Round Cell Tumors of Bone: An Update on Recent Molecular Genetic AdvancesWei, Shi MD, PhD; Siegal, Gene P. MD, PhDAdvances in Anatomic Pathology: September 2014 - Volume 21 - Issue 5 - p 359–372 doi: 10.1097/PAP.0000000000000036 Review Articles Abstract Author Information Round cell tumors of bone are a divergent group of neoplasms that largely constitute Ewing sarcoma/primitive neuroectodermal tumor, small cell osteosarcoma, Langerhans cell histiocytosis, mensenchymal chondrosarcoma, and hematopoietic malignancies including lymphoma and plasmacytoma/myeloma, along with metastatic round cell tumors including neuroblastoma, rhabdomyosarcoma, and small cell carcinoma. These lesions share many histomorphologic similarities and often demonstrate overlapping clinical and radiologic characteristics, but typically have a diverse clinical outcome, thus warranting differing therapeutic modalities/regimens. Recent advances in molecular and cytogenetic techniques have identified a number of additional novel entities, including round cell sarcomas harboring CIC-DUX4 and BCOR-CCNB3 fusions, respectively. These novel findings have not only enhanced our understanding of the pathogenesis of round cell tumors, but also allowed us to reclassify some entities with potential therapeutic and prognostic significance. This article provides an overview focusing on recent molecular genetic advances in primary, nonhematologic round cell tumors of bone. Department of Pathology, University of Alabama at Birmingham, Birmingham, AL This work was supported in part by the Haley's Hope Memorial Support Fund for Osteosarcoma Research and the Thomas Logan RAID Fund for Ewing's Sarcoma Research at the University of Alabama at Birmingham. The authors have no conflicts of interest to disclose. Reprints: Gene P. Siegal, MD, PhD, Division of Anatomic Pathology, Department of Pathology, The University of Alabama at Birmingham, HSB 149K, 619 19th St. South, Birmingham, AL 35249 (e-mail: firstname.lastname@example.org). All figures can be viewed online in color at http://http://www.anatomicpathology.com. © 2014 by Lippincott Williams & Wilkins.