers are often staged using the International Federation of Gynecology and Obstetrics (FIGO) staging system. The FIGO system is based on the TNM system.
- Non-Hodgkin lymphoma uses the Ann Arbor Staging System.
- Hodgkin lymphoma uses the Cotswold staging system.
- Chronic lymphocytic leukemia (CLL) uses the Rai and Binet staging systems.
- Multiple myeloma uses the International and the Durie-Salmon staging systems.
Doctors use the TNM description to assign an overall stage from 0 to 4 for many types of cancer. Stages 1 to 4 are usually given as the Roman numerals I, II, III and IV. Generally, the higher the number, the more the cancer has spread. Sometimes stages are subdivided using the letters A, B and C. For most types of cancer, the stages mean the following:
- stage 0 – carcinoma in situ, a precancerous change
- stage 1 – the tumour is usually small and hasn’t grown outside of the organ it started in
- stages 2 and 3 – the tumour is larger or has grown outside of the organ it started in to nearby tissue
- stage 4 – the cancer has spread through the blood or lymphatic system to a distant site in the body (metastatic spread)
Other ways to describe the stage
When describing the stage, doctors may use the words local, localized, regional, locally advanced, distant or advanced. Local and localized mean that the cancer is only in the organ where it started and has not spread to other parts of the body. Regional and locally advanced mean close to or around the organ. Distant and advanced mean in a part of the body farther from the organ.
Factors that affect the stage
The TNM description includes information about the size of the tumour, what tissues in an organ have cancer, whether the cancer has spread and where it has spread. Other factors that are used to determine the stage for some types of cancer include:
- cancer cell type (such as adenocarcinoma or squamous cell carcinoma)
- tumour marker levels (such as PSA in men with prostate cancer)
- genetic information about the cancer (such as which genes are mutated)
The stage of cancer doesn’t change
Once a person is told what stage the cancer is (either the clinical or pathologic stage), the stage of cancer doesn’t change. If a stage 2 cancer comes back (recurs) after it is treated, it is still stage 2 cancer that has recurred. And if the cancer has spread to a distant part of the body after it is treated, it is still stage 2 cancer but it is metastatic. This is important because the stage at diagnosis is used to study survival statistics and treatments for specific stages of cancer.
Restaging helps doctors plan further treatment when cancer comes back or gets worse after the initial treatment. Restaging doesn’t mean that a stage 2 cancer changes to a stage 3 cancer. The stage of a cancer doesn’t change. But a tumour initially staged as a T2 may be described as a T3 or T4 if the cancer has grown larger or grown into nearby tissues. This may be found with further tests after treatment. When restaging is done, it is shown with a lowercase “r” before the letters TNM on a medical report.