Soft tissue Langerhans' cell histiocytosis in an adult. A case presentation with flow cytometric analysis and literature review.

We report a case of solitary unifocal Langerhans' cell histiocytosis presenting as a large lower extremity soft tissue mass in a 48-year-old white man. Radiologically, this was an infiltrating mass involving all compartments of the right thigh; the mass had a maximum diameter of 18 cm. Extensive evaluation revealed no evidence of involvement of any other organ. An incisional biopsy was performed under the presumptive clinical impression of sarcoma. A definitive diagnosis of Langerhans' cell histiocytosis was established on the basis of characteristic morphologic features, cell surface marker findings by immunohistochemistry and flow cytometry, and electron microscopic studies. The patient was treated with four courses of chemotherapy, (etoposide and prednisone) and had no evidence of disease 3 years after the initial presentation. A review of the literature revealed that soft tissue Langerhans' cell histiocytosis usually presents in the head and neck area of children and usually has associated bone, lung, or reticuloendothelial system involvement. To our knowledge, this is the first reported case of solitary Langerhans' cell histiocytosis in an adult in which the presentation mimicked sarcoma.