[Clinical characteristics and prognostic analysis of thoracic SMARCA4-deficient undifferentiated tumor]

Objective: To summarize and analyze the clinical characteristics and prognosis of thoracic SMARCA4-deficient undifferentiated tumor (SMARCA4-UT). Methods: A retrospective analysis was conducted on the clinical data of 51 patients with SMARCA4-UT who were diagnosed in the First Affiliated Hospital of Zhengzhou University from January 2018 to December 2023, and 52 patients with SMARCA4-intact non-small cell lung cancer (SMARCA4-iNSCLC) expression admitted during the same period were used as controls. The Kaplan-Meier survival analysis and log-rank test were used to analyze the survival difference between the two groups of patients, and the Cox regression model was used to explore the factors influencing the prognosis of the two groups of patients. Results: In the SMARCA4-UT group, there were 50 males and 1 female, with the age of (63.8±9.7) years. Compared to the SMARCA4-iNSCLC group, the SMARCA4-UT group exhibited a higher proportion of male patients and smokers, as well as a higher Ki-67 level (all P<0.05). SMARCA4-UT is mainly characterized by solid lesions with poor adhesion, and some of them exhibit rhabdomyoid morphology. Immunohistochemistry revealed negative results for BRG1, thyroid transcription factor-1, P40, NapsinA, and others were mostly negative, while some patients were positive for spalt-like transcription factor 4. There were a relatively large number of cases with Ki-67≥30% (47/51, 92%). Among the 10 patients in the SMARCA4-UT group who underwent next-generation sequencing genetic testing, 6 patients were found to have SMARCA4 mutations, often accompanied by TP53 (8/10, 80%), STK 11(3/10, 30%), KRAS(2/10, 20%), with fewer common driver gene mutations. The average tumor mutation burden was 16.12 mutations/Mb. Compared with SMARCA4-iNSCLC patients, the median overall survival of SMARCA4-UT patients was significantly shorter (12 months vs 45 months, P<0.001), and the median overall survival of patients with stage Ⅲ-Ⅳ SMARCA4-UT treated with immunotherapy was longer than that of patients without immunotherapy (23 months vs 7 months, P=0.027). The results of the multivariate Cox regression model analysis indicated that SMARCA4 deficiency is a risk factor for prognosis in patients with SMARCA4-UT and SMARCA4-iNSCLC [HR=7.954(95%CI： 2.764-22.890), P<0.001]. Conclusions: SMARCA4-UT is a rare undifferentiated tumour distinct from SMARCA4-iNSCLC, which is prevalent among elderly male smokers. It possesses high invasiveness and poor prognosis. The typical pathological characteristic is negative BRG1. Immunotherapy demonstrates a certain effect.