There is uncertainty as to whether the histogenesis of SD-TS represents undifferentiated/dedifferentiated carcinomas or de novo genesis. Furthermore, SMARCA4/BRG1 protein–deficient thoracic sarcoma (SD-TS) is also recognized more frequently, primarily due to rising awareness of its existence. SMARCA4-inactivating mutations and consequent loss of functional SMARCA4/BRG1 protein are observed in many tumor types and are observed in 8.43% of non–small cell lung cancers (NSCLC).
