Dermatofibrosarcoma protuberans and its fibrosarcomatous variant with areas of myoid differentiation: a report of three cases

Aims We describe three examples of dermatofibrosarcoma protuberans which demonstrated focal myofibroblastic differentiation, and discuss the nature of myofibroblastic differentiation. Methods and results We studied three cases of dermatofibrosarcoma protuberans, two of which had fibrosarcomatous portions containing myoid areas, and one which showed myoid areas in ordinary dermatofibrosarcoma protuberans. Myoid areas were recognized histologically as randomly distributed, scattered bundles or small nodules of spindle cells with deeply eosinophilic cytoplasm. Myofibroblastic differentiation was demonstrated immunohistochemically by positive staining for smooth muscle actin and muscle-specific actin, and ultrastructurally by the presence of microfilament bundles with focal dense bodies and pinocytic vesicles. The myoid areas occasionally contained intraneoplastic blood vessels. Conclusion The presence of myoid areas may be related to reactive hyperplasia of stroma, and its relation to the histogenesis of dermatofibrosarcoma protuberans is uncertain.