At the time of diagnosis, staging of the cancer is done to help determine the prognosis (the likely future course and outcome of the cancer) and type of treatment a patient should receive. Doctors classify the cancer according to a staging system that describes the size of the tumour and the extent of cancer spread.

In order to collect some of the information needed to stage a cancer, doctors may do a more extensive physical examination and order a set of tests including blood tests, bone scans, MRI (magnetic resonance imaging), CAT scans (computer-assisted axial tomography), and ultrasounds.

Many cancer types are staged using the TNM system:

  • T (tumour): describes the size and extent of the tumour
  • N (nodes): describes whether the cancer has spread to the lymph nodes
  • M (metastasis): describes whether the cancer has spread to distant parts of the body

The TNM system also assigns a number to each letter:

  • T: ranges from T0 (no tumour) to T4 (large/extensive tumour)
  • N: ranges from N0 (cancer has not spread to lymph nodes) to N3 (cancer has spread extensively to lymph nodes)
  • M: ranges from M0 (cancer has not spread to distant parts of the body) to M1 (cancer has spread)

So the overall score for a particular cancer will have 3 letters and 3 numbers: for example, T1N2M0.

The exact staging system and prognosis for each stage differs, depending on the type of cancer.

The TNM scores for a cancer can be linked to different stages (exactly how they're linked depends on the type of cancer):

  • Stage 0: Early cancer that is still found only in the layer of cells where it started (also called carcinoma in situ).
  • Stages 1-3: Cancer that has not yet spread to another organ (as you move from stage 1 to stage 3, the cancers become larger and more extensive).
  • Stage 4: Cancer that has spread to another organ (metastasized).

If you have been diagnosed with cancer, check with your doctor to find out the type and stage of your cancer. This will help you find more information on your treatment and prognosis.