Primary chondroid melanoma.
BACKGROUND
Malignant melanoma is notorious for the wide range of histologic patterns it can assume, among the least frequent of which is chondroid melamona.


METHODS
Two cases of primary chondroid melanoma of the distal lower extremity were studied. Tissue for light microscopy was fixed in formalin, embedded in paraffin, and processed routinely. In one case, transmission electron microscopy and immunohistochemical evaluation were performed.


RESULTS
Both cases exhibited melanoma in-situ, a conventional (non-chondroid) invasive component, and areas of chondroid differentiation, as confirmed by strongly positive staining with Alcian blue at pH 2.5 and Safranin O. Immunohistochemically, one case expressed S-100 protein and vimentin, and did not express gp100 (HMB-45), tyrosinase, MART-1, the Mel-5 antigen, the NKI/C3 antigen, CD45Ro, cytokeratin, or desmin. Electron microscopy of the chondroid component revealed occasional tumor cells with rare, membrane-bound, electron-dense organelles; the extracellular compartment showed amorphous ground substance consistent with cartilaginous differentiation.


CONCLUSIONS
Chondroid change in the absence of osteogenic differentiation is extremely rare in malignant melanoma. Melanoma should be considered in the differential diagnosis of primary cutaneous neoplasms exhibiting cartilaginous differentiation.
Ackley
C D
CD
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Prieto
V G
VG
Bentley
R C
RC
Horenstein
M G
MG
Seigler
H F
HF
Shea
C R
CR
D000368:Aged; D001706:Biopsy; D001859:Bone Neoplasms / Q000473:pathology*; D002278:Carcinoma in Situ / Q000473:pathology; D002454:Cell Differentiation; D002813:Chondrosarcoma / Q000473:pathology*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008545:Melanoma / Q000473:pathology*; D008875:Middle Aged; D012878:Skin Neoplasms / Q000473:pathology*