DESMOPLASTIC MALIGNANT-MELANOMA OF THE ORAL-MUCOSA - AN UNDERRECOGNIZED DIAGNOSTIC PITFALL

BACKGROUND. Although cutaneous desmoplastic malignant melanoma (DMM) h as been well characterized, those arising from the oral mucosa have be en less well defined. METHODS. We evaluated the clinical and pathologi c features of three patients with biopsy-proven DMM examined at the No rth Carolina Baptist Hospital. Routine hematoxylin and eosin-stained s lides were reviewed in all three cases. Sections from all cases were e xamined immunohistochemically using the avidin-biotin-peroxidase (ABC) technique and employing commercially available antibodies to the foll owing antigens: S-100 protein, HMB-45, NK1C3, and cytokeratin (AE1/AE3 ). Appropriate positive and negative controls were utilized throughout these procedures. Clinical data were obtained from the patients' medi cal records. RESULTS. Age at diagnosis for the three male patients wer e 42, 64, and 75 years. Anatomically, these neoplasms arose from the l eft maxillary oral mucosa (two patients) and the vermilion border of t he lower lip (one patient). Initial incisional biopsies of all three p atients were misinterpreted as desmoid tumor (one patient) and squamou s cell carcinoma (two patients), respectively. Histologically, all tum ors were poorly circumscribed and composed of fascicles and bundles of spindle-shaped cells with hyperchromatic nuclei and associated with e xtensive stromal collagenization. Perineural invasion was noted in two tumors. An overlying, atypical, intraepidermal melanocytic proliferat ion was observed in two tumors. Immunohistochemically, all three tumor s showed positive immunoreactivity with S-100 protein and vimentin. On e tumor also expressed HMB-45. Wide surgical incision was the primary mode of therapy in all patients. One patient also received multiple co urses of radiation therapy and chemotherapy. One patient died of wides pread metastatic disease. CONCLUSIONS. DMM of the oral mucosa is a rar e, often unrecognized, form of malignant melanoma associated with a fi brosarcoma-like morphologic appearance and abundant collagenization. M eticulous attention to histomorphology and judicious use of immunohist ochemical stains will help prevent misdiagnosis. (C) 1996 American Can cer Society.