Prolonged survival of thoracic SMARCA4-deficient undifferentiated tumor with immune-related cystitis: a case report and literature review.

Thoracic SMARCA4-deficient undifferentiated tumor (SMARCA4-UT), as a rare and highly malignant neoplasm associated with a high mortality risk, is easily confused with SMARCA4-deficient nonsmall-cell lung cancer (NSCLC). To date, no standard and effective protocol for thoracic SMARCA4-UT has been established. Immunotherapy has demonstrated efficacy in advanced NSCLC, achieving unprecedented survival benefits. However, immune-related adverse events (irAEs) remain a significant clinical challenge. Here, we reported the first case of thoracic SMARCA4-UT with immune-related cystitis and hypothyroidism, in which the patient benefited from first-line immune checkpoint inhibitor (ICI)-based combination therapy, achieving a remarkable overall survival of over 100 weeks. Furthermore, we performed a review and analysis of the diagnosis, differential diagnosis, immunotherapy, and prognosis of thoracic SMARCA4-UT, proposing that first-line therapy combining immunotherapy with platinum-based chemotherapy (induction and maintenance phases) with or without radiotherapy, may improve the prognosis of such patients. Additionally, we hypothesized a potential role of macrophages in the pathogenesis of immune-related cystitis for the first time and detailed the clinicopathological characteristics and evidence-based management of this irAE.