Sclerosing rhabdomyosarcomas in children and adolescents: a clinicopathologic review of 13 cases from the Intergroup Rhabdomyosarcoma Study Group and Children's Oncology Group.

In recent reports, investigators have described a variant of adult sclerosing rhabdomyosarcoma (RMS) that is characterized by a hyalinizing, matrix-rich stroma. To determine whether this variant occurs in children, we investigated this phenomenon in a recent series of 1207 pediatric patients who had RMS accessioned by the Intergroup Rhabdomyosarcoma Study Group, now part of Children's Oncology Group. Thirteen patients had features of sclerosing RMS; 9 had been diagnosed with alveolar RMS (ARMS), 3 with embryonal RMS (ERMS), and 1 with a spindle cell RMS. Primary sites included head and neck (6 patients), extremities (5 patients), scrotum (1 patient), and retroperitoneum (1 patient). Patients' ages ranged from 0.3 to 16 years. All tumors showed positivity for myogenin, MyoD, and desmin, but only 2 patients demonstrated the strong myogenin staining typically seen in ARMS. Three patients diagnosed with ARMS demonstrated embryonal-appearing foci, and 3 of 4 patients who had nonalveolar tumors had ARMS-like foci. Standard reverse transcriptase-polymerase chain reaction performed on RNA isolated from frozen sections showed 1 ARMS with a positivity for PAX3-FKHR with four patients classified as having ARMS and 1 as having spindle cell RMS were negative for both ARMS fusion transcripts (PAX3- and PAX7-FKHR). Cytogenetic testing in 2 patients who had ARMS-like foci demonstrated mild hyperdiploidy in both patients and a near-tetraploid clone in 1 patient. Sclerosing RMS may arise in children, have mixed ERMS-ARMS histology, originate from the head and neck, and lack strong myogenin staining.