Melanoma, Cutaneous

Melanoma, Cutaneous


image



Basic Information image



Definition


Neoplasm of dermal melanocytes or “nevus cells” within the basal layer of the epidermis



Synonym(s)




• Equine melanocytic disease


• Cutaneous melanoma



Epidemiology



Species, Age, Sex




• Occurs mostly in aging, gray and white horses, and mules.


• Bays, chestnut, and other colors are less frequently affected.


• More than 80% of gray horses older than 15 years develop melanoma.


• Some have suggested that all gray horses will develop melanoma over their lifetime.


• Case reports in non-gray horses, usually of the hoof, coronary band, and metacarpal/metatarsal area.


• The juvenile form may occur in horses of any coat color.


• Sex predisposition reported by some but not consistently.



Genetics and Breed Predisposition




• Most common in Lipizzaners, Arabians, and Quarter Horses.


• Arabians are thought to be predisposed because they progressively change color with age; they are usually white by 9 years of age.



Risk Factors




• The gray phenotype appears to be a disturbance in melanin metabolism, which stimulates the formation of melanoblasts or increased activity, resulting in overproduction of melanin in the dermis.


• Autosomal dominant trait associated with high incidence of melanoma and vitiligo-like depigmentation (cis-acting regulatory mutation)



Geography and Seasonality


Generally accepted to be more common in sunnier latitudes



Clinical Presentation



Disease Forms/Subtypes


Four distinct clinical syndromes:



• Melanocytic nevus


image Average age of presentation is 5 years (range, 2 months to 16 years)

image Approximately 50% of all melanotic tumors in horses

image Considered benign

image Gray and non-gray horses

image Discrete, small, superficial tumors that involve the superficial dermal layer with variable pigmentation and occasional mitotic figures noted on histopathology

image Studies suggest an Arabian overrepresentation and a female predisposition

• Dermal melanoma


image Average age of presentation is 13 years (range, 2–19 years)

image Discrete masses that occur in mature, middle-aged gray horses at various locations (see Physical Exam)

image Located in the deep dermis and characterized by small, homogenous, indistinct, round tumor cells with condensed chromatin and dense cytoplasmic pigmentation

image More aggressive forms appear to occur in atypical locations (limbs) and at a younger age

• Dermal melanomatosis


image Average age of presentation is 17 years (range, 7–29 years); multiple sites or coalescence

image Older gray horses, frequently in typical locations (tail base, perineum, and genitalia)

image Histologically similar to dermal melanoma but more confluent

image High metastatic rate

image Surgical excision usually not feasible

• Anaplastic melanoma


image Average age of presentation is 20 years and not exclusively in gray horses

image May occur more commonly in other colors (chestnut)

image Extremely pleomorphic, epithelioid cells with poor pigmentation, widespread single-cell invasion of the dermis and numerous mitotic figures noted on histopathology


History, Chief Complaint




• Usually related to size and location of tumor burden


• Physical obstruction of the anal sphincter, penis, prepuce, or vulvar commissure may occur, which may result in dyschezia, dysuria, and difficulty with coitus and parturition.


• Metastatic melanoma: May present for weight loss, colic, epistaxis, ataxia, and respiratory distress


• 43% have peripheral edema from lymphatic obstruction


• Clinical progression: Three forms:


image Slow growth over a number of years without metastasis
< div class='tao-gold-member'>

Related posts:

  1. Aggressive Stallion Behavior
  2. Aflatoxin Toxicosis
  3. Biliary Atresia
  4. Black Widow Spider Toxicosis

Stay updated, free articles. Join our Telegram channel
Tags:
Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Melanoma, Cutaneous

Full access? Get Clinical Tree
Get Clinical Tree app for offline access