Unusual histologic variant of a low-grade fibromyxoid sarcoma in a 3-year-old boy with complex chromosomal translocations involving 7q34, 10q11.2, and 16p11.2 and rearrangement of the FUS gene.

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.