Cancer staging describes the size of a cancer and how far it has spread in the body. In the UK, staging is used to guide treatment decisions, estimate outlook (prognosis), and ensure consistent communication between healthcare professionals.
Most solid cancers in the UK are staged using the internationally recognised TNM staging system, overseen globally by the Union for International Cancer Control (UICC) and adopted in UK practice through bodies such as the Royal College of Pathologists and NHS cancer services.
The TNM System Explained
TNM stands for:
T (Tumour): The size of the primary tumour and how far it has grown into surrounding tissue.
N (Nodes): Whether cancer has spread to nearby lymph nodes.
M (Metastasis): Whether the cancer has spread to other parts of the body.
These categories are combined to determine an overall stage, usually numbered from Stage 0 to Stage 4.
What the Stages Mean
Stage 0
Also known as carcinoma in situ. Abnormal cells are present but have not spread beyond their original location.
Stage 1
The cancer is small and contained within the organ where it started. It has not spread to lymph nodes or distant sites.
Stage 2 and Stage 3
The cancer is larger and/or has spread to nearby lymph nodes or surrounding tissues, but not to distant parts of the body. These stages are often divided into subgroups (such as 2A, 2B, 3A, etc.), depending on tumour size and lymph node involvement.
Stage 4
The cancer has spread to distant organs, such as the liver, lungs, brain or bones. This is also known as metastatic or advanced cancer.
Clinical and Pathological Staging
In UK practice, doctors may refer to:
Clinical staging (cTNM): Based on scans, biopsies and physical examination before treatment.
Pathological staging (pTNM): Determined after surgery, when the tumour and lymph nodes can be examined under a microscope.
These may differ, and pathological staging is often more precise.
Important Differences Between Cancers
Not all cancers are staged in the same way. For example:
Blood cancers such as leukaemia are not staged using TNM.
Lymphomas use staging systems such as the Ann Arbor system.
Some cancers increasingly include molecular and genetic markers alongside TNM staging to guide targeted treatments.
Why Staging Matters
Understanding the stage of a cancer helps:
Plan the most appropriate treatment
Estimate likely outcomes
Determine eligibility for clinical trials
Provide patients with clear information about their diagnosis
Staging systems continue to evolve as research advances and treatments improve.
