UNDIFFERENTIATED SARCOMAS OF CHILDREN - PATHOLOGY AND CLINICAL BEHAVIOR - AN INTERGROUP RHABDOMYOSARCOMA STUDY

Undifferentiated soft tissue sarcoma (UND-STS) is the most poorly defi ned tumor eligible for Intergroup Rhabdomyosarcoma Studies (IRS). Rece nt IRS UND-STS experience was reviewed to assess the histologic charac teristics and clinical behavior of undifferentiated sarcomas. Of the 1 ,527 patients entered on IRS-III and IRS pilot-IV, 96 had tumors class ified by the IRS Pathology Committee as UND-STS. Of these, 52 had adeq uate histologic material for this study. After application of immunohi stochemistry, 18 tumors were reclassified, mostly as embryonal rhabdom yosarcomas (RMS), primitive neuroectodermal tumors, and intraabdominal desmoplastic small round cell tumors. The remaining 34 UND-STS had a diffuse hypercellular histologic pattern made up of sheets of medium-s ized cells. The tumor cells had a minimal to moderate amount of cytopl asm and a variable nuclear morphology, predominately vesisular with fi nely granular chromatin. Except for reactivity with antibodies against vimentin, most tumors had a negative immunohistochemical profile. The 5 year Kaplan-Meier survival estimate for patients with non-metastati c disease was 72%, a significant improvement when contrasted with pati ents diagnosed to have UND-STS in IRS-I and IRS-III. (C) 1997 Wiley-Li ss, Inc.