Low-grade fibromyxoid sarcomas are rare, histologically deceptive, cytologically bland tumors that are infrequently encountered in pediatric patients. Our knowledge of histologic spectrum of these tumors is limited. A histologically unusual variant of a low-grade fibromyxoid sarcoma arising in a 3-year-old boy and containing islands of cohesive epithelioid cells is described. The diagnosis was, given the patient's age and the presence of epithelioid islands, very difficult and was verified by the presence of 3-way chromosomal translocations involving 7q34, 10q11.2, and 16p11.2 by rearrangement of the FUS gene and by immunoreactivity for mucin 4.

The first case of large cell neuroendocrine carcinoma arising in an infant is presented. The tumor arose at the anal verge of a 1-year-old girl. The diagnosis of this CD99-positive tumor was supported by expression of epithelial (keratins, EMA, and Ep-CAM) and neuroendocrine (chromogranin A, synaptophysin, and neuron-specific enolase) markers and absence of immunoreactivity for Fli-1. No fusion of EWSR1 with FLI-1 or ERG was detected by polymerase chain reaction. However, the split of the EWSR1 gene was demonstrated by fluorescence in situ hybridization. This case adds to the few epithelial tumors in which an EWSR1 rearrangement was demonstrated. Because the tumor was initially misclassified as an extraskeletal Ewing's sarcoma, the patient was treated according to the Ewing's sarcoma treatment protocol. She remains free of tumor 8 years after initial diagnosis.