Long-term survival in SMARCA4-deficient undifferentiated lung carcinoma: a case report.

Background: SMARCA4-deficient undifferentiated lung carcinoma is a rare, highly aggressive tumor with a dismal prognosis and limited response to conventional therapies. This case report presented an exceptional instance of long-term survival exceeding 41 months in a patient with unresectable stage IIIA (T3N1M0) disease, to provide insights into potential therapeutic avenues for this challenging disease. Case Description: This article reports a case of a 51-year-old male patient diagnosed with SMARCA4-deficient undifferentiated carcinoma in the left upper lung lobe, unresectable stage IIIA (T3N1M0) disease. During the hospitalization, the patient received multimodal therapy combining chemotherapy, immunotherapy, and radiotherapy, followed by immunotherapy maintenance. Specifically, the patient underwent six cycles of induction therapy with the etoposide plus cisplatin regimen combined with sintilimab, followed by intensity-modulated radiation therapy (pGTV 48 Gy, pCTV 48 Gy), and subsequently received maintenance sintilimab monotherapy. Over a follow-up exceeding three years, the primary lesion completely disappeared, another lesion was significantly reduced and remained stable, with no distant metastases (such as brain, bone, or liver metastases) throughout the course, achieving sustained deep remission. As of the latest reexamination in May 2025, the progression-free survival reached 41 months, and the overall survival has not been reached yet. Conclusions: For this highly aggressive SMARCA4-deficient tumor, the sequential treatment strategy of "induction chemotherapy-immunotherapy followed by consolidative radiotherapy" enables long-term disease control, and immunotherapy maintenance also demonstrated significant value in delaying disease progression. The experience from this case could inform the diagnostic and therapeutic approach for this rare subtype of lung cancer.