“Staging” is the process used to determine the size of a melanoma and where and how far it has spread. Staging helps your healthcare team plan:
- The kind of treatment you need
- The likely risk of the melanoma coming back after treatment
- Whether you need tests to see if the melanoma has spread into lymph nodes close to the melanoma (sentinel lymph node biopsy).
Melanoma, the most aggressive form of skin cancer, is always staged.
You will often hear your doctors talk about the Breslow thickness of your melanoma. Essentially, the Breslow thickness is defined as the total vertical height (thickness) of the melanoma. It is measured from the very top (called the “granular layer”) to the area of deepest penetration in to the skin. The pathologist will look at the melanoma under the microscope after it has been removed and use an instrument called an “ocular micrometer” is used to measure the thickness. In general, the higher the Breslow thickness, the worse the prognosis (keep in mind that these survival rates are averages and may not reflect your individual case). Due to its accuracy in predicting outcomes, the Breslow thickness has been incorporated into the standard TNM staging system for melanoma.
The TNM system.
Several tests and procedures are used to assign T, N, and M categories and a grouped stage. The TNM system for staging contains 3 key pieces of information:
T stands for tumour (how far it has grown within the skin and other factors). The T category is assigned a number (from 0 to 4) based on the tumour’s Breslow thickness (how far down it has grown). It is also assigned a small letter “a” if it is not ulcerated or a “b” if it is ulcerated. Ulceration means the layer of skin covering the melanoma is absent. This is seen under a microscope after a biopsy.
- Tis – melanoma cells are only in the very top layer of the skin surface
- T1 – the melanoma is less than 1 milllimetre thick
- T2 – the melanoma is between 1 mm and 2 mm thick
- T3 – the melanoma is between 2 mm and 4 mm thick
- T4 – the melanoma is over 4 mm thick
N stands for spread to nearby lymph nodes (small bean-shaped collections of immune system cells that help the body fight infections and cancers). The N category is assigned a number (from 0 to 3) based on whether the melanoma cells have spread to lymph nodes or are found in the lymphatic channels connecting the lymph nodes. It is also assigned a small letter: “a” if melanoma cells can only be seen with the microscope or “b” if they can be seen with the naked eye. A letter “c” is assigned if there are very small deposits of melanoma in the nearby skin or if the melanoma is in skin lymphatic channels around the tumour – these are called ‘in transit metastases’ or ‘satellites’.
- N0 – there are no melanoma cells in the nearby lymph nodes
- N1 – there are melanoma cells in one lymph node
- N2 – there are melanoma cells in 2 or 3 lymph nodes
- N3 – there are melanoma cells in 4 or more lymph nodes
The M category is based on whether the melanoma has metastasised (spread) to distant organs, which organs it has reached, and sometimes on blood levels of a substance called LDH.
- M1a – melanoma cells have spread to skin in other parts of the body or to lymph nodes far away from the where the melanoma started growing
- M1b – melanoma cells have spread to the lung
- M1c – melanoma cells have spread to other organs or cause high blood levels of LDH
AJCC staging system
There is an in-depth staging system for all scenarios of melanoma. However, for a quick reference it can be simplified into:
Stages I & II: Melanoma found only at the point it started. This is called ‘local’ or ‘localised’ disease because the tumour is confined to the site of the original primary.
Stage III: Melanoma has spread to the lymph nodes or along the skin towards the lymph nodes (satellites or in transit metastases). This is called ‘regional’ disease because the tumour has spread via the lymphatic system to the draining lymph nodes in the vicinity of the primary tumour. If the patient presents with in transit or satellite metastases then this is called ‘loco-regional’ disease.
Stage IV: Melanoma has spread to other distant parts of the body such as lungs, liver, brain and distant skin. This is called ‘distant’ disease because the tumour has spread via the bloodstream to other parts of the body not directly connected with the primary tumour.
The AJCC staging system is used by all cancer professionals when discussing or planning the treatment of melanoma. Please click here to download a summary sheet of the AJCC staging system for melanoma (Version 8).
If you are unsure of your stage, please ask your specialist nurse or doctor.