Spindle cell malignant lymphoepithelial lesion of the parotid gland: clinical, light microscopic, ultrastructural, and in situ hybridization findings in one case.

Malignant lymphoepithelial lesions (MLEL) are rare tumors of the salivary glands that show high incidence in Inuit Canadians, Alaskans, and Greenland Eskimos. The tumors are usually anaplastic or poorly differentiated squamous cell carcinomas. Focal spindle cell elements have been rarely reported. The tumors have been epidemiologically linked to Epstein-Barr virus infection. We present a case of malignant lymphoepithelial lesion showing exclusive spindle cell morphology. The patient is a 44-year-old male Inuit Canadian who presented with a long-standing history of a left parotid mass. The mass did not show evidence of rapid growth or facial nerve involvement. Parotidectomy was performed. The tumor was histologically composed of spindle cells nodules in a background of lymphocytes. The spindle cells showed no evidence of cytologic atypia but were mitotically active. Immunohistochemical staining for low-molecular-weight cytokeratin was only focally positive. The differential diagnosis included a mesenchymal neoplasm and malignant lymphoepithelial lesion. Electron microscopic examination confirmed the squamous nature of the neoplasm. Intracytoplasmic viral particles were also identified ultrastructurally. In situ hybridization for Epstein-Barr virus mRNA using a 30-base oligonucleotide probe specific for the EBER-1 gene showed very high level of expression in the tumor cells. No expression was noted in the adjacent parotid gland tissue. Our findings confirm the squamous nature of malignant lymphoepithelial lesions despite the spindle cell morphology occasionally seen in these neoplasms. They also confirm the strong role of Epstein-Barr virus infection in the pathogenesis of these tumors. This may have further diagnostic and therapeutic implications.(ABSTRACT TRUNCATED AT 250 WORDS)