Application of ancillary studies in soft tissue cytology using a pattern-based approach

The cytologic diagnosis of soft tissue neoplasms has undergone many advances due to the development of numerous useful immunohistochemical markers and molecular assays that target specific molecular alterations. Ancillary tests, when used in conjunction with clinical, radiologic, and cytomorphologic features, allow for more accurate classification and refinement of differential diagnoses of soft tissue neoplasms. Soft tissue tumors encompass a diverse group of tumors showing a wide range of cytomorphologies that can be broadly grouped as lipomatous, myxoid, spindled, pleomorphic, round cell, and epithelioid. This pattern-based classification enables the formation of appropriate differentials; however, entities that share these basic morphologic patterns may vary greatly in their clinical behavior. The breadth of soft tissue tumors that can be diagnosed on cytologic preparations continues to increase with identification of defining molecular alterations that can be detected by conventional means (eg, fluorescence in situ hybridization) or by immunohistochemical surrogates. Furthermore, the emergence of high-throughput molecular techniques (eg, next generation sequencing) has potential roles for additional discovery and diagnostic applications. This review highlights the diagnostic role of ancillary tests in the context of a pattern-based approach to soft tissue cytology. Cancer Cytopathol 2018;000:000-000. © 2018 American Cancer Society.