Sclerosing rhabdomyosarcoma of the oral floor mimicking a salivary gland tumor: A case report with immunohistochemical and genetic analyses

Sclerosing/spindle cell rhabdomyosarcoma (SRMS) is a rare type of rhabdomyosarcoma. We immunohistochemically and genetically examined a case of SRMS of the oral floor. The patient was a 19-year-old female, who noticed swelling in the right oral floor. Under a diagnosis of a sublingual tumor, tumor resection was performed. The tumor consisted of atypical round to short spindle-shaped cells that exhibited a hyalinized stroma and a trabecular growth pattern. The tumor cells were diffusely positive for vimentin, MyoD1, and bcl-2, whereas they were partially positive for desmin, cytokeratin (CK)7, CK5/6, and MDM2. They were negative for pan-CK, S-100 protein, and CD99(MIC2). Fluorescence in situ hybridization analysis did not detect any FOXO1A or NCOA2 gene split signals. The cancer cells harbored a point mutation in codon 122 of the MYOD1 gene. This case was finally diagnosed as SRMS. We discuss the differentiation of SRMS from salivary gland tumors.