Abstract
RATIONALE: SMARCA4-deficient undifferentiated tumor (SMARCA4-UT) has emerged as a rare subtype of thoracic tumor, whose prognosis is unfavorable and for which standard therapeutic regimen is presently unavailable. PATIENT CONCERNS: This report details the case of a male thoracic SMARCA4-UT patient 60 years of age, who lacked the opportunity for surgery. Genomic analysis revealed a significant tumor mutational burden (15.95 muts/Mb). DIAGNOSES: The findings of computed tomography, histopathology, immunohistochemical staining, and genomic profiling led to the confirmation of a thoracic SMARCA4-UT diagnosis. INTERVENTIONS: The first-line treatment consisted of combination chemotherapy (carboplatin and etoposide), thoracic radiotherapy, and tislelizumab immunotherapy. The second-line treatment included radiotherapy for the right adrenal gland metastasis, combination chemotherapy (paclitaxel and cisplatin), and tislelizumab immunotherapy. OUTCOMES: As of July 2025, the patient's overall survival has exceeded 33 months. LESSONS: Our case of SMARCA4-UT exhibiting a high tumor mutational burden demonstrated a favorable response to the immunotherapy (tislelizumab) combined with chemotherapy and radiotherapy. This approach may represent a novel therapeutic strategy for SMARCA4-UT population.