A case of poorly differentiated thyroid carcinoma harboring an SMARCB1 mutation

SWItch/sucrose non-fermentable (SWI/SNF) chromatin-remodeling complexes regulate nucleosome positioning. Its involvement has been suggested in anaplastic thyroid carcinoma and poorly differentiated thyroid carcinoma. We herein report an extremely rare case of poorly differentiated thyroid carcinoma harboring a mutation in SMARCB1, a subunit of the SWI/SNF complex. The patient was a 75‑year‑old woman with bilateral thyroid nodules who had been followed up for 27 years, with cytology classified as Bethesda II. The nodule enlarged rapidly to 7 cm, and computed tomography suggested airway invasion and multiple pulmonary nodules. An open biopsy of the thyroid mass was performed, and the lesion was diagnosed as poorly differentiated thyroid carcinoma. Lenvatinib therapy was initiated at the previous hospital, resulting in tumor shrinkage, and total thyroidectomy was performed 62 days after the initiation of treatment. Five months later, the patient was referred to our hospital for surgical management of pulmonary lesions. Left basal segmentectomy was performed, and histopathological examination confirmed metastasis from poorly differentiated thyroid carcinoma. Lung metastatic tissue was submitted to GenMineTOP, and an SMARCB1 mutation was detected. At the time of this report, 2 years and 7 months had passed since the initial surgery. Lenvatinib therapy was continued, and the disease remained stable. We report a case of poorly differentiated thyroid carcinoma with an SMARCB1 mutation. The accumulation of similar cases and additional immunohistochemical evaluations of past specimens may contribute to the development of targeted therapeutic strategies.