Immunohistochemical localization of S-100 protein in granular cell myoblastoma.

The presence and distribution of S-100 protein were studied in three cases of granular cell myoblastoma using the peroxidase-anti-peroxidase method. Positive immunostaining was observed in all cases. The densely brown reaction products were found both in the nuclei and in the cytoplasm of myoblastoma cells. The staining of the nuclei was more intense than that of the cytoplasm. In addition, both normal Schwann cells and tumor cells of Schwannomas were also stained with anti-S-100 antibody. This result further supports the concept of the neurogenic origin of the granular cell myoblastoma.