Immunohistochemistry is crucial for achieving a correct diagnosis, especially on small biopsies, as virtually no bland-looking spindle cell sarcoma is diffusely and strongly stained with S100 protein and/or SOX10; typically, the nuclear expression of H3K27me3 is retained, and the lack of expression of epithelial and myogenic markers as well as CD117/DOG1 is useful in the differential diagnosis with other tumor entities, such as synovial sarcoma, leiomyosarcoma, and GIST, respectively. The gene discussed is SOX10; the disease is neoplasm.