title: Animal-type melanoma: a clinical and histopathological study of 22 cases from a single institution.
abstract: Background Animal-type melanoma is a rare distinct melanoma subtype, characterized by proliferation of heavily pigmented epithelioid and spindled melanocytes that resembles the heavily pigmented melanomas seen in grey horses. While animal-type melanoma is generally considered to be more indolent than conventional melanoma, only a limited number of cases have been reported and, as such, the clinical characteristics of animal-type melanoma are incompletely understood. Objectives To characterize the clinical and histopathological features of animal-type melanoma, and determine any features that may predict outcome. Patients/Methods Data was extracted from a prospectively collected melanoma database (1994-2008), and a retrospective pathology database (1991-2008) for all patients with a diagnosis of both equivocal (8) and unequivocal (14) malignant animal-type melanoma. We reviewed the clinical and histopathological features, including the sentinel lymph node biopsy (SLNB) status. Results A total of 22 patients were identified, with a median age of 35 years. The median Breslow depth was 2.22 mm. A SLNB was performed in 17 patients, eight (47%) were positive. Younger age was associated with: (i) animal-type melanoma with features equivocal for malignancy (median age of 7 vs. 48 years, P = 0.01), and (ii) a negative SLNB (median age 12 vs. 53 years, P = 0.03). Four patients with unequivocal animal-type melanoma developed recurrent metastatic disease, with one patient death. No patient with an equivocal animal-type melanoma or negative SLNB developed recurrent disease; however, this did not reach statistical significance (P = 0.13 and P = 0.09, respectively). Conclusions Animal-type melanoma has a propensity for regional lymphatic metastasis and is rarely capable of disseminated metastatic disease and death. Animal-type melanoma appears to exhibit a spectrum of biological behaviour, with young patient age associated with more indolent disease.
authors.affiliation: Department of Dermatology, University of Michigan Medical School and Comprehensive Cancer Center, Ann Arbor, MI, USA. mathewlu@med.umich.edu
authors.forename: M W
authors.initials: MW
authors.lastname: Ludgate
authors.forename: D R
authors.initials: DR
authors.lastname: Fullen
authors.forename: J
authors.initials: J
authors.lastname: Lee
authors.forename: R
authors.initials: R
authors.lastname: Rees
authors.forename: M S
authors.initials: MS
authors.lastname: Sabel
authors.forename: S L
authors.initials: SL
authors.lastname: Wong
authors.forename: T M
authors.initials: TM
authors.lastname: Johnson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008207:Lymphatic Metastasis / Q000473:pathology; D008297:Male; D008545:Melanoma / Q000401:mortality / Q000473:pathology*; D008875:Middle Aged; D012189:Retrospective Studies; D021701:Sentinel Lymph Node Biopsy; D012878:Skin Neoplasms / Q000401:mortality / Q000473:pathology*; D016019:Survival Analysis; D055815:Young Adult