Staging is a way of describing or classifying a cancer based on the extent of cancer in the body. The stage is determined by:
- location of the primary tumour
- size of the tumour
- amount of spread to surrounding (local) tissues
- whether or not the cancer has spread to the lymph nodes
- whether or not the cancer has spread to other parts of the body
Cancers from the same site and with similar microscopic characteristics (histology) usually share similar patterns of growth and behaviour.
Doctors may change the stage assigned to a cancer as they learn more about the disease. For example, a CT scanCT scanAn imaging technique that uses a computer to put a series of x-ray images together to create a 3-dimensional picture of organs, tissues, bones and blood vessels inside the body. A contrast medium may be injected to make organs and structures show up clearly on the x-ray images. or MRIMRIAn imaging technique that uses a magnetic field to produce pictures of areas inside the body. A contrast medium may be injected into the body to make structures and organs show up clearly on the image. may show additional disease (metastasis) in a distant organ. If metastasis is discovered, staging will often change. Therefore, complete staging may only be possible after additional testing or surgery.
Staging systems evolve over time as more data is gathered about a particular type of cancer.
Knowing the cancer's stage helps the doctor:
- choose the most effective treatment(s)
- evaluate treatment for a particular stage of cancer
- estimate a person's chance for recovery or prognosisprognosis1. The expected outcome or course of a disease. 2. The chance of recovery or recurrence.
- choose an appropriate clinical trial, if a person would like to participate in one
The 2 basic ways to determine the stage of a cancer are clinical staging and pathological staging. Definite staging is based on all information that is used in both clinical staging and pathological staging to give the most accurate stage of a cancer.
Clinical staging is based on information gathered at the time of diagnosis (before treatment). Clinical staging is specifically based on:
- physical examination
- laboratory test results
- imaging studies
- observations during surgical exploration or other examinations
Clinical staging is used to plan the initial treatment.
Pathological staging is based on the microscopic examination of tissue from the primary tumour, lymph nodes or metastases after it has been removed by surgery. It is used to plan additional (adjuvantadjuvantTreatment given in addition to the first-line therapy (the first or standard treatment) to help reduce the risk of a disease (such as cancer) coming back (recurring).) treatment, estimate prognosis and plan follow-up.
Doctors may change the clinical stage of a cancer based on additional information found during pathological examination.
Different staging or classification systems are used for different cancer sites and types. The Union for International Cancer Control (UICC) and the American Joint Committee on Cancer (AJCC) both use the TNM system to describe the extent of many solid tumour cancers. The UICC and AJCC TNM classifications are similar.
Additional or other staging systems are used for certain types of cancers:
- melanoma – Breslow's classification (thickness or depth) and Clark's classification (level of invasion)
- ovarian, endometrial, cervical, vaginal and vulvar cancers – International Federation of Gynecology and Obstetrics (FIGO)
- Hodgkin and non-Hodgkin lymphoma – Ann Arbor Staging System
- leukemias – staging is not normally used except in chronic lymphocytic leukemia (CLL)
- Rai and Binet classification systems are used for CLL.
- multiple myeloma – Durie-Salmon Staging System and International Staging System
TNM stands for tumour, node, metastasis. The TNM staging system describes the following:
indicates the size of the primary tumour and the degree of spread into nearby tissues (local invasion)
indicates whether or not the cancer has spread to nearby lymph nodes, the size of the nodes that contain cancer and how many lymph nodes contain cancer
indicates whether or not cancer has spread (metastasized) to distant organs
Additional letters or numbers are placed after T, N and M to provide more specific details. Each type of solid tumour cancer (such as breast, colon, lung or prostate cancers) has its own TNM staging classification.
Once doctors determine the TNM description for a particular cancer, they assign it an overall stage from 0 to IV (0–4). These numbers help identify whether the cancer is at an early or advanced stage. The higher the number, the more advanced the cancer. The stages usually follow this pattern:
- stage 0 – carcinoma in situcarcinoma in situA very early stage of cancer in which tumour cells have not yet invaded surrounding tissues.
- stages I and II – the cancer is limited to the organ or location where it began or it may have spread to a nearby structure (localized spread)
- stage III – the cancer has spread further into a surrounding structure or to the regional lymph nodes (regional spread)
- stage IV – the cancer has spread to a distant site in the body (metastatic spread)
Recurrence means that cancer has come back after treatment. Cancer can recur several weeks, months or years after treatment. Cancer may come back in:
- the original site or organ, or very close to it (local recurrence)
- lymph nodes or tissues near the original site (regional recurrence)
- organs or tissues in another part of the body (distant recurrence)
When a new tumour is found in someone who has been treated for cancer, it is usually a recurrence or metastasis from the primary cancer. It is possible to develop a new primary tumour, unrelated to the original cancer, but this is unusual.
The initial stage of cancer does not change as the cancer progresses, nor if it comes back.