Small round-cell neoplasms of soft tissues: An integrated diagnostic approach

The family of small round-cell tumours (SRCTs) represents a heterogeneous group of malignancies featuring a primitive, undifferentiated round-cell morphology. SRCTs mostly occur in children, adolescents and young adults, and tend to involve the skeletal system or soft tissue. They constitute approximately 20% of solid tumours in children and, because of their significant morphological overlap, have become a paradigm for an integrated approach to diagnosis. The combination of both immunophenotypic and genetic analysis with classic morphology has proved useful not only on diagnostic grounds, but also in the context of prognostication. This review will focus on SRCTs primarily involving soft tissues and includes the Ewing's family of tumours, also known as Ewing's sarcoma/primitive neuroectodermal tumour, alveolar rhabdomyosarcoma, desmoplastic SRCT, poorly differentiated round-cell synovial sarcoma and mesenchymal chondrosarcoma.