title: Malignant melanoma with a myxoid stroma: a diagnostic pitfall on fine-needle aspiration biopsy.
abstract: Malignant melanoma (MM), both primary and metastatic, may be associated with a prominent myxoid stromal reaction causing diagnostic confusion on fine-needle aspiration biopsy (FNAB), most often with sarcomas that demonstrate a myxoid stroma, particularly malignant peripheral nerve sheath tumor (MPNST). We present a case of a 32-yr-old man with no past medical history who presented with a unilateral neck mass clinically suspicious for lymphoma. FNAB produced a specimen composed of large sheets of anaplastic cells encased in a myxoid stroma that was S100 and vimentin-positive but HMB-45-negative. A diagnosis of MPNST was made. Excision demonstrated a metastatic MM of unknown primary, with a prominent myxoid stromal reaction. A repeat HMB-45 was again negative. Electron microscopy demonstrated intracytoplasmic melanasomes and cisternae of rough endoplasmic reticulum with intracisternal parallel tubules, confirming the diagnosis. Although HMB-45 is typically negative in both tumors, S100 should be strongly positive in myxoid MM and only focal in MPNST.
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
authors.forename: D
authors.initials: D
authors.lastname: Elliott
authors.forename: M B
authors.initials: MB
authors.lastname: Pitman
mesh_terms: D000328:Adult; D001707:Biopsy, Needle; D003937:Diagnosis, Differential; D006258:Head and Neck Neoplasms / Q000737:chemistry / Q000473:pathology* / Q000601:surgery; D006801:Humans; D007150:Immunohistochemistry; D018208:Liposarcoma, Myxoid / Q000473:pathology; D008223:Lymphoma / Q000473:pathology; D008297:Male; D008545:Melanoma / Q000737:chemistry / Q000473:pathology* / Q000601:surgery; D020460:Melanosomes / Q000648:ultrastructure; D018317:Nerve Sheath Neoplasms / Q000473:pathology; D010524:Peripheral Nervous System Neoplasms / Q000473:pathology; D009418:S100 Proteins / Q000032:analysis; D014746:Vimentin / Q000032:analysis
chemical_list: D009418:S100 Proteins; D014746:Vimentin