What is melanoma?
Melanoma is the deadliest form of skin cancer, while other non-melanoma skin cancers (NMSC) are less aggressive. Skin cancer, including both NMSC and melanoma, is the most common cancer in Canada; it will account for nearly the same number of diagnoses as the four major cancers (lung, breast, colorectal and prostate) combined—with an estimated 6, 800 new cases of melanoma in 2015, with 1,150 dying from it [1]. The five-year net survival rate for melanoma for is 88%, as its symptoms tend to present earlier on [2].
Between 2001 and 2010, the incidence of melanoma has increased significantly among men and women, rising 2.3% per year in men and 2.9% in women. The mortality rate from melanoma has also increased although not as strongly as the incidence rate [3].
As the body’s largest organ, the skin protects it from injury, infection and ultraviolet light from the sun. However, intense, occasional UV radiation can cause damage to skin cells. This UV exposure is the primary cause of melanoma.
The skin is composed of two main layers: the epidermis (top layer) and the dermis (bottom layer). Melanoma occurs in the melanocytes on the epidermis. Melanocytes are cells that produce melanin, a pigment that gives human skin, hair and eyes their color. When melanocytes develop abnormally, they can cause precancerous conditions. For example, an atypical mole, or dysplastic nevus, is likelier to become cancerous [5].
Types of melanoma
The four basic types of cutaneous melanomas are melanomas of the skin, and are the most common types of melanoma. They fall into four categories, three of them begin in situ — meaning they occupy only the top layers of the skin — and sometimes become invasive; the fourth is invasive from the start. Invasive melanomas are more serious, as they penetrate deeper into the skin and may spread to other areas of the body.
The Four Basic Types Melanomas fall into four basic categories. Three of them begin in situ — meaning they occupy only the top layers of the skin — and sometimes become invasive; the fourth is invasive from the start. Invasive melanomas are more serious, as they have penetrated deeper into the skin and may have spread to other areas of the body.
- Superficial spreading melanoma is the most common type, accounting for about 70 percent of all cases. This type is most often seen in young people. The melanoma grows along the top layer of the skin for a fairly long time before penetrating more deeply. The first sign is the appearance of a flat or slightly raised discolored patch that has irregular borders and is somewhat asymmetrical in form. The color varies, and there may be visible areas of tan, brown, black, red, blue or white. This type of melanoma can occur in a previously benign mole and can be found almost anywhere on the body, but is most likely to be found on the torso in men, the legs in women, and the upper back in both.
- Lentigo maligna melanoma is similar to the superficial spreading type, as it remains close to the skin surface for quite a while, and usually appears as a flat or mildly elevated mottled tan, brown or dark brown discoloration. They develop from very slow growing pigmented areas of skin called lentigo maligna or Hutchinson’s melanotic freckle. This type of in situ melanoma is found most often in the elderly, arising most commonly on chronic sun-exposed skin, damaged skin on the face, ears, arms and upper torso.
- Acral lentiginous melanoma is a rare melanoma which spreads superficially before penetrating more deeply. It is different from the others, as it usually appears as a black or brown discoloration under the nails or on the soles of the feet or palms of the hands. This type of melanoma can often advance more quickly than superficial spreading melanoma and lentigo maligna. It is the most common melanoma in dark-skinned persons, and the least common among whites. Acral Lentiginous Melanoma (ALM) accounts for 50% of all melanomas in Asians and people with dark skin but is only 5% of all diagnosed melanoma in the US.
- Nodular melanoma is usually invasive at the time it is first diagnosed. It begins to grow downwards, deeper into the skin, quite quickly if it is not removed. There is often a raised area on the skin surface with this type of melanoma. Nodular melanomas are usually dark brownish black or black, but can occasionally be blue, gray, white, brown, tan, red or skin tone. It is found most often in middle-aged people and in parts of the body only exposed to the sun occasionally—so most often on the chest or back. They can also come up in areas of skin that have not received a great deal of sun. And they may not necessarily develop from a mole which was already there. This is the most aggressive of the melanomas, and is found in 10 to 15 percent of cases.
Rare forms of melanoma
Melanoma can occur anywhere in the body, including in the internal organs. Melanoma of the skin is also called cutaneous malignant melanoma. Cutaneous is another word for the skin.
While most melanomas diagnosed in dark-skinned persons are far less common than those diagnosed in whites, there are rarer types, along with ALM, which have higher rates of diagnosis:
- Subungual melanoma has a higher proportion of melanomas (15% to 35%) in dark-skinned groups but only 3% of cases of melanoma in whites
- Plantar melanoma is rare in white people, accounting for only 2% to 8% of melanoma cases. However, it arises on the plantar surface of the foot in 35% to 90% of patients diagnosed with melanoma of African-American, Asian, or Hispanic descent.
- Mucosal melanoma is a melanoma which can occur in any mucous membrane of the body, including the nasal passages, the throat, the vagina, the anus, or in the mouth.
- Ocular melanoma is a rare form of melanoma which occurs in the eye.
[6][7] Information taken from the Skin Cancer Foundation and Cancer Research UK
[1] Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics 2015. Toronto, ON: Canadian Cancer Society; 2015.
[2] Canadian Cancer Statistics Advisory Committee. Canadian Cancer Statistics 2018. Toronto, ON: Canadian Cancer Society; 2018.
[3] Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics 2015. Toronto, ON: Canadian Cancer Society; 2015.
[4] Canadian Cancer Society. The Skin. Digital image. What Is Melanoma? Canadian Cancer Society, 2014. Web. 12 May 2015.
[5] “What Is Melanoma?” Melanoma Research Foundation. Melanoma Research Foundation, 2015. Web. 15 June 2015.
[6]”Skin Cancer Foundation.” Types of Melanoma. Skin Cancer Foundation, 2015. Web. 15 June 2015.
[7] “Types of Melanoma.” Cancer Research UK. Cancer Research UK, 17 Jan. 2014. Web. 03 July 2015.
