Abstract
Spindle cell rhabdomyosarcoma (SC-RMS) is a rare tumor,accounting for 5-10 % of all cases of rhabdomyosarcomas. Diagnosis of SC-RMSmay be difficult because it mimics other malignant spindle cell lesions,including leiomyosarcoma.
SC-RMS is characterized by expression of desmin, withmost cases also expressing smooth muscle actin. Scattered rhabdomyoblasts orcross-striated cells may be a clue to a correct diagnosis.
Immunohistochemicaldemonstration of myogenic transcription factors (myogenin, MyoD1) confirms the diagnosis.Prognosis of SC-RMS depends on age, site of involvement and, most importantnly,on underlying genetic abnormalities; MyoD1-mutatedcases are associated with poor outcomes, while cases with translocationsinvolving VGLL2 or NCOA2 genes have excellent prognosis.