Embryonal Rhabdomyosarcoma with Posttherapy Cytodifferentiation and Aggressive Clinical Course.

Rhabdomyosarcoma is the most common soft tissue sarcoma in children and adolescents. Embryonal rhabdomyosarcoma (ERMS), its most common subtype, is a malignant soft tissue tumor with morphologic and immunophenotypic features of embryonic skeletal muscle. The histologic findings in ERMS typically include a range of differentiation in rhabdomyoblasts from primitive to terminally differentiated forms, and the latter become more prominent after chemotherapy-induced cytodifferentiation. Several reports have shown therapy-related cytodifferentiation to portend a good prognosis in ERMS. We discuss the case of a pediatric patient who presented with ERMS of the orbit. Although her tumor showed extensive posttreatment cytodifferentiation and several other good prognostic clinicopathologic factors, it pursued an aggressive course, resulting in early metastasis and death. This case represents an unusual course and may be instructive as to the clinicopathologic features impacting prognostication, and ultimately the biology, of this aggressive family of tumors.