2026 年 21 巻 3 号 p. 336-342
Background: Sclerosing mucoepidermoid carcinoma with eosinophilia (SMECE) is an extremely rare thyroid tumor that frequently arises in association with chronic lymphocytic thyroiditis. We report a rare case of SMECE and mucosa-associated lymphoid tissue (MALT) lymphoma diagnosed simultaneously in the same thyroid gland.
Case report: A man in his 60s with serological findings suggestive of Hashimoto’s thyroiditis was referred to our hospital after a thyroid nodule was incidentally detected on carotid ultrasonography. Fine-needle aspiration cytology revealed clusters of intermediate-type epithelial cells with an eosinophil-rich inflammatory background. Left thyroid lobectomy was performed to establish a diagnosis.
Results: Histologically, the tumor showed dense stromal sclerosis with nests of squamoid cells, intermediate-type cells, and mucin-producing cells, accompanied by marked eosinophilic infiltration. Immunohistochemistry demonstrated positivity for CK5/6, p63, and CK19 and negativity for thyroglobulin and TTF-1. Fluorescence in situ hybridization analysis revealed no MAML2 gene rearrangement. Chronic lymphocytic thyroiditis was present in the surrounding thyroid tissue, along with extranodal marginal zone lymphoma of the MALT.
Conclusion: This case suggests that chronic inflammatory conditions associated with Hashimoto’s thyroiditis may have contributed to the tumorigenesis of both the epithelial and lymphoid components. Recognizing this rare coexistence is important for accurate pathological diagnosis.
