Thoracic SMARCA4-deficient undifferentiated tumor diagnosed by transbronchial mediastinal cryobiopsy: A case report

Thoracic SMARCA4-deficient undifferentiated tumors (SMARCA4-UT) have a poor prognosis and are often diagnosed at an inoperable advanced stage. Herein, we report a case of SMARCA4-UT diagnosed by endobronchial ultrasound-guided transbronchial cryobiopsy (EBUS-cryo). The patient was a 42-year-old man with a history of smoking. Chest computed tomography revealed a right upper lobe nodule and an enlarged #11s lymph node. Core tissues could not be obtained by EBUS-guided transbronchial needle aspiration (EBUS-TBNA) for diagnosis and mediastinal staging; hence, EBUS-guided intranodal forceps biopsy (EBUS-IFB) was performed. However, a detailed diagnosis beyond poorly differentiated carcinoma could not be obtained. Subsequent EBUS-cryo provided sufficient specimens for immunohistochemical and molecular evaluation and SMARCA4-UT was definitively diagnosed. Thus, EBUS-cryo could be of additional diagnostic value for uncommon tumors, such as SMARCA4-UT, conjointly with EBUS-IFB as well as EBUS-TBNA.