SMARCB1/INI1-deficient tumour of the thorax: a differential diagnosis to be included in thoracic basaloid tumours with ambiguous differentiation and review of the literature

Loss of switch/sucrose non-fermentable (SWI/SNF)-related, matrix-associated, actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1), also known as integrase interactor 1 (INI1), has been observed in various malignancies, including malignant rhabdoid tumour, atypical teratoid/rhabdoid tumour, epithelioid sarcoma, renal medullary carcinoma, myoepithelial carcinoma, and SMARCB1-deficient sinonasal carcinoma. Recently, rare cases of primary thoracic SMARCB1/INI1-deficient tumours have been reported and reviewed. Here, we report a case of primary lung SMARCB1/INI1-deficient tumour that fits the category of “thoracic SMARCB1/INI1-deficient undifferentiated tumour”. SMARCB1/INI1 immunohistochemistry should be performed in basaloid tumours with ambiguous differentiation in primary lung malignancy for accurate diagnosis.