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Understanding Melanoma Part 2

Posted by Dr James Burt on 2 February 2017

Now we have described the structure of your skin and how the normal skin pigment system works we can start discussing what happens when a melanoma develops.

You will remember the melanocytes ( pigment cells) sit at the bottom of the epidermis layer of your skin.

These cells are present when you are born and present when you die and do not normally divide or reproduce themselves during your lifetime.

Melanocytes are spaced out at regular intervals along the bottom of your epidermis.

The very first sign of a melanoma is a clump of melanocytes all clustered together within the epidermis. This may not look very impressive but it is very significant when you consider these cells are normally seen as single cells separated by some distance. What this appearance indicates is that one or more of these cells is dividing. This should not be happening if these cells are following the DNA instructions inside the cell. It tells that the DNA within one or more of these cells has been damaged and these cells are no longer being controlled by the normal control mechanisms.

In the majority of cases we believe the environmental factor responsible for damaging the DNA  within the melanocytes is UV radiation ( SUNLIGHT).

So this earliest sign of a melanoma is known by several names which can be confusing.

These names are level 1 melanoma, melaloma in situ, lentigo maligna melanoma or Hutchinson's melanotic freckle.

All these conditions describe the same situation where abnormal melanocytes are identified forming clusters but the abnormal cells are only seen within the epidermis. No abnormal cells are seen in the dermis.

If the abnormal melanocytes break through or invade into the dermis the disease has progressed and is now known as an invasive melanoma.

Invasive melanomas are usually classified using 2 classification systems.

These are the Breslow thickness and the Clarke level.

The Breslow thickness is simply determined by the pathologist looking down the microscope and identifying the deepest melanocyte that can be seen and then measuring back up to the top of the epidermis. The Breslow thickness is usually reported in fractions of a millimeter ( 0.6mm, 2,1 mm etc). This is the single most important factor we look at  when advising on treatment of melanoma.

The Clarke level is a documentation by the pathologist where melanocytes have invaded in relation to the structure of the skin.

  • Clarke Level 1 - abnormal melanocytes confined to the epidermis only
  • Clarke Level 2 - melanocytes seen in the papillary dermis ( upper dermis)
  • Clarke Level 3 - melanocytes seen at the junction of the papillary dermis ( upper dermis) with the reticular dermis ( deep dermis)
  • Clarke Level 4 - melanocytes seen in the reticular dermis ( deep dermis)
  • Clarke Level 5 - melanocytes extend beyond the dermis ( beyond the full thickness of the skin) into deeper tissue ( often the underlying fat layer , but can be muscle or other tissues depending on the site of the tumor)

There are several other factors which will be reported when a pathologist makes the diagnosis of melanoma. These are important but the most important factor  guiding treatment recommendation will be the Breslow thickness and to a lesser degree the Clarke level.

I will discuss the other secondary factors in the next article.
Dr James BurtAuthor:Dr James Burt
About: Dr Jamie Burt was born and educated in Melbourne, attending the University of Melbourne and graduating with MBBS in 1998. He is a member of the Senior Medical Staff at St. Vincent’s Hospital, Melbourne, and was Head of Reconstructive and Plastic Surgery at the Peter MacCallum Cancer Institute until 2004. Known for his respectful, informative, and caring approach, Jamie has been caring for patients for over 15 years.
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