Pseudosarcomatous Myofibroblastic Tumor and Myosarcoma of the Urogenital Tract Immunohistochemical Characteristics and Differential Diagnosis

Objective.-Pseudosarcomatous myofibroblastic tumors (PMTs) of the urogenital tract are rare but distinctive lesions. Despite their benign behavior, they are frequently misinterpreted as leiomyosarcomas and rhabdomyosarcomas in preoperative biopsies and even in resected specimens because of their atypical spindle-cell features. Precise diagnosis of PMTs is important to avoid unnecessary radical therapy. We analyzed urogenital myoid tumors to clarify which of their characteristics are useful for the differential diagnosis. Methods.-We evaluated 7 urogenital myoid tumors consisting of 3 PMTs, 2 leiomyosarcomas, and 2 rhabdomyosarcomas. We studied the expression of various immunohistochemical muscle-cell markers including desmin, muscle-specific actin, α-smooth muscle actin, high-molecular-weight caldesmon, and myogenin. Results.-Desmin, muscle-specific actin, and α-smooth muscle actin were noted variably in all tumor types, whereas high-molecular-weight caldesmon was expressed only in leiomyosarcomas, and myogenin was expressed only in rhabdomyosarcomas. Conclusion.-High-molecular-weight caldesmon and myogenin are useful for differentiating urogenital PMTs from myosarcomas.