Malignant melanoma of the nasal cavity.

We report a case of amelanotic melanoma arising in the nasal cavity and paranasal sinuses, that could not be positively diagnosed as malignant melanoma before the patient's death in spite of repeated biopsies both from primary and metastatic lesions, including ultrastructural examination and immunohistochemical staining for S-100 protein with usual polyclonal antibody. The patient died of rapid wide-spread dissemination of the tumor. In autopsy specimens, melanin pigment was detected, for the first time, by the Fontana's silver stain. The posthumous diagnosis of malignant melanoma was immunohistochemically confirmed for the specific antibodies, anti alpha-subunit of S-100 protein antibody and SK-46 (original antibody for melanoma made at the Department of Pathology, University of Gunma School of Medicine) from specimens obtained while alive. The application of a specific antibody for S-100 protein is recommended as useful for the diagnosis of malignant melanoma even when routine immunohistochemical procedures fail to demonstrate S-100 protein.