While there are many forms of cancer, they tend to share common characteristics that allow them to be categorised into stages. The stages of cancer are a means of classifying the size of a cancer and how far it has progressed into surrounding tissues and other parts of the body.

Why is Staging Important?

The stage of cancer enables an oncologist to formulate an effective treatment plan, which might include surgery, chemotherapy or radiation therapy. Doctors may use information from test results done before surgery (clinical stage) or from the results of what is found during surgery (pathological stage) to determine the overall stage.

Staging Systems

There are two main types of cancer staging systems, the TNM system and the number system, however, some blood and lymph cancers have different staging systems.

The TNM System

TNM is an acronym for Tumour, Node and Metastasis. This system describes the size of the primary Tumour, whether the cancer has spread to the lymph nodes and whether it has metastasised, or spread to other parts of the body.

  • T indicates the size of a cancer, classified as 1, 2, 3 or 4, from small to large.
  • N determines whether cancer has spread to the lymph nodes, categorised between 0 and 3, from none to many lymph nodes containing cancer cells.
  • M refers to whether the cancer has spread to others part of the body, categorised as either 0 or 1, where 1 indicates that the cancer has spread.
Classification Examples:
  • A small cancer that has spread to the lymph nodes but not elsewhere in the body: T2 N1 M0.
  • Advanced cancer that has spread to other parts of the body: T4 N3 M1.

The Number System

Doctors typically combine the TNM results with other pertinent information to determine a cancer stage ranging from 0 – IV, often denoted in Roman numerals.

  • Start 0: Called carcinoma in situ, indicates abnormal cells with the potential to become cancer.
  • Stage I: Called early-stage cancer, indicates a cancer that is relatively small and contained within one area.
  • Stage II: Indicates that the cancer is larger than in stage I, but has not spread into the surrounding tissues, but may have spread into lymph nodes nearby.
  • Stage III: Indicates that the cancer is more extensive than in stage II and has spread into surrounding tissues and lymph nodes.
  • Stage IV: Called advanced or metastatic cancer which has spread to other parts of the body.

Please note that this article is a brief description of the various stages of cancer, and is intended for the layperson to gain an overview of the subject. There is a great deal of information which is not within the scope of this introductory article.