SMARCB‐1 deficient squamous cell carcinoma of a mediastinal cyst

SMARCB1‐deficiency has been found in a variety of tumors. Here, we report a SMARCB1‐deficient squamous cell carcinoma of a mediastinal cyst. A 53‐year‐old man was diagnosed with a cyst of the pericardial region in his twenties. As a symptom at this time, he complained of severe pain and dyspnea in the right chest. Following investigation using imaging and histological examination of the biopsy specimen, he was diagnosed with a SMARCB1 deficient malignant neoplasm. As tumor cells showed positive immunostaining for p40 and CK5/6, the immunophenotype of the tumor was consistent with squamous cell carcinoma (SCC). The patient died six months after initial presentation. The autopsy showed the most part of the tumor with anaplastic cytomorphology, loss of SMARCB1, diffusely positive immunostaining for pancytokeratin, and negative immunostaining for p40 and CK5/6. To our knowledge, this is the first report of SMARCB1‐deficient SCC of mediastinal cyst.