Melanoma is one of the forms of skin cancer. It develops in melanocytes or pigment cells . For ease, we will use the terms skin cancer and singular melanoma. But there are different kinds, and even in the case of similar diseases, each person has specific peculiarities.
Anatomy of the skin
Our skin is made up of three layers . The superficial layer is called the epidermis , the middle layer is called the dermis, and the lower layer is called subcutaneous connective tissue or hypodermis .
The epidermis consists mainly of two types of cells : basal cells and squamous cells. In addition, pigmentary cells, the melanocytes, are found in the epidermis. The basal cells of the deep layer of the epidermis are able to divide. It is at their level that the new skin cells are formed . Over a period of the order of a month, these new cells migrate upwards and, at the same time, change their shape. Initially, they are round or oval, then they become more angular and later they flatten (squamous cells).
The dermis is made up of connective tissue, also called support tissue. They include sweat glands (which produce sweat), hair follicles associated with sebaceous glands, blood and lymphatic vessels, and nerve endings.
The hypodermis is mainly used for support and consists mainly of fatty tissue.
The functions of our skin
It protects our body, for example against infections and ultraviolet (UV) rays.
It allows us to perceive signals coming from our environment: the cutaneous nerves transmit the painful, sensory and thermal stimuli towards the brain which transforms these stimuli into sensations.
Finally, the skin plays a large role in the regulation of body temperature , the sweat glands of the skin contributing largely to this regulation.
In Belgium, according to figures from the Cancer Registry, in 2013, 2,635 new cases of skin cancer were registered. Despite the prevention campaigns, this cancer is clearly increasing .
Before puberty, melanoma is very rare . Subsequently, it can occur at any age, but is proportionally more common before age 60 compared to most other cancers.
Types of melanomas
Melanoma literally means black tumor . This type of skin cancer appears in melanocytes or pigment cells. Normal melanocytes are present in disseminated form throughout the skin. They can also be gathered in small clusters and then form pigmented spots, such as moles (naevi).
We talk about melanoma when, at a place on the skin, the pigment cells turn into cancer cells . The resulting malignant tumor will appear as a pigmented spot that grows or grows, changes color, and so on.
Where are the melanomas?
A melanoma can appear at the level of an existing mole or an isolated pigment cell in a “healthy” skin zone, with no pre-existing pigment spots. Melanomas can develop anywhere in the skin . In women, they appear a little more frequently in the legs, in men at the trunk. Areas covered with hair, such as the scalp, can also be affected.
Exceptionally , a melanoma can appear in the lining of an organ. A mucous membrane is a thin layer of tissue that lines the cavities of the body. These melanomas can affect the mouth, nasal cavities and throat, as well as the vagina and anus. Melanoma sometimes occurs also in the lining of the eyelids and in the eye itself.
Metastases of skin cancer
Like any other cancer, skin cancer can send metastases elsewhere in the body. Through the lymphatic system, the tumor cells reach the lymph nodes of the neck, armpits or groin (depending on the location of the tumor) and multiply to give rise to lymph node metastases.
The cancer cells can also spread through the bloodstream to other parts of the body , for example to the lungs, liver, other skin site or the brain. Nevertheless, the metastases of a melanoma almost always begin by invading the regional lymph nodes, before reaching other distant organs by blood.