Cytokeratin-, calponin-, and p63-positive chondroblastoma with extensive soft tissue involvement and vascular invasion: a potential diagnostic dilemma

Chondroblastomas are rare bone tumors, accounting for less than 2% of all bone tumors. Although generally benign, there are instances of aggressive tumor behavior with extensive soft tissue invasion and even metastasis. In this report, we detail an instance where the tumor displayed extensive soft tissue invasion. As there is tumor heterogeneity in terms of morphologic appearance as well as a varied immunohistochemistry profile, a diagnosis of chondroblastoma may not be straightforward if the initial biopsy sample did not include the more characteristic area. In our case, the tumor expressed cytokeratin, calponin, and p63 in addition to S-100, potentially raising a diagnosis of a mixed tumor. The differential diagnosis and biologic behavior of chondroblastomas are discussed.