4.1 Article

Adamantinoma with a Prominent Spindle Cell Component Mimicking Intraosseous Synovial Sarcoma: Clinicopathological Features of Six Tumors

Journal

INTERNATIONAL JOURNAL OF SURGICAL PATHOLOGY
Volume 30, Issue 8, Pages 872-884

Publisher

SAGE PUBLICATIONS INC
DOI: 10.1177/10668969221117977

Keywords

adamantinoma; intraosseous synovial sarcoma; p63; p40; SS18 rearrangement

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This study presents six cases of adamantinoma with a prominent spindle cell component mimicking intraosseous synovial sarcomas. Clinical-radiological index of suspicion, immunostains (p63 and p40), and molecular tests are useful in accurately diagnosing adamantinomas with spindle cell morphology, which has treatment-related implications.
Introduction. Adamantinoma is sub-classified into classic/biphasic, osteofibrous dysplasia-like, and de-differentiated type. We present six adamantinomas with a prominent spindle cell component mimicking intraosseous synovial sarcomas. Methods. Six patients were either referred with a diagnosis of intraosseous synovial sarcoma or wherein synovial sarcoma was a differential diagnosis. Three tumors were tested for SS18 gene rearrangement by FISH and two for SS18::SSX fusion by RT-PCR technique. Results. There were three males and three females with an average age of 20.6 years. Radiologically, the lesions were expansile and showed lytic and/or sclerotic components, involving the cortex and/or medulla. Five lesions occurred in the tibia and two in the fibula. Two tumors displayed soft tissue extension and two occurred as multifocal lesions. Two patients were diagnosed with synovial sarcoma and a single patient with sarcomatoid carcinoma, elsewhere. Two in-house patients were initially diagnosed with synovial sarcomas. On review, all tumors were cellular comprising monomorphic spindle-shaped cells arranged in sheets and fascicles (n = 6), including a herringbone-like pattern (n = 3), focal tubules (n = 1), cohesive nests (n = 5), cords (n = 2), including pseudocystic component (n = 2). Immunohistochemically, tumor cells were positive for p63 (6/6), p40 (4/4), EMA (2/3), AE1/AE3 (5/6), various keratins (2/2), and TLE1 (2/4). Three tumors tested for SS18 rearrangement were negative, while two tumors tested for SS18::SSX fusion were negative. Conclusions. Adamantinomas with spindle cell morphology display overlapping features with synovial sarcoma. A clinico-radiological index of suspicion immunostains (p63 and p40) and molecular test for t(X; 18) translocation are useful in an exact diagnosis, which has treatment-related implications.

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