Therefore, this entity is now termed SMARCA4 deficient undifferentiated tumor rather than sarcoma and must be distinguished from SMARCA4 deficient NSCLC, since SMARCA4 mutations and/or loss of BRG1 expression occur in a subset of TTF1/p40 negative tumors, accounting for ~10% of poorly differentiated lung adenocarcinomas8,9. The gene discussed is TTF1; the disease is neoplasm.