(P 147) CONVENTIONAL AND DEDIFFERENTIATED CHONDROSARCOMA; IS ENCHONDROMA THE PRECURSOR LESION?

Objective: Chondrosarcoma is the second most common primary malignant bone tumor after osteosarcoma. It is subclassified into conventional, dedifferentiated, clear cell, and mesenchymal types. Most (85%) chondrosarcomas are conventional hyaline/myxoid variants and 10% are dedifferentiated. Traditionally, conventional chondrosarcoma has been considered to develop de novo except in rare instances. We analyzed the prevalence of enchondroma in patients with conventional and dedifferentiated chondrosarcoma to determine the relationship between these neoplasms.

Methods: We identified 72 cases of intramedullary conventional and dedifferentiated chondrosarcoma from patients who underwent resection from our archives between 2014-2025. The electronic medical records were evaluated for demographic data and imaging findings. The histopathologic materials were reviewed for the presence of underlying enchondroma within the chondrosarcoma.

Results: There were fifty-seven cases (79%) of conventional chondrosarcoma (including three cases designated atypical cartilaginous neoplasm), and fifteen (21%) dedifferentiated chondrosarcomas. There was a slight male predominance (M: F=1.1). Patient’s ages ranged from 22 to 85 years (mean=58). Pelvic bones were the most frequently affected (27%) followed by the femur (20%), chest wall (rib/sternum 18%), humerus (16%), scapula (8%), tibia and fibula (5%), vertebrae (3%), and phalanx/metatarsal (3%). The size of the neoplasms ranges from 1.6 cm to 23 cm (median=6.9 cm). Thirty-three patients (46%) had a solitary enchondroma encompassed by chondrosarcoma. Among these, twenty-four (73%) were conventional and nine (27%) were dedifferentiated chondrosarcomas. The femur and humerus were the most common locations (36% and 24%, respectively) followed by pelvic bones (18%), and phalanx/metatarsal bones, tibia, scapula and vertebra (4% each). Three patients (4%) had enchondromatosis.

Conclusion: The prevalence of enchondroma in conventional and dedifferentiated chondrosarcoma is under-recognized in the literature. We demonstrate that nearly half of patients with conventional chondrosarcoma and dedifferentiated chondrosarcoma have an associated enchondroma. This observation is evidence that enchondroma is a precursor lesion that may undergo biological transformation into conventional and dedifferentiated chondrosarcoma.