What is melanoma ?
Un mélanome est un cancer qui prend naissance dans les cellules de la peau appelées mélanocytes.
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The skin is the largest organ in the body . Its surface area is about 2 m², and its weight is estimated at 3.5 kg.
The skin performs many functions :
- It protects the body from heat, cold, sunlight, injuries, and infections ;
- It controls body temperature ;
- It prevents the loss of fluids and substances like sodium or potassium ;
- It removes waste from the body through sweat glands ;
- It provides the sense of touch, allowing the recognition of temperature, pain, and pressure ;
- It helps in the production of vitamin D
The skin is composed of several layers. The two main ones are the epidermis and the dermis. These rest on a third layer, the hypodermis.
Epidermis
The epidermis is the upper or outer layer that gives skin its color. It is made of several different types of cells :
- Squamous cells: They form the outer part of the epidermis and originate from keratinocytes, cells that contain a tough and protective protein called keratin. As keratinocytes move up to the skin's surface, they undergo changes. They become larger and flatter and stick to each other (squamous cells) before dying. Dead squamous cells on the skin's surface constantly shed and are replaced by new cells.
- Melanocytes: These cells are located in the deepest part of the epidermis. They produce melanin, a substance that gives skin its color and helps protect the body from the harmful effects of the sun. When the skin is exposed to the sun's ultraviolet (UV) rays, melanocytes produce more melanin, making the skin darker or tanned. The excess melanin is transferred to other skin cells to protect them from harmful UV rays. The amount of melanin produced also depends on individuals' genetic makeup. People with fair or pale skin produce less melanin and are more vulnerable to the sun's harmful effects.
- Other specialized cells are present in the epidermis. Langerhans cells present foreign substances to other cells of the immune system to defend against them. Merkel cells are thought to contribute to the sensation of touch.
Dermis
The dermis is the thickest layer of skin located beneath the epidermis. Collagen and elastin are proteins in the dermis that give the skin its strength, stretchability, and flexibility. The dermis consists of many structures, including :
- Blood vessels that carry blood cells, nutrients, and oxygen to the skin ;
- Lymphatic vessels that carry immune system cells and help fight infections ;
- Hair follicles where hair originates ;
- Sweat glands that produce sweat to control body temperature ;
- Sebaceous glands that produce oils to keep the skin and hair smooth ;
- Nerve endings that help provide the sense of touch.
Hypodermis
The hypodermis is mainly made up of fatty tissue. It helps retain body heat and protect internal organs. (Source: Canadian Cancer Society).
Melanocytes can cluster together and form moles (nevi) on the skin. They appear as spots that are usually brown or pink. Most people have a few moles. These are non-cancerous (benign) tumors.
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The evolution of moles ( nevi ) is most often benign. The likelihood of a mole (nevus) turning into melanoma is very low, probably less than 1 in 100,000 (source: arcagy.org). They can thus be left as they are.
However, caution should be exercised when moles are located in areas that are traumatized or subject to repeated friction, such as the belt area, feet, hands, or cheeks (razor). Caution is also advised when there are many nevi, when a nevus is large (atypical nevus), or if it is present from birth (congenital nevus).
Sometimes, changes affecting melanocytes can lead to precancerous conditions or melanoma. To identify these changes, it is useful to perform a self-examination and follow the ABCDE rule.
Expert perspective
To help detect a precancerous condition or melanoma early, it is recommended that everyone apply the ABCDE rule :
A. for A symmetrie : Half of the nevus is not symmetrical with the other half.
B. for B order irregularity : The borders can be notched and poorly defined.
C. for C olor variation : The color varies from one area of the lesion to another.
D. for D iameter : Often larger than 6 mm, the size of a pencil eraser.
E. for E volution : The appearance of the lesion in terms of shape, color, or especially size has changed.(Source : dermato-info.fr)
If a mole or pigmented skin lesion has all the ABCDE characteristics, it is necessary to consult a dermatologist. This lesion is not necessarily melanoma. However, all primary melanomas have the ABCDE criteria.
Precancerous conditions
Among precancerous conditions, there are atypical nevi (dysplastic nevi) and Dubreuilh's melanosis.
Expert perspective
An atypical nevus is a nevus that resembles melanoma and meets several criteria of the ABCDE rule.
It is atypical due to its blurry or irregular B orders, uneven C olor, D iameter, and E volution over time.
The two most distinguishing criteria are C olor and E volution over time. They can degenerate into melanoma, particularly in families with cases of melanoma.
Dubreuilh's melanosis is considered a particular superficial melanoma due to its slow progression. It occurs in elderly people and is most often found on the face, less commonly on the hands and feet. It begins as a brown or dark spot that becomes increasingly black, then mottled, after years of evolution.
On this plaque, a black or reddish tumor can develop, ulcerated and affecting the deeper layers. Its treatment is mainly surgical. Other complementary treatments are sometimes necessary. (Source: arcagy.org)
Melanoma
Melanoma most often develops on normal skin and much more rarely from a nevus that degenerates. When cancer cells remain in the epidermis and have not yet invaded the surrounding tissue, the melanoma is termed in situ and still lacks metastatic potential.
In one-quarter of cases, melanomas are invasive from the outset. These melanomas will progress in two phases :
- In the so-called horizontal growth phase, the melanoma progresses horizontally, like an oil stain. During this phase, the melanoma is already invasive as it has crossed the epidermis/dermis junction and can therefore disseminate. This phase lasts several months or even several years, up to seven years.
- If untreated, melanoma can begin its so-called vertical growth phase of deep invasion. This phase is characterized by a protruding nodule that may ooze or bleed. This vertical phase is initially minimally invasive, micro-invasive but carries a high risk of metastasis.
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The formation of metastases is the real problem posed by cancer.
Without metastasis, it would suffice to treat the primary tumor with a local treatment , such as surgery or radiotherapy , to cure most cancers.
The presence of metastases results from the dissemination of cancer cells away from the primary tumor and requires the use of treatments that also disseminate throughout the body (systemic treatments), such as chemotherapy, targeted therapies, hormone therapies, or immunotherapies .
This dissemination of cancer cells to form metastases is a complex phenomenon since cancer cells must leave the primary tumor, use lymphatic vessels and/or blood vessels to circulate in the body, then leave these vessels and penetrate a new organ to multiply within it and form metastases.
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Article updated on Nov 19, 2024
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