Osteosarcomatous Changes in Malignant Melanoma Immunohistochemical and Ultrastructural Studies of a Case

Immunohistochemical and ultrastructural studies were conducted to elucidate the nature and origin of osteosar-comatous changes in malignant melanoma in a 43-year-old Japanese man. Immunohistochemical studies with the use of antisera against human S-100 protein and neuron-specific enolase demonstrated positive reactions in the tumor cells within the osteosarcomatous area. UI-trastructurally, the neoplastic cells showed marked similarities to those from osteosarcomas. Additionally, occasional neoplastic cells contained round or ellipsoidal os-miophilic organelles, presumably melanosomes. These findings indicate that osteosarcomatous changes in malignant melanoma are produced by the dedifferentiated melanoma cells.