Aggressive chondroblastoma. Report of a case with multiple bone and soft tissue involvement.

A 14-year-old male had a recurrent chondroblastoma in his right talus which involved the right calcaneus and the soft tissue of that ankle. While the initial lesion had a typical, benign appearance, the recurrent lesion and the soft tissue nodules showed a significantly elevated mitotic rate. Although some extraosseous involvement by chondroblastomas may be secondary to soft tissue or hematogeneous seeding at the time of surgery, and aggressive variant of chondroblastoma appears to exist. Previous reports of these aggressive cases show a poor correlation between histologic appearance and biologic behavior. When objective quantitation of cytologic features such as mitotic rate are made, we believe that these features may serve as a marker for identification of those cases of chondroblastoma which have a propensity for aggressive behavior.