Embryonal rhabdomyosarcoma with a der(16)t(1;16) translocation

Embryonal rhabdomyosarcoma (ERMS) is the most common subtype of RMS that predominantly involves the genitourinary tract and the head and neck regions in children younger than 10 years of age. Cytogenetically, ERMS is most frequently hyperdiploid, with extra copies of chromosomes 2, 7, 8, 11, 12, 13, and 20. No consistent structural chromosomal alteration has been identified in ERMS. In contrast, a t(2;13)(q35;q14) or t(1;13)(q36;q14) corresponding to PAX3–FOXO1A (previously FKHR) and PAX7–FOXO1A gene fusions are considered tumor-specific anomalies for alveolar RMS (ARMS). Occasionally, a recurrent secondary structural rearrangement involving chromosomes 1 and 16 is seen in translocation-positive ARMS, a der(16)t(1;16) resulting in an imbalance of 1q and 16q material. Conventional cytogenetic analysis of an ERMS arising in the urinary bladder of a 22-month-old male child revealed this nonrandom secondary chromosomal aberration, der(16)(1;16)(q22;q24), in a hyperdiploid complement with extra copies of chromosomes 2, 7, 8, 10, 12, 13, 19, and 20. Subsequent analyses showed tumor cells to be negative for FOXO1A, PAX3, or PAX7 gene locus rearrangements (by fluorescence in situ hybridization) and also negative for PAX3–FOXO1A and PAX7–FOXO1A fusion transcripts (by reverse transcriptase–polymerase chain reaction). These results suggest that the unbalanced t(1;16) translocation may be seen in RMSs lacking a primary genetic rearrangement.