title: Melanoma associated with a dermatofibroma.
abstract: BACKGROUND
  Dermatofibromas are common benign cutaneous fibrohistiocytic neoplasms, whereas melanomas are potentially aggressive malignancies. Differentiating these two entities can occasionally be difficult.
  
  
  METHODS
  We report the case of a 56-year-old female presenting with a firm pink papule on the left thigh.
  
  
  RESULTS
  Histopathology revealed atypical melanocytes in the epidermis and papillary dermis with numerous mitotic figures and intraepidermal pagetoid spread. Within the dermis was a poorly demarcated collection of epithelioid and spindled cells with intermixed keloidal collagen. The atypical melanocytes stained for MART-1 and S-100, whereas the underlying fibrohistiocytic tumor took up factor XIIIa immunostain, confirming the diagnosis of invasive malignant melanoma occurring in association with a dermatofibroma.
  
  
  CONCLUSIONS
  This case emphasizes the role of immunohistochemical stains in correctly diagnosing melanocytic and histiocytic neoplasms.
authors: Vanderbilt University Medical Center, Division of Dermatology, Nashville, TN 37232-5227, USA.
authors: Bradley T
authors: BT
authors: Kovach
authors: Alan S
authors: AS
authors: Boyd
mesh_terms: D003937:Diagnosis, Differential; D005260:Female; D018219:Histiocytoma, Benign Fibrous / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D008545:Melanoma / Q000378:metabolism / Q000473:pathology*; D008875:Middle Aged; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology*