SMARCB1 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily b, member 1) is a member of the SWI/SNF chromatin remodeling complex and regulates transcription of several genes involved in cell proliferation. Simple variants in SMARCB1 are seen in about 2% of all tumors, including about 20% of soft tissue tumors and 7% of central nervous system tumors. SMARCB1 inactivation is characteristic of atypical teratoid/rhabdoid tumors. SMARCB1 inactivation may predict response to EZH2 inhibitors.