Diagnosis of thoracic SMARCA4‐deficient undifferentiated tumor in cytology

Although alterations in SMARCA4‐deficient occur in non–small cell lung carcinoma (SD‐NSCLC), thoracic SMARCA4‐deficient undifferentiated tumor (TSDUT) is recognized as a distinct entity in the 2021 World Health Organization Classification of Thoracic Tumors because of unique morphologic, immunophenotypic and molecular features, and worse survival compared with SD‐NSCLC. Cytologic diagnosis of TSDUT is clinically important because of its aggressive behavior and because it is often diagnosed by fine‐needle aspiration because TSDUTs are usually unresectable at presentation. Here, we identify cytologic features that can be used for recognition of TSDUT and distinction from SD‐NSCLC.