The WHO Reporting System for Soft Tissue Cytopathology is Volume 4 of this series of reporting systems for cytopathology, which is a joint project of the International Academy of Cytology (IAC) and the International Agency for Research on Cancer (IARC), a specialized agency of the World Health Organization (WHO). The series includes a unique synthesis of the published evidence and the practice of cytopathology, and it is linked to the WHO Classification of Tumours series, now in its 6th edition. Cytopathologists look at tumors slightly differently than other specialists do, and there is a need for specializedreporting systems based on the key diagnostic cytopathological features of tumors, presented in standardized reports, within a hierarchical system of diagnostic categories. These categories must also be linked to diagnosticmanagement recommendations to improve communication with clinicians and support patient care. And it is essential that these reporting systems be truly international, to serve the needs of patients worldwide in many differently medically resourced settings. What are the key features of this first edition of the series? These volumes are an essential tool for standardizing diagnostic cytopathology practice worldwide and will serve as a vehicle for the translation of cytopathology research into practice. The key diagnostic cytopathological features listed for each tumor type under the diagnostic categories represent the first international consensus and are described in precise, uniform language. These diagnostic criteria are underpinned by available evidence that has been evaluated and debated by experts in the field.

Lesion-specific sections include discussion of the differential diagnosis of the lesions' cytopathological features that can be used worldwide, especially in low-resource settings, followed by a discussion of the current best-practice application of ancillary testing on cytopathology material. This volume Prepared by about 40 authors and editors Contributors from around the world, reflecting an international expertise Hundreds of high-quality images More than 1500 references Online version The content of this new, innovative, and comprehensive cytopathology reporting series is also availablein a convenient digital format, at https://tumourclassification.iarc.who.int.