Melanoma staging explained

Patient guide

After a diagnosis of melanoma, your medical team will work out the ‘stage’ of your melanoma. The stage is a way of describing the key features of your melanoma and is helpful in guiding the best treatment and follow-up for you.  Your stage provides an indication of how advanced your melanoma is. Generally, the higher the stage, the more advanced it is.

UNDERSTANDING MELANOMA STAGING

How is the stage worked out?

The melanoma staging system has been developed by the American Joint Committee on Cancer (AJCC) – the most up-to-date version is the 8th edition.
Three pieces of information are combined to provide the stage or TNM staging:

  • Tumour (T),
  • Node (N)
  • Metastasis (M)

Some of the important information needed to determine the stage of your melanoma will not be known after your initial biopsy and it may take a little time to determine your stage. Your stage will be re-assessed every time more information about your melanoma becomes available. The ‘pathological stage’ is determined by what is seen when your melanoma is examined under a microscope by a pathologist. The ‘clinical stage’ is based on what your medical team find when they examine you or what is seen if you have any scans.

TUMOUR (T)

Breslow thickness

The thickness or depth of the melanoma is calculated by a pathologist looking at your melanoma under a microscope and is measured from the surface of your skin to the deepest point of the melanoma. It is measured in millimetres (mm). In general, melanomas less than 1mm in thickness have a very small chance of spreading.

  • Tumour Size: This describes the size of the primary (original) melanoma and whether it has invaded nearby tissue.
  • Tis – melanoma in situ or stage 0 melanoma (this is on the surface of the skin and is not malignant)
  • T1 – ≤1.0 mm
  • T2 – , >1.0–2.0 mm
  • T3 – >2.0–4.0 mm
  • T4 – >4.0 mm

It is important to realise that a T4 or pT4 melanoma is NOT a Stage 4 melanoma – a pT4 melanoma is a way of describing a melanoma that is more than 4 mm thick

Your pathologist will also examine whether your melanoma is ulcerated. Melanomas that are ulcerated are indicated by the little letter ‘b’ (e.g T2b) and have a slightly higher risk of coming back than melanomas that are not ulcerated, which are given the little letter ‘a’ (e.g.T2a).

 

NODE (N)

Lymph Node involvement

This describes whether lymph nodes near the primary melanoma also contain melanoma.

The lymph nodes may contain enough melanoma to be found when your medical team examine you or might be seen on a scan. Alternatively the lymph nodes may contain microscopic deposits of melanoma that are only found when a pathologist looks at your lymph node under a microscope. The N stage will also be used to describe whether there has been any spread of the melanoma to skin near the primary melanoma. Separate deposits of melanoma are occasionally found close to the original melanoma site. These are referred to as In-transit metastases if they are further than 2cm from the primary tumour, or satellite metastases if they are closer than 2cm.

  • N0 – no lymph node involvement
  • N1 – 1 involved lymph node or in-transit, satellite, and/or microsatellite metastases
  • N2 – 2 or 3 involved nodes or in-transit, satellite, and/or microsatellite metastases with one involved node
  • N3 – 4 or more involved nodes or in-transit, satellite, and/or microsatellite metastases with two or more involved nodes, or any number of lymph nodes that have stuck together without or with in-transit satellite, and/or microsatellite metastases

Your pathologist will also take into account whether the lymph node that was involved with melanoma was obvious to your medical team, or whether it was an unexpected finding only seen using a microscope. Your ‘N’ stage will be assigned a letter a, b or c which takes into account whether the melanoma was obvious to your medical team in the clinic, and whether melanoma was found only in a lymph node or had also formed micro-satellite or in transit deposits. The more melanoma that is found in a lymph node or in nearby skin, the greater the chance of further problems arising in the future.

 

METASTASIS (M)

Metastasis:

This describes the spread of the melanoma elsewhere in the body.
M0 – there is no evidence that the melanoma has spread to another part of the body
M1 – there is evidence, either from clinical examination or on imaging, that the melanoma has spread to another part of the body

The table below summarizes how Tumour Size, the Number of Lymph Nodes Involved, and Metastasis (or spread) of melanoma contribute toward its stage.

Adapted from:
Melanoma Staging: American Joint Committee on Cancer (AJCC) 8th Edition and Beyond. Gershenwald JE, Scolyer RA Annals of Surgical Oncology 2018, 2105-2110
https://link.springer.com/article/10.1245/s10434-018-6513-7

Relevant References:

JE, Scolyer RA et al., Melanoma Staging: American Joint Committee on Cancer (AJCC) 8th Edition and Beyond. Annals of Surgical Oncology 2018, 2105-2110 https://link.springer.com/article/10.1245/s10434-018-6513-7