Peculiar chondroblastoma involving multiple tarsal bones.

A case of peculiar chondroblastoma involving multiple tarsal bones in a 49-year-old woman is described. The patient presented with pain and swelling of the right foot. Radiographs revealed a lytic expansile lesion of medial, intermediate, and lateral cuneiform bones, navicular, cuboid, and tarsal bones of the right foot, indicating a malignant tumor. Biopsies demonstrated a diffuse proliferation of round cells with eccentric and indented nuclei with longitudinal grooves and eosinophilic cytoplasm. Atypia was prominent, but mitotic figures were rare. The stroma was chondroid with focal chicken-wire calcification. On electron microscopy, the tumor exhibited chondroblastic features. The patient is alive with the tumor 7 years after radiotherapy. The tumor is considered a chondroblastoma with low malignant potential.