CT imaging features of pulmonary SMARCA4-deficient undifferentiated carcinoma: a retrospective case series.

Background: Pulmonary SMARCA4-deficient undifferentiated carcinoma is a rare and highly aggressive thoracic malignancy characterized by rapid progression, poor prognosis, and nonspecific imaging features. Although its pathological and molecular characteristics are increasingly recognized, its CT imaging features remain insufficiently characterized. This study aimed to systematically describe the CT imaging features of this entity and to summarize coexisting imaging findings that may assist radiologic suspicion. Methods: This retrospective study included 15 patients with pathologically and immunohistochemically confirmed pulmonary SMARCA4-deficient undifferentiated carcinoma. All patients underwent baseline chest CT before any antitumor treatment, including non-contrast and contrast-enhanced scans. Two experienced thoracic radiologists, blinded to pathological results, independently evaluated tumor location, size, morphology, margins, intratumoral necrosis or cavitation, enhancement characteristics, invasion of adjacent structures, lymphadenopathy, pleural involvement, and distant metastases. Interobserver agreement was assessed using Cohen's κ, and analyses were descriptive. Results: Patients were predominantly middle-aged to elderly men, most with a smoking history, and the majority presented with locally advanced or advanced-stage disease. On CT, tumors typically appeared as solid masses with a median maximum diameter of 3.7 cm (range, 0.6-9.5 cm), nearly half of which were centrally located. Aggressive imaging features were common, including spiculated margins (93.3%), intratumoral necrosis (86.7%), and cavitation (46.7%). Contrast-enhanced CT frequently demonstrated heterogeneous moderate-to-marked enhancement. Invasion of adjacent structures was prevalent, including bronchial involvement (86.7%), vascular invasion (80.0%), and mediastinal invasion (66.7%). Lymph node metastases were observed in 86.7% of cases, often as conglomerated lymphadenopathy (73.3%). Key imaging features showed good-to-excellent interobserver agreement. All cases demonstrated loss of SMARCA4 (BRG1) nuclear expression with retained INI-1. Conclusion: Pulmonary SMARCA4-deficient undifferentiated carcinoma showed a reproducible aggressive CT imaging profile in this cohort, characterized by marked heterogeneity, necrosis or cavitation, multi-structure invasion, and conglomerated lymphadenopathy. Although these findings are not individually specific, their co-occurrence may help raise suspicion for this entity over other aggressive thoracic malignancies with overlapping imaging features and support earlier targeted immunohistochemical confirmation. Further multicenter studies are needed to validate this CT imaging profile and clarify its clinical relevance.