What cancer staging is:

Staging is a way of describing the size of a cancer and how far it has grown. When doctors first diagnose a cancer, they carry out tests to check how big the cancer is and whether it has spread into surrounding tissues. They also check to see whether it has spread to another part of the body. 
Cancer staging systems may sometimes include grading of the cancer, which describes how similar a cancer cell is to a normal cell.

Why staging is important

Staging is important because it helps your treatment team to know which treatments you need. If a cancer is just in one place, then a local treatment such as surgery or radiotherapy could be enough to get rid of it completely. A local treatment treats only one area of the body.

If a cancer has spread, then local treatment alone will not be enough. You will need a treatment that circulates throughout the whole body. These are called systemic treatments. Chemotherapy, hormone therapy and biological therapies are systemic treatments because they circulate in the bloodstream.

Sometimes doctors aren't sure if a cancer has spread to another part of the body or not. They look at the lymph nodes near to the cancer. If there are cancer cells in these nodes, it is a sign that the cancer has begun to spread. Cancer doctors call this having positive lymph nodes. The cells have broken away from the original cancer and got trapped in the lymph nodes. But it is not always possible to tell if they have gone anywhere else.

If cancer cells are found in the lymph nodes, doctors usually suggest adjuvant treatment. This means treatment alongside the treatment for the main primary tumour (chemotherapy after surgery, for example). The aim is to kill any cancer cells that have broken away from the primary tumour.

If a cancer has spread, then local treatment alone will not be enough. You will need a treatment that circulates throughout the whole body. These are called systemic treatments. Chemotherapy, hormone therapy and biological therapies are systemic treatments because they circulate in the bloodstream.

Sometimes doctors aren't sure if a cancer has spread to another part of the body or not. They look at the lymph nodes near to the cancer. If there are cancer cells in these nodes, it is a sign that the cancer has begun to spread. Cancer doctors call this having positive lymph nodes. The cells have broken away from the original cancer and got trapped in the lymph nodes. But it is not always possible to tell if they have gone anywhere else.

If cancer cells are found in the lymph nodes, doctors usually suggest adjuvant treatment. This means treatment alongside the treatment for the main primary tumour (chemotherapy after surgery, for example). The aim is to kill any cancer cells that have broken away from the primary tumour.

Types of staging systems

There are two main types of staging systems for cancer. These are the TNM system and the number system.  
The systems mean that 

  • Doctors have a common language to describe the size and spread of cancers
  • Treatment results can be accurately compared between research studies
  • Guidelines for treatment can be standardised between different treatment hospitals and clinics

Some blood cancers or lymph system cancers have their own staging systems.

The TNM staging system

TNM stands for Tumour, Node, Metastasis. This system describes the size of the initial cancer (the primary tumour), whether the cancer has spread to the lymph nodes, and whether it has spread to a different part of the body (metastasised). The system uses numbers to describe the cancer.

T refers to the size of the cancer and how far it has spread into nearby tissue – it can be 1, 2, 3 or 4, with 1 being small and 4 large
refers to whether the cancer has spread to the lymph nodes – it can be between 0 (no lymph nodes containing cancer cells) and 3 (lots of lymph nodes containing cancer cells)
M refers to whether the cancer has spread to another part of the body – it can either be 0 (the cancer hasn't spread) or 1 (the cancer has spread)
So for example, a small cancer that has spread to the lymph nodes but not to anywhere else in the body may be T2 N1 M0. Or a more advanced cancer that has spread may be T4 N3 M1.

Sometimes the letters a, b or c are used to further divide the categories. For example, stage M1a lung cancer (the cancer has spread to the other lung) and stage M1b lung cancer (the cancer has spread to other parts of the body).

The letter p is sometimes used before the letters TNM
– for example, pT4. This stands for pathological stage. It means that the stage is based on examining cancer cells in the lab after surgery to remove a cancer.

The letter c is sometimes used before the letters TNM
– for example, cT2. This stands for clinical stage. It means the stage is based on what the doctor knows about the cancer before surgery. The stage is based on clinical information from examining you and looking at your test results.

Number Staging Systems

Number staging systems usually use the TNM system to divide cancers into stages. Most types of cancer have 4 stages, numbered from 1 to 4. Often doctors write the stage down in Roman numerals. So you may see stage 4 written down as stage IV.

Here is a brief summary of what the stages mean for most types of cancer.

Stage 1 usually means that a cancer is relatively small and contained within the organ it started in.
Stage 2 usually means the cancer has not started to spread into surrounding tissue but the tumour is larger than in stage 1. Sometimes stage 2 means that cancer cells have spread into lymph nodes close to the tumour. This depends on the particular type of cancer.
Stage 3 usually means the cancer is larger. It may have started to spread into surrounding tissues and there are cancer cells in the lymph nodes in the area.
Stage 4 means the cancer has spread from where it started to another body organ. This is also called secondary or metastatic cancer.

Sometimes doctors use the letters A, B or C to further divide the number categories – for example, stage 3B cervical cancer.