What is a melanoma?1

Melanoma is a type of malignant skin cancer. It starts in skin cells called melanocytes. These cells produce melanin, the pigment that causes the skin to become brown or tan, which spreads over the entire skin. Due to this, most (but not all) melanomas appear as brown spots on your skin with irregular shapes and different sizes.

Some facts about melanoma:

  • Melanoma is the 2nd most common type of cancer.
  • As many as 1 Belgian in 50 will be affected by melanoma before the age of 75.
  • Melanoma is less common than other skin cancers, but is much more dangerous.
  • Melanoma can appear on any part of the skin.
  • Melanoma can quickly spread to other parts of the body if not detected at an early stage.

Causes and development of melanoma2

Melanomas can develop anywhere in the skin. Sometimes melanomas arise in a birthmark that has been there a long time, but sometimes it develops without a birthmark being present first. It is not really clear why someone gets a melanoma.

How does a melanoma develop?

Normal, healthy skin cells are constantly growing, dividing and maturing, eventually dying and being shed from the skin. However, sometimes the DNA of the cells is damaged. This damage can lead to abnormal growth or survival of the cells. Since a cell copies its own DNA before dividing to make new cells, any mutations in the original cell are passed on to the cells that follow.3

A melanoma develops from melanocytes that inherit or undergo a mutation. As a result, they grow and divide faster than normal. Research has shown that certain genes are more involved than others in every type of cancer, for melanoma, mutations are mainly found in the BRAF, NRAS, KIT, PTEN, GNAQ and GNA11 genes that mutate4.

In melanoma, the melanocytes also begin to spread to the surrounding surface layers of the skin. If that metastasis is not stopped, the melanoma will grow and spread along the epidermis (the outermost layer of skin cells). That’s how it penetrates into the deeper skin layers and comes into contact with the lymph nodes and blood vessels. In this way, melanoma spreads to other parts of the body.3

Are there any known risk factors of melanoma?

There are some risk factors that make it more likely that someone will develop a melanoma:

  • Family history of melanoma;
  • Having often been sunburned at a young age;
  • Having used a lot of sunbeds;
  • Having pale skin that burns quickly with red or light blonde hair;
  • Having more than 5 “clinically atypical” birthmarks;
  • Having more than 100 birthmarks on the body;
  • Having a congenital birthmark (congenital nevus) measuring 20 cm or larger; having previously had a melanoma.


What are the stages of malignant melanoma?5

A cancer stage is a term used to describe its size, depth and potential spread.

To speak of a certain stage of melanoma, the focus is first on the thickness of the tumour (Breslow thickness) and ulceration (ulcer formation). Together with the size, number of glands involved and location of possible metastases, these determine the stage of the disease.

In melanoma, we speak of 5 stages.

Stage 0 Melanoma

The cells are present only in the top layer of skin (the epidermis) and have not spread to the dermis (the thick layer of skin tissue under the epidermis). Melanoma stage 0 is also called melanoma or tumour “in situ”. Since the melanoma is only in the top layer of skin, people with melanoma in situ are usually not at risk of the melanoma spreading to other parts of the body.

Stage 1 Melanoma

A melanoma stage 1 is no thicker than 2 mm and have spread only in the skin.

Stage 2 Melanoma

A melanoma stage 2 is between 2–4 mm thick and have not yet spread to the lymph nodes or anywhere else in the body.

Stage 3 Melanoma

A melanoma stage 3 has spread to the lymphatic vessels or lymph nodes closest to the melanoma, but not anywhere else in the body.

Stage 4 Melanoma

A melanoma stage 4 has spread to further areas of the skin or further lymph nodes. Or they have spread to other organs such as the lungs, liver or brain. This is called advanced or metastatic melanoma.


More information about melanoma

More information about melanoma and genetic mutations in melanoma can be found in the brochures below.


Melanoom brochure for patients and family (Dutch)

Order | Download




BRAF mutation brochure for patients and family (Dutch)

Order | Download


Melanoom brochure for patients and family (French)

Order | Download


BRAF mutation brochure for patients and family (French)

Order | Download



  1. Rapport 2021 Le cancer de la peau en Belgique – Fondation contre le cancer
  2. – Dernière consultation : 12/12/2022
  3. Aim at Melanoma Foundation. How melanoma develops. Disponible à l’adresse : Dernière consultation : février 2020.
  4. Bello DM, et al. Cancer Control. 2013;20(4):261-281
  5. Gerschenwald et al. CA Cancer J Clin 2017;67:472-492

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