Patient characteristics and clinical findings
| Number | Sex | Age (years) | Site | Diagnosis | Microscopy | USP6 fusion partner | Ki-67 |
| 1 | F | 10–15 | Clavicle | ABC | Fibrous tissue with foci of calcified osteoid. Pseudocystic spaces without inner lining. Areas of hypercellular tissue with giant multinucleated cells and iron pigment. | CDH11::USP6 | 2% |
| 2 | M | 5–10 | Mandible | ABC | Short fascicles of elongated cells with oval nuclei (no atypia). Varying number of giant multinucleated cells. Local extravasation of erythrocytes. Bone trabeculae predominantly around margins. Area of adjacent skeletal muscle infiltration. | CDH11::USP6 | 5% |
| 3 | F | 40–45 | Distal phalanx of right-hand finger | ABC - solid variant | Proliferation of short spindle cells without atypia. Plentiful admixture of giant multinucleated osteoclast-like cells. Abundant vascularisation present. No distinct pseudocystic spaces nor haemosiderin deposits. | EIF1::USP6 | 15% |
| 4 | M | 50–55 | Distal phalanx of left-hand finger | ABC | Subungual mass of polypoid tumour with pseudocystic changes. Mononuclear spindle cells with bland nuclei and plenty of multinucleated giant osteoclast-like cells. Areas of newly formed woven bone with small deposits of haemosiderin. Pseudocystic spaces are focally filled with blood. Exculceration of polypoid convexity with fibrin and polymorphonuclear cells at base with granular tissue formation. No nuclear atypia. | ZFX::USP6 | 10% |
| 5 | F | 25–30 | Rib | ABC | Lamellar bone tissue and fragments of fibroadipose tissue with areas of spindle cells without atypia. Giant multinucleated cells are also present. | COL1A2::USP6 | 5% |
| 6 | M | 15–20 | C7 (posterior elements and body) | ABC | Uniform population of oval mononuclear cells and giant osteoclast-like elements with excess nuclei. Mitotic activity visible, but no atypical mitoses present. Areas of collagen-rich stroma. Short fascicles of spindle cells. Pseudocystic spaces engorged with blood in the centre of the lesion. Septa contain immature osteoid. Periphery of lesion with regressive changes of bone and cartilaginous tissue. | MEF2A::USP6 | 10% |
| 7 | F | 10–15 | C4 (dorsal part) | ABC | Solid and partially cystic lesion consisting of uniform population of oval mononuclear cells without atypia and disperse giant osteoclast-like elements. Pseudocystic spaces are filled with blood and formation of new bone detected at the periphery of the lesion. | IP6K2::USP6 | 2% |
ABC, aneurysmal bone cyst; F, female; M, male.