Novel ALK-EML4 fusion with prominent mucous and hyaline stroma: Expanding the molecular genetic spectrum of S100 and CD34 positive spindle cell tumor

We report a case of a 49-year-old male patient suffering from an intraspinal tumor in the lumbar vertebra. The neoplasm was composed of mono-morphic spindle cells, arrayed in a patternless pattern in a background of prominent myxoid hyaline stroma with perivascular collagen rings in hyper-cellular regions. Instead, aggregated collagen fibers arranged into nodules and apparent calcium deposition were found in hypo-cellular regions. The tumor cells showed immunopositivity with S100 and CD34, whereas lacked SOX10 expression, which were reminiscent of a group of S100 and CD34 co-expression soft tissue spindle cell lesions having recurrent fusions including RAF1, BRAF, NTRK1/2/3, and RET genes. Interestingly, a novel anaplastic lymphoma kinase (ALK)- echinoderm microtubule-associated protein-like 4 (EML4) gene fusion was revealed. To our best knowledge, it was the first time to identify such gene fusion in the Orientals among this mentioned group, and it expands the molecular genetic spectrum of this specific group. The clinical relevance of this novel fusion requires further investigations.