PATH-40. A GIANT CELL LESION RESEMBLING REPARATIVE GIANT CELL GRANULOMA WITH FN1-TEK FUSION, IN THE SPECTRUM OF CALCIFIED CHONDROID MESENCHYMAL NEOPLASM?

Abstract A newly described entity called “calcified chondroid mesenchymal neoplasms” includes neoplasms with variable amounts of calcification and FN1 fusions [Liu et al, Mod Pathol 2021]. We report a case left temporal bone giant cell granuloma-like lesion that also shows an FN1-TEK fusion. Close monitoring MRI images after surgery has showed no recurrence. Case report: 33-year-old male developed jaw pain he was diagnosed temporomandibular joint disorder. He felt ear fullness 2 years later experienced severe swelling in the region. Imaging expansile osseous multi-cystic components involving sphenoid as well all portions including mastoid, middle cavity, glenoid fossa. Pathology hemorrhagic negative for H3G34W mutation USP6 rearrangement, suggesting reparative granuloma. subsequent NGS Tempus 648 gene panel did not identify somatic or germline mutations, but additional RNA fusion test found possibility neoplasia. brain over past 9 months shown signs DISCUSSION recent small series describes novel calcified neoplasm FN-1 one case. The FIN1-TEK prominent cells. It is unclear whether lesions belong spectrum are separate non-neoplasm shares same alteration. More studies warranted.