The most frequent SWI/SNF complex subunit alteration in thorax, lung, pleural and mediastinal neoplasms is SMARCA4. SMARCA4 - deficient undifferentiated tumors were recently recognized as a new entity in the WHO classification of thoracic tumors and are defined as malignant neoplasms with an undifferentiated or rhabdoid phenotype and deficiency of SMARCA4 (BRG1)5. Here, SMARCA4 is linked to neoplasm of mediastinum.