[A case of amelanotic melanoma of the nasal cavity].

A 68-year-old male visited Hospital A for treatment of epistaxis, his chief complaint. He was told that he had an easily-bleeding tumor in the nasal cavity. Based of biopsy, a diagnosis of amelanotic melanoma was made. Operation was performed for removal of the tumor. About 8 months after discharge, he visited Hospital B with complaints of lumbar pain and epistaxis. After biopsy at Hospital B, malignant lymphoma (diffuse large cell) was diagnosed, and the patient was referred to our hospital. On bone marrow puncture and biopsy, tumor cell infiltration was observed. Flow cytometric surface marker analysis revealed that these tumor cells were negative for CD45. Results of HE staining of the nasal cavity tumor were insufficient for diagnosis, and staining by immunohistochemistry was necessary to confirm the diagnosis. On immunohistochemical staining of the nasal cavity tumor tissue and bone marrow biopsy tissue, LCA, L26 and UCHL-1 were negative, and S-100 and HMB-45 positive. Recurrence of amelanotic melanoma accompanied by bone marrow infiltration was therefore diagnosed. The incidence of amelanotic melanoma with primary lesions in the nasal cavity is low. However, in making the diagnosis of a nasal cavity lesion, the possibility of such a melanoma should be kept in mind. In many cases, it is difficult to diagnose amelanotic melanoma with HE staining alone, and immunohistochemistry must be used.