Occult Langerhans Cell Histiocytosis in Clear Cell Renal Cell Carcinoma

Langerhans cell histiocytosis is a rare disease that is characterized by a localized or systemic proliferation of Langerhans dendritic cells and a wide spectrum of clinical presentations. We experienced an unusual case of occult Langerhans cell histiocytosis associated with clear cell renal cell carcinoma. A 62-year-old man underwent a partial nephrectomy for left renal mass. Histologic examination showed nests of clear cells with surrounding thin-walled vessel that were suggestive of clear cell renal cell carcinoma. A well-defined nodule composed of atypical mononuclear cells and plentiful eosinophils presented within clear cell renal cell carcinoma. The mononuclear cells were Langerhans cell histiocytes with S-100 and CD1a immunoreactivity. On follow-up comprehensive physical, laboratory, and radiologic examination, there were no other lesions of Langerhans cell histiocytosis.