The Small Round Cell Sarcomas Complexities and Desmoplastic Presentation

BACKGROUND: Small round cell sarcomas (SRCSs) account for most solid malignancies in the pediatric age group and are a part of group of malignant tumors characterized by heterogenous clinical presentation and overlapping microscopic features of small, round, primitive cells. In addition to the recently established certain genetically defined subset of undifferentiated round cell sarcomas of soft tissue and bone, this group of sarcomas include desmoplastic small round cell tumor, poorly differentiated synovial sarcoma, alveolar rhabdomyosarcoma, mesenchymal chondrosarcoma, and small cell osteosarcoma. Although, those entities share clinical and cytomorphologic features and cannot be unequivocally classified based on clinical presentation and morphology alone. Most of SRCSs characterizes of particular patterns of protein expression or genetic changes and ancillary tests remain necessary to confirm or rule out a specific diagnosis. Subtle but occasionally distinctive cytologic features narrows the number of differential diagnoses and helps to select appropriate ancillary tests necessary for the final diagnosis. Thus, when adequate fine needle aspiration (FNA) biopsy specimen is combined with ancillary tests, a specific histologic diagnosis can be made in almost all cases. However, due to complex cytologic features of SRCS as well as various quality and diversity of FNA smears, there are cases in that cytologic features which do not entirely match the known diagnostic criteria. SUMMARY: The aim of this review was to summarize cytomorphologic criteria and to present rare and divergent cytological features of SRCSs. Careful assessment of clinical presentation, cytological features, immunohistochemical patterns, and molecular alternations is necessary for an accurate diagnosis. Knowing of rare and divergent microscopic findings that does not fit with the known cytological criteria will help to avoid misdiagnosis. KEY MESSAGES: The role of FNA biopsies diagnosing soft tissue and bone tumors has been increasing because of the ability of ancillary tests to assist in the diagnosis of specific tumors. SRCSs may be diagnosed accurately in cytology specimens. Access to clinical and radiographic presentation, utility of ancillary tests, understanding complexity of cytological features, and awareness of the rare cytologic findings that differ from that of the established diagnostic criteria are essential to make correct diagnosis.