SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A (SMARCA4)-deficient undifferentiated tumors are high-grade neoplasms defined by the loss of SMARCA4, also known as Brahma-related gene 1 (BRG1), a key catalytic subunit of the SWI/SNF chromatin remodeling complex [1]. The gene discussed is SMARCA4; the disease is neoplasm.