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. We report a case of SMARCA4‐UT that was successfully diagnosed via EBUS‐cryo after unsuccessful EBUS‐TBNA and EBUS‐IFB. Conventional endobronchial ultrasonography‐guided procedures cannot provide sufficient biopsy samples for the diagnosis and staging of rare mediastinal tumors. Endobronchial ultrasonography‐guided transbronchial cryobiopsy helps obtain adequate tissue samples for histological, immunohistochemical, and molecular (including next‐generation sequencing) evaluations.