It is a problem with the melanocytes that causes melanoma. They become damaged – mainly by UV radiation or through a faulty gene passed down through families, and grow out of control. A clump of mutated melanocytes (or any cancer cells) are known as a tumour.

Melanoma occurs mainly due to too much exposure to sunlight or UV radiation but it may also occur in places that have never seen the sun.  This may be due to families passing down faulty genes that make moles develop into melanoma or for melanomas to form where there haven’t been any moles.

The most common places for melanomas to occur are the skin of men’s backs and on women’s legs, but melanoma can occur anywhere on the body. Other common places are:

  • The head and neck
  • the skin under the fingernails
  • the soles of the feet or palms of the hands.

Melanoma can be treated successfully if it is caught early but if it spreads to other parts of the body (known as metastatic melanoma) the prognosis or outcome is poor.  This is why early detection is so important (see our ‘prevention and early detection’ tab)

Staging of melanoma

Melanoma is staged or classified according to how thick it is – or how deep through the layers of skin it has spread.  This includes whether it has spread through the skin layers to the lymph nodes (these drain fluid around your body) or to other organs around the body (known as metastatic melanoma)

Medical staff can use different ways to assess your melanoma:

  • physical examination using a dermatoscope to look at the melanoma closely
  • biopsies – taking small amounts of the mole or suspicious skin for a look under a microscope
  • Xray, CT or MRI scans- to see if the melanoma cells have travelled from the original spot to elsewhere in the body

(see our ‘prevention and early detection’ tab)

Medical staff use the following staging method and this will help them plan your treatment and estimate your prognosis (or outlook):

T  = Tumour

Doctors look at how far the melanoma tumour has grown within the skin. This is worked out looking at the thickness of the melanoma using the Breslow measurement (done by a pathologist using your biopsy).  The thinner the melanoma, the better the prognosis.  In general, melanomas less than 1mm thickness have a very small chance of spreading.

The tumour is given a rating of 0-4.  It may also be given a small letter which doctors use to give information to other doctors on whether the surrounding skin has ulcerated as well and how quickly the tumour cells are dividing.  Ask your doctor if you have any questions about the stage of your melanoma.

N = Nodes (spreading to Lymph nodes)

N stands for spread to nearby lymph nodes (bean-sized collections of immune system cells, to which cancers often spread first). The N category is given 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 may also be assigned a small letter a, b, or c, depending on how it has spread. Ask your doctor if you have any questions about the stage of your melanoma.

M = Metastasized (or spread to distant organs)

This classification is based on whether the melanoma has spread from the area in which is started or originated (known as the primary tumour). It takes into account which organs it has reached, and may also rely on measurements of a substance called LDH in the blood

One the TNM ratings have been done, they are combined to give an overall score or staging (Clark’s level). These are usually given a number I-IV.

In general, patients with lower stage cancers have a better outlook for a cure or long-term survival.

DID YOU KNOW…..Clark's level is a staging system, used in conjunction with Breslow's depth, which describes the level of anatomical invasion of the melanoma in the skin. It was developed by Wallace H. Clark, Jr. at Harvard University and Massachusetts General Hospital in the 1960s.

clark level diagram

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