Diagnosis of thoracic SMARCA4‐deficient undifferentiated tumor in cytology

Abstract

AbstractIntroductionAlthough 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.Materials and MethodsCytomorphologic features were investigated in cytology specimens from patients with TSDUT (n = 11) and compared with a control group of patients with SD‐NSCLC (n = 20).ResultsThe presence of classic rhabdoid morphology, at least focally, was entirely specific for TSDUT (n = 6, 55%) compared with SD‐NSCLC (n = 0) in this study. TSDUT more frequently showed tumor necrosis (n = 11, 100% vs. n = 8, 40%; p = .001), dominant single‐cell pattern on aspirate smears or touch preparation slides (n = 8 [of 9], 80% vs. n = 3, 15%; p = .010), nuclear molding (n = 5, 45% vs. n = 1, 5%; p = .013), and indistinct cell borders (n = 11, 100% vs. n = 5, 25%; P < .001) compared with SD‐NSCLC, respectively.ConclusionsCytomorphologic features occurring more frequently in TSDUT include tumor necrosis, dominant single‐cell pattern, nuclear molding indistinct cell borders, and focal rhabdoid cells. Presence of these features in a cytology specimen of an undifferentiated tumor, particularly in a patient with a thoracic mass, should raise suspicion for TSDUT and prompt appropriate ancillary workup.