Citations

Giant cell tumor of bone (GCT) is a benign locally aggressive neoplasm composed of mononuclear cells admixed with innumerable osteoclast-type giant cells. H3F3A gene mutations producing mutant histone protein product H3.3 have been identified in 96% of GCT; mutant H3.3 is reliably demonstrated by immunohistochemistry. GCT may contain woven bone and rarely, neoplastic cartilage nodules which causes diagnostic challenges with aggressive neoplasms such as osteosarcoma. We describe the features of GCT with cartilage matrix and report the next-generation sequencing findings in a subset of tumors. Seventeen cases of GCT with cartilage matrix form the cohort: 7 males and 10 females, 13 to 55 (mean: 25) years old. Tumors involved the fibula (6), femur (6), and patella, tibia, humerus, S1, and scapula (1 case each). Tumors were radiolucent, circumscribed, lytic, and expansile. All contained classic GCT, foci of cartilage matrix, and trabeculae of woven bone. Immunohistochemistry showed diffuse staining for H3.3 in 9/9 cases and 1 case was positive for S100 and SOX9 in the cartilage areas. Next-generation sequencing showed a mutation in the H3F3A gene in 6/6 cases. On follow-up, 2 patients who underwent resection showed no disease after 12, and 7 months, respectively. Three patients had recurrences 10, 12, and 27 months after curettage; there were no metastases. GCT with cartilage matrix is uncommon. The cartilage matrix is associated with woven bone suggesting the neoplastic cells may differentiate into chondrocyte-like and osteoblast-like cells. Recognition of this neoplasm is important to prevent misdiagnosis and overtreatment of affected patients.

Pseudomyogenic hemangioendothelioma (PMH) is a well-recognized neoplasm that usually arises in the soft tissue; concurrent bone involvement occurs in 24% of cases. PMH of bone without soft tissue involvement is rare. We describe the clinicopathologic findings of 10 such cases, the largest series reported to date. The study included 9 male and 1 female patient; their ages ranged from 12 to 74 years (mean 36.7 y). All patients had multiple tumors with a distinct regional distribution: 45% restricted to the lower extremity; 25% to the spine and pelvis; and 15% to the upper extremity. On imaging studies the tumors were well circumscribed and lytic. The neoplasms were composed of spindled cells arranged in intersecting fascicles with scattered epithelioid cells; epithelioid cells predominated in 3 cases. The neoplastic cells contained abundant densely eosinophilic cytoplasm and vesicular nuclei. There was limited cytologic atypia and necrosis, few mitoses (0 to 2/10 high-power fields), and inconspicuous stroma. Unique findings included abundant intratumoral reactive woven bone and hemorrhage with numerous osteoclast-like giant cells. Immunohistochemically, most tumors were positive for keratin, ERG, and CD31; CD34 was negative. The balanced t(7:19)(q22;13) translocation was documented in 3 cases. Follow-up is limited, but no patient developed documented visceral dissemination, and all have stable or progressive osseous disease. PMH exclusively involving bone is rare. It is multicentric, often involves the lower extremity, and has unusual morphology. The differential diagnosis includes epithelioid vascular neoplasms, giant cell tumor, bone forming neoplasms, and metastatic carcinoma. Because of its rarity, unusual presentation, and morphology, accurate diagnosis can be challenging.