title: Cutaneous amelanotic signet-ring cell malignant melanoma with interspersed myofibroblastic differentiation in a young cat.
abstract: The diagnosis of malignant melanoma can be difficult because these tumors can be amelanotic and may contain diverse variants and divergent differentiations, of which the signet-ring cell subtype is very rare and has only been described in humans, dogs, cats, and a hamster. We describe herein histopathologic and immunohistochemical approaches taken to diagnose a case of signet-ring cell malignant melanoma with myofibroblastic differentiation in a cat. A tumor within the abdominal skin of a 2-year-old cat was composed of signet-ring cells and irregularly interwoven streams of spindle cells. Both neoplastic cell types were periodic-acid-Schiff, Fontana, and Sudan black B negative. Signet-ring cells strongly expressed vimentin and S100 protein. Spindle cells strongly expressed vimentin and smooth muscle actin; some cells expressed S100, moderately neuron-specific enolase, and others variably actin and desmin. A few round cells expressed melan A, and a few plump spindle cells expressed melan A and PNL2, confirming the diagnosis of amelanotic signet-ring cell malignant melanoma with myofibroblastic differentiation in a cat. Differential diagnoses were excluded, including signet-ring cell forms of adenocarcinomas, lymphomas, liposarcomas, leiomyosarcomas, squamous cell carcinomas, basal cell carcinomas, and adnexal tumors.
authors.affiliation: Institut für Veterinär-Pathologie, Justus-Liebig-Universität Giessen, Giessen, Germany manuela.hirz@vetmed.uni-giessen.de.
authors.forename: Manuela
authors.initials: M
authors.lastname: Hirz
authors.affiliation: Institut für Veterinär-Pathologie, Justus-Liebig-Universität Giessen, Giessen, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Herden
mesh_terms: D000005:Abdomen / Q000473:pathology; D000818:Animals; D002371:Cat Diseases / Q000175:diagnosis* / Q000473:pathology; D002415:Cats; D002454:Cell Differentiation; D003937:Diagnosis, Differential; D005260:Female; D008545:Melanoma / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*; D009210:Myofibrils / Q000473:pathology; D012878:Skin Neoplasms / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*; D000096142:Cutaneous Malignant Melanoma
keywords: Amelanotic signet-ring cell malignant melanoma; immunohistochemistry; myofibroblastic differentiation; skin; young cats