SMARCA4 and carcinoma: Finally, inactivation of SMARCA4 and subsequent loss of SMARCA4 is also characteristic of rare undifferentiated tumors of the thoracic cavity that were initially described as ‘SMARCA4-deficient thoracic sarcoma,’ though it appears that a significant number of these represent smoking-associated thoracic undifferentiated/de-differentiated carcinomas [67].