Chondroblastic osteosarcoma: Cytomorphologic characteristics and differential diagnosis on FNA.

BACKGROUND: Chondroblastic osteosarcoma (COS) is a uniformly fatal bone malignancy if not diagnosed and treated appropriately in a timely manner. Fine-needle aspiration (FNA) of osseous lesions is routinely performed in major medical centers. Appropriate characterization of the tumor will significantly influence patient management and outcomes.

METHODS: A retrospective review of the cytopathology archives of 2 large tertiary care centers for a 15-year period (2001-2015) revealed 17 cases of COS (9 primary, 6 recurrent, and 2 metastatic cases) in 16 patients. Clinical outcome and histopathologic follow-up were reviewed and correlated.

RESULTS: There were 9 male and 7 female patients (male-to-female ratio of approximately 1:1), ranging in age from 12 to 70 years (mean age, 29.2 years). The classic locations for osteosarcoma were commonly involved, such as the long bones around the region of the knee in 4 cases and the proximal humerus in 1 case. However, other "nonclassic" sites also were noted to be commonly involved, including the distal tibia or fibula (4 cases), sacroiliac region (4 cases), mandible (3 cases), and skull (1 case). Cytomorphologic characteristics were high cellularity; predominantly discohesive, single cells; small tissue fragments; background osteoid and chondroid matrix; spindled cells and plasmacytoid cells with moderate to abundant basophilic vacuolated cytoplasm and occasional multiple cytoplasmic processes; round to oval nuclei with anisonucleosis; and small to prominent nucleoli. There were scattered binucleated and multinucleated osteoclast-like giant cells. Cases with high-grade morphology demonstrated marked pleomorphism and abundant mitoses.

CONCLUSIONS: The differential diagnosis of COS includes chondroblastoma, chondrosarcoma, and chondroid chordoma. A definitive diagnosis can be made with clinical and radiological correlation. Cancer Cytopathol 2016;124:493-500. © 2016 American Cancer Society.