Identifying the stage of cancer growth

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Before making decisions about the best way to treat a patient’s cancer, a doctor needs to determine how advanced the cancer growth is and if it has spread elsewhere in the body. This is called cancer staging. Understanding the stage of cancer growth also allows the doctor to give their patient more accurate information on the likely prognosis (what normally happens with this type of cancer) and identify the best course of treatment.1

Staging is always based on the characteristics of the cancer at the time of diagnosis. Although the cancer will continue to change, and doctors will record information about new characteristics, the cancer stage will not change.1

Cancer staging provides doctors information about:1

  • The original site of a cancer’s growth.
  • The type of cell effects. For example, skin cancer may affect basal skin cells or squamous skin cells.
  • The extent of the growth of the tumour.
  • The extent to which the cancer has spread from the original site to the lymph nodes or other organs.
  • What the cancer cells look like and their chances of growing and spreading.

The different staging systems

There are several different systems oncologists use to classify a cancer’s stage, which your doctor may talk to you about. Some systems can be used to stage many different types of cancer, while others have been developed for staging specific types of cancer.1

TNM

TNM is an acronym for Tumour, regional lymph Nodes and distant Metastasis. It is one of the most detailed cancer staging systems. Each of these three features of the cancer are described using a numbering system:1,2

  • Tumour: The size or extent of the tumour is described as TX (not measurable), T0 (not identifiable) or T1-4 (with increasing number indicating increasing tumour size).
  • Nodes: The extent to which the cancer has spread to regional lymph nodes is described as NX (not measurable), N0 (no spread to regional lymph nodes) or N1-3 (with higher numbers indicating spread to a greater number of lymph nodes).
  • Metastasis: Distant metastasis (the extent to which the cancer has spread to different parts of the body) is described as MX (not measurable), M0 (no distant metastasis) or M1 (distant metastasis).

Five Stages (numeric)

This is a classification system which uses information from TNM staging to groups cancers into one of five categories. These stages are:2

  • Stage 0: Indicates the presence of abnormal cells which are not cancerous, but may become cancerous. It corresponds to the classification of cancer in situ (see below).
  • Stage 1: Indicates cancer which is confined to the organ in which the cancerous tumour started growing, and remains reasonably small. It has not spread to the lymph nodes or other organs.
  • Stage 2: Indicates a tumour that is confined to its original organ but has grown too large to be classified as a Stage 1 cancer, or, depending on the type of cancer, a tumour that has spread only to lymph nodes close to the original organ.
  • Stage 3: Typically indicates a larger tumour that has started to spread to the surrounding tissues and lymph nodes, but not to distant areas of the body.
  • Stage 4: Indicates cancer has spread from the original organ to another organ in a distant part of the body. This is also referred to as metastatic cancer.

Five stages (descriptive)

This is a classification system mainly used in cancer registries. Although doctors do not typically use this system in clinical practice, people may hear doctors using the five descriptive stages to describe cancer. They are:1

  • In situ: Indicates abnormal changes in cells which may become cancerous. At this stage a tumour may be referred to as having precancerous changes or non-invasive cancer.
  • Localised: Indicates a cancerous tumour that remains confined to the original organ in which it started to grow.
  • Regional: Indicates cancer has spread from the tumour to nearby (regional) lymph nodes, organs or tissues.
  • Distant: Indicates cancer that has spread to distant lymph nodes, organs or tissues.
  • Unknown: A classification given to cancers for which the stage cannot be determined because there is not enough information about the cancer’s growth and spread.

Identifying cancer biomarkers that influence its growth and treatment

Tests undertaken to diagnose and stage cancer may also identify biomarkers (markers indicating the nature of the biological abnormality of the cancer cells).3 For example, changes to the genes (DNA) of cells, can be indicative of certain types of cancer. 4,5 For example, increased levels of methylated DNA within genes that suppress tumour growth can be a sign of certain cancers, including colorectal cancer.5

There are many additional biomarkers that a doctor may test for after a cancer diagnosis has been made. Testing for these biomarkers can help doctors determine the best treatment for the patient.3 For example, if a woman is diagnosed with breast cancer, the doctor may perform tests to determine whether or not the breast cancer cells contain oestrogen receptors and/or progesterone receptors. This can help guide treatment because the greater the number of oestrogen or progesterone receptors, the more likely the cancer is to respond to hormonal therapy.6

 

References

  1. National Cancer Institute. About cancer: Staging. 2015 (cited 11 December 2016). Available from: [URL link]
  2. Cancer Research UK. Stages of Cancer. 2014 (cited 11 April 2017). Available from: [URL link]
  3. Henry NL, Hayes DF. Cancer biomarkers. Mol Oncol. 2012;6(2):140-6. [Full text]
  4. Sethi S, Shadan A, Philip PA, Sarkar FH. Clinical advances in molecular biomarkers for cancer diagnosis and therapy. Int J Mol Sci. 2013;14(7):14771-84. [Full text]
  5. PhillipsThe role of methylation in gene expression. Nature Edu. 2008; 1(1):116. [Full text]
  6. Badowska-Kozakiewicz AM, Patera J, Sobol M, Przybylski J. The role of oestrogen and progesterone receptors in breast cancer: Immunohistochemical evaluation of oestrogen and progesterone receptor expression in invasive breast cancer in women. Contemp Oncol (Pozn). 2015;19(3):220-5. [Full text]
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