Abstract
BACKGROUND: The SWI/SNF (Switch/Sucrose Non-fermentable) chromatin remodeling complex plays a critical role in regulating cellular transcription, and its dysfunction has been associated with the development of aggressive lung adenocarcinoma. The SWI/SNF complex comprises a variety of potential subunit combinations, including the ATP-dependent catalytic subunits SMARCA4 and SMARCA2. Notably, SMARCA4 deletions are observed in approximately 5-10% of lung adenocarcinomas. Conversely, SMARCA2-deficient and SMARCA4-preserved lung adenocarcinoma are relatively rare. CASE PRESENTATION: A 52-year-old woman presented with the complaints of persistent cough and dyspnea lasting for one week. Chest computed tomography demonstrated an irregularly shaped mass in the dorsal segment of the left lower lobe, accompanied with left pleural effusion and atelectasis. Cytological examination and cell block analysis revealed markedly atypical epithelial tumor cells exhibiting poor cohesion and rhabdoid morphological features. Immunocytochemical staining demonstrated positivity for Claudin4, TTF-1 and SMARCA4, while SMARCA2 expression was absent. Following these results, the pathological diagnosis was poorly differentiated lung adenocarcinoma with isolated SMARCA2 deficiency. Subsequently, next-generation sequencing (NGS) analysis identified a non-frameshift deletion in exon 19 of the EGFR gene. Based on these findings, target therapy with osimertinib was initiated, and the patient remained clinical stability for a duration of seven months following the initial presentation. CONCLUSIONS: The understanding of isolated SMARCA2-deficient lung adenocarcinoma remains limited, and no cases of this subtype diagnosed via cytology have been reported in the literature. The preparation of cell blocks combined with appropriate immunocytochemical staining represents a valuable and reliable diagnostic approach.