SMARCA1 and small cell lung carcinoma: Notably, mutations in SMARCA4 (also known as BRG1), which encodes an ATPase subunit of SWI/SNF chromatin-remodeling complexes (26), were observed in six out of eight SCLC-Y lines and found mutually exclusive with RB1 mutations (Fig. 1B; Supplementary Fig. S1A).