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Animal-type melanoma

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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]

Signs and Symptoms

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Animal-type melanoma can develop anywhere on the body, similar to general malignant 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

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Animal-type melanoma has the same likelihood of causes as general malignant 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

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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

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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

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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]

Treatment

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Animal-type melanoma is generally excised, taking note of the clinical margin reliant on Breslow thickness. This is used as a prognostic factor in melanoma and provides a description of how deeply tumor cells have invaded.[20]

Staging

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Melanoma staging is the process of finding out if the melanoma has spread and if so, how far. This assists professionals in determining the intensity of the cancer and allows them to develop the best approach for treatment.[21] Most melanoma specialists coincide with the American Joint Committee on Cancer (AJCC) for cutaneous melanoma staging guidelines:[3]

Cutaneous Melanoma Staging Guidlines
Stage Characteristics
Stage 0 In situ melanoma
Stage 1 Thin melanoma < 2mm in thickness
Stage 2 Thick melanoma > 2mm in thickness
Stage 3 Melanoma spread to involve local lymph nodes
Stage 4 Distance metastases have been detected

References

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  1. ^ Vyas, Ritva; Keller, Jesse J.; Honda, Kord; Cooper, Kevin D.; Gerstenblith, Meg R. (2015-12-01). "A systematic review and meta-analysis of animal-type melanoma". Journal of the American Academy of Dermatology. 73 (6): 1031–1039. doi:10.1016/j.jaad.2015.08.016. ISSN 0190-9622.
  2. ^ "Melanoma Treatment – for health professionals". National Cancer Institute. 26 June 2015. Archived from the original on 4 July 2015. Retrieved 30 June 2015.
  3. ^ a b c d e f g h i "Animal-type melanoma | DermNet". dermnetnz.org. Retrieved 2023-03-19.
  4. ^ Petrescu I, Condrea C, Alexandru A, et al. (2010). "Diagnosis and treatment protocols of cutaneous melanoma: latest approach 2010". Chirurgia (Bucur). 105 (5): 637–43. PMID 21141087.
  5. ^ Avilés-Izquierdo, J. A.; Leis-Dosil, V. M.; Lázaro-Ochaita, P. (2014-03-01). "Animal-type Melanoma: Clinical and Dermoscopic Features of 3 Cases". Actas Dermo-Sifiliográficas (English Edition). 105 (2): 186–190. doi:10.1016/j.adengl.2012.06.034. ISSN 1578-2190.
  6. ^ Schwartzman, Robert Mayer; Orkin, Milton (1962). A Comparative Study of Diseases of Dog and Man. Springfield, IL: Thomas. p. 85. The term 'melanoma' in human medicine indicates a malignant growth; the prefix 'malignant' is redundant.
  7. ^ "Melanoma Risk factors". Mayo Clinic. Archived from the original on 10 April 2017. Retrieved 10 April 2017.
  8. ^ Greene MH (December 1999). "The genetics of hereditary melanoma and nevi. 1998 update". Cancer. 86 (11 Suppl): 2464–77. doi:10.1002/(SICI)1097-0142(19991201)86:11+<2464::AID-CNCR3>3.0.CO;2-F. PMID 10630172. S2CID 32817426.
  9. ^ Goydos JS, Shoen SL (2016). "Acral Lentiginous Melanoma". Cancer Treatment and Research. 167: 321–9. doi:10.1007/978-3-319-22539-5_14. ISBN 978-3-319-22538-8. PMID 26601870.
  10. ^ "Melanoma Risk factors". Mayo Clinic. Archived from the original on 10 April 2017. Retrieved 10 April 2017.
  11. ^ Rünger TM, Farahvash B, Hatvani Z, Rees A (January 2012). "Comparison of DNA damage responses following equimutagenic doses of UVA and UVB: a less effective cell cycle arrest with UVA may render UVA-induced pyrimidine dimers more mutagenic than UVB-induced ones". Photochemical & Photobiological Sciences. 11 (1): 207–15. doi:10.1039/c1pp05232b. PMID 22005748. S2CID 25209863.
  12. ^ Wang SQ, Setlow R, Berwick M, Polsky D, Marghoob AA, Kopf AW, Bart RS (May 2001). "Ultraviolet A and melanoma: a review". Journal of the American Academy of Dermatology. 44 (5): 837–46. doi:10.1067/mjd.2001.114594. PMID 11312434. S2CID 7655216.
  13. ^ Oliveria SA, Saraiya M, Geller AC, Heneghan MK, Jorgensen C (February 2006). "Sun exposure and risk of melanoma". Archives of Disease in Childhood. 91 (2): 131–8. doi:10.1136/adc.2005.086918. PMC 2082713. PMID 16326797.
  14. ^ "WHO | The World Health Organization recommends that no person under 18 should use a sunbed". WHO. Archived from the original on 16 June 2009.
  15. ^ "Melanoma Risk factors". Mayo Clinic. Archived from the original on 10 April 2017. Retrieved 10 April 2017.
  16. ^ Khlat M, Vail A, Parkin M, Green A (May 1992). "Mortality from melanoma in migrants to Australia: variation by age at arrival and duration of stay". American Journal of Epidemiology. 135 (10): 1103–13. doi:10.1093/oxfordjournals.aje.a116210. PMID 1632422.
  17. ^ a b "Familial Malignant Melanoma". Cancer.Net. 2012-06-25. Retrieved 2023-03-19.
  18. ^ Li, Suli; Chu, Yihang; Wang, Ying; Wang, Yantong; Hu, Shipeng; Wu, Xiangye; Qi, Xinwei (2022-10-14). "Distinguish the Value of the Benign Nevus and Melanomas Using Machine Learning: A Meta-Analysis and Systematic Review". Mediators of Inflammation: 1–8. doi:10.1155/2022/1734327.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  19. ^ "Excision of skin lesions | DermNet". dermnetnz.org. Retrieved 2023-03-19.
  20. ^ Breslow, Alexander (1970). "Thickness, Cross-Sectional Areas and Depth of Invasion in the Prognosis of Cutaneous Melanoma". Annals of Surgery. 172 (5): 902–8. doi:10.1097/00000658-197011000-00017. PMC 1397358. PMID 5477666.
  21. ^ "Stages of Melanoma Skin Cancer". www.cancer.org. Retrieved 2023-03-19.
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