Two molecularly confirmed cases of extraskeletal myxoid chondrosarcoma illustrate its morphological spectrum and clinicopathological variability

Extraskeletal myxoid chondrosarcoma (EMC) is a rare soft tissue sarcoma characterised by recurrent NR4A3 gene rearrangements. Although classic EMC exhibits distinctive morphological features, cellular variants may show increased cellularity, reduced myxoid stroma, and focal solid growth, creating substantial diagnostic challenges and overlap with other soft tissue neoplasms. We report two molecularly confirmed EMC cases illustrating conventional morphology and focal cellular and solid features, and discuss the associated diagnostic challenges and clinicopathological implications. Case 1 involved a 72-year-old woman with a rapidly enlarging mass in the right thigh. Histological examination demonstrated conventional EMC with focal hypercellular areas showing solid growth and epithelioid morphology, accounting for approximately 30% of the tumour. Fluorescence in situ hybridisation (FISH) confirmed NR4A3 rearrangement. The patient underwent wide local excision followed by adjuvant radiotherapy and remained free of recurrence or metastasis during 15 months of follow-up. Case 2 involved a 38-year-old man with a tumour arising in the right popliteal fossa. The lesion exhibited typical EMC morphology with abundant myxoid stroma and a multinodular architecture. NR4A3 rearrangement was likewise confirmed by FISH. Following simple excision without adjuvant treatment, the patient developed a local recurrence in the right popliteal fossa and a separate, pathologically confirmed soft-tissue metastasis in the ipsilateral thigh within 6 months. These cases highlight the morphological spectrum of EMC and underscore the diagnostic value of NR4A3 rearrangement testing, particularly in tumours with atypical cellular and solid features. Integration of morphology, immunohistochemistry, and molecular findings is essential for accurate diagnosis. The different clinical courses of the two patients should be interpreted cautiously because of differences in tumour characteristics, surgical management, and follow-up duration.