By whole transcriptome sequencing, these samples clustered apart from the other unclassified sarcoma samples, defining a new entity of aggressive, poor prognosis thoracic primary sarcomas of young adults: “SMARCA4-deficient thoracic sarcomas.” Comparison to the profiles other SMARCA4-deficient malignancies showed that these are distinct from lung carcinomas but related to malignant rhabdoid tumors and to small-cell carcinoma of the ovary, hypercalcemic type. The gene discussed is SMARCA4; the disease is rhabdoid tumor.