Animal-type melanoma
From Wikipedia, the free encyclopedia
Animal-type melanoma is a rare subtype of melanoma that is characterized by heavily pigmented dermal epithelioid and spindled melanocytes.[1][2] Animal-type melanoma is also known to be called equine-type melanoma, pigment synthesizing melanoma, and pigmented epithelioid melanocytoma (PEM).[3] While melanoma is known as the most aggressive skin cancer,[4] the mortality for PEM is lower than in other melanoma types.[5] Animal-type melanoma earned its name due to the resemblance of melanocytic tumors in grey horses.[3]
All ages, including childhood, are susceptible to animal-type melanoma. According to recent studies, it is unknown which age group it is most prominent in and males and females are equally as likely to be impacted.[3]
Animal-type melanoma can develop anywhere on the body, similar to general melanoma.[6] It will be observed as arising from normal, unaffected skin, rather than skin with a pre-existing mole. Animal-type melanoma appears as a dark brown/black papule and resembles a melanocytic tumor in grey horses.[3]
Early signs of animal-type melanoma can be summarized by the ABCDE criteria, excluding the E.
- Asymmetry
- Border irregularity
- Color variation
- Diameter more than 6mm
Cause
Animal-type melanoma has the same likelihood of causes as general melanoma. Fair skin, family history, and sun damage are all common and well-known risk factors. Melanomas are usually caused by DNA damage resulting from exposure to UV light from the sun. Genetics also play a role[7][8] and is responsible for melanoma occurring in skin areas with little sun exposure (i.e. mouth, feet soles, palms, and genital areas).[9]
A weakened immune system aids in cancer development due to a lack of ability to fight cancer cells. Having more than 50 moles is also an indication of an increased risk of melanoma.[10]
UV radiation
UVA and UVB rays are wavelengths expressed by the sun and absorbed by skin cell DNA that results in DNA damage.[11] Exposure to radiation (UVA and UVB) is one of the major contributors to the development of melanoma.[12] Likewise, occasional extreme sun exposure (sunburn) is related to melanoma.[13] The use of sunbeds that contain deeply penetrating UVA rays has also been linked to the development of melanoma.[14]
Having multiple severe sunburns increases the likelihood that future sunburns develop into melanoma. This is due to cumulative damage.[15]
Genetics
When determining risk for melanoma, the intensity and duration of sun exposure, the age at which sun exposure occurs, and the degree of skin pigmentation all play a role.[16] Familial melanoma is known as melanoma passed from generation to generation within a family. Two genes, CDKN2A and CDK4, have been linked to familial melanoma. When a mutation occurs in either of these genes, it will result in an increased risk of melanoma. While these two are primarily linked, the alterations in these genes only account for a small percentage of familial melanoma.[17]
Familial melanoma follows an autosomal dominance inheritance pattern where a mutation happens in only one copy of the gene. This means a parent gene may either pass along a copy of their normal gene or a copy of the gene with the mutation.[17]
Diagnosis
By the time animal-type melanoma has been diagnosed, it likely has been a year or longer since it was first present on the skin. After a clinical assessment acknowledges a lesion on the skin that may point to melanoma, a dermascopic analysis may be required.[18] When under analysis, animal-type melanoma appears to have a structureless blue pattern, irregular whitish structures, and irregular, large blood vessels.[3]
If determined to be melanoma, the lesion may be removed with an excision biopsy (completely cutting out and removing a skin lesion).[19][3] A histology report that determines animal-type melanoma may include:
- Heavily pigmented melanocytic tumor
- Epithelioid and splindled melanocytes
- Bland or malignant cytological appearance
- Low mitotic activity
- Infrequent ulceration
- No features to suggest regression[3]
Due to the unknown nature of animal-type melanoma, a pathologist may find it challenging to make a definite diagnose between animal-type melanoma and blue naevi due to the similarities between the two.[3]