Hyper‐progressive disease after immune checkpoint inhibitor in SMARCA4‐deficient small‐cell lung carcinoma

SMARCA4 (switch/sucrose non‐fermentable‐related, matrix‐associated, actin‐dependent regulator of chromatin, subfamily A, member 4)‐deficient thoracic tumours have shown poor prognosis in clinical settings. Although the optimal treatment for SMARCA4‐deficient thoracic tumours remains unclear, existing studies indicate a favourable response of these tumours to immune checkpoint inhibitors (ICIs). However, there are no reports of fatality in SMARCA4‐deficient small‐cell lung carcinoma (SCLC) with hyper‐progressive disease (HPD) upon treatment with ICIs. Herein, we report a patient with SMARCA4‐deficient SCLC who had HPD after the first ICI treatment. A 35‐year‐old man was treated with nivolumab, subsequent to cytotoxic chemotherapy. A week after nivolumab initiation, chest computed tomography revealed marked increase in pleural effusion in the right lung and chest wall dissemination of the tumour, which concur with the definition of HPD. This is the first study to report the occurrence of HPD after treatment with ICIs in a patient with SMARCA4‐deficient SCLC. Analysis of additional data is necessary to determine the optimal treatment for these patients.