Abstract
BACKGROUND: SMARCA4-deficient undifferentiated thoracic tumor (SMARCA4-UT) is a rare malignant condition with high invasiveness and poor prognosis. Presently, no clear guidelines are available for the treatment of SMARCA4-UT. The median overall survival was only four to seven months. Several patients are diagnosed in advanced stages of the malignancy and do not respond to conventional radiotherapy and chemotherapy. CASE DESCRIPTION: A 51-year-old Chinese man was diagnosed with a SMARCA4-UT. The patient did not have a chronic history of hypertension or diabetes and any family history of malignant tumors. No sensitive mutation in lung cancer-related ten genes was identified. The first-line therapy with four cycles of liposomal paclitaxel and cisplatin combined with two cycles of tyrosine kinase inhibitor anlotinib failed. On immunohistochemical analysis, no programmed cell death 1 ligand 1 (PD-L1) expression was found. However, whole-exon sequencing revealed a high tumor mutation burden (TMB) of 15.95 mutations/Mb with TP53 and KEAP1 mutations. The patient was treated with a second-line regimen containing tislelizumab, etoposide, and carboplatin (TEC). A reduction in tumor burden was seen for more than 10 months. CONCLUSIONS: The case of SMARCA4-UT with a high mutation burden successfully responded to the combined regimen containing TEC. This could be a new treatment option for patients with SMARCA4-UTs.