Efficacy of Immune Checkpoint Inhibitors in SMARCA4-Deficient Thoracic Tumor

SMARCA4-deficient thoracic tumor is a novel disease entity characterized by mutations in SMARCA4 resulting in loss of its expression. They could be divided according to their phenotypes; carcinoma or sarcomatoid. It remains unclear how many patients with these SMARCA4-deficient tumors could benefit from inhibitors of programmed death 1 (PD-1) or programmed death ligand 1 (PD-L1).SMARCA4-deficient thoracic tumor cases were retrospectively identified from pathology and gene expression databases at the National Cancer Center Hospital in Japan. Clinical outcomes of patients treated with PD-1/PD-L1 inhibitors were reviewed.Eighteen patients with SMARCA4-deficient thoracic tumor [carcinoma (n = 10), sarcomatoid (n = 7), and ambiguous type (n = 1)] were identified. Of the twelve [carcinoma (n = 7), sarcomatoid (n = 5)] who had received immune checkpoint inhibitors (ICIs), 5 [carcinoma (n = 3), sarcomatoid (n = 2)] showed a partial response, all of whom had received an ICI as the first-line therapy. The overall response rate was The PD-L1 tumor proportion scores of the 5 responding patients were 100%, 80%, 5% (n = 2), and less than 1%. The median progression-free survival (PFS) of all the patients was 2.4 months [95% confidence interval (CI), 1.1 months-not achieved (NA)], while the median PFS of the 3 patients who received first-line ICIs was not reached (95% CI, 1.1 months-NA).PD-1/PD-L1 inhibitors showed promising results in the treatment of SMARCA4-deficient tumor. Further studies, especially on patient selection and combination therapy, are needed.