Background Micronodular thymic neoplasm with lymphoid stroma (MNT), a subtype of thymic tumor, is histopathologically characterized by micronodular thymic epithelial cell nests with lymphoid stroma. Despite the distinct histopathology of MNT, its pathogenesis remains unclear. Methods In this study, we aimed to examine a thymic tumor harboring thymic epithelial and lymphoid cells in a nonobese diabetic/severe combined immunodeficiency mouse. Results The excised tumor cells were cultured in vitro and comprised epithelial tumor cells and lymphoid cells. During a three‐dimensional cell culture, the epithelial tumor cells formed micronodular cell nests surrounded by lymphoid stroma. Notably, the lymphoid cells underwent apoptosis when they were separated from the epithelial tumor cells. Cutaneous transplantation of the cultured epithelial cells with splenocytes from BALB/c mice led to tumor formation, and these cells demonstrated a histopathology similar to that of human MNT in a nonobese diabetic/severe combined immunodeficiency mouse. Conclusion Given its overlapping features with human MNT, the transplanted tumor could serve as an experimental model of this disease.

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Thyroid sclerosing mucoepidermoid carcinoma with eosinophilia (SMECE) is a rare tumor that typically affects women with Hashimoto’s thyroiditis. The present case was a man in his late 50s who was diagnosed with Graves’ disease at the age of 10 and was given antithyroid hormone for five years. The computed tomography scan revealed a nodular lesion in the right lobe, and the lesion was cytologically suspected as papillary carcinoma. No lymph node metastases or distant metastases were found. Before total thyroidectomy, high serum anti-thyroid peroxidase (TPO) and antithyroglobulin (TG) antibody titers, with no eosinophilia were detected. In a few small areas of the tumor center, small tumor cell foci with mild to moderate atypia, displaying mucous glandular cell and squamous cell differentiation, were found. The tumor was completely replaced by prominent sclerosing fibrosis, which was accompanied by tumor cell infiltration. The tumor had invaded the adjacent parenchyma and perithyroidal fatty tissue. In addition to lymphocytes and plasma cells, a large number of eosinophils were observed within the tumor. Immunohistochemically, tumor cells were strongly positive for p63, 34βE12, and TTF-1, but weakly for PAX8. Using fluorescence in situ hybridization (FISH), no MAML2 translocation was detected. Taken together with these findings, the present tumor was diagnosed as primary thyroid sclerosing mucoepidermoid carcinoma with eosinophilia (SMECE). This case is the first to report thyroid SMECE associated with Graves’ disease. IL-5 immunostaining was performed to identify eosinophilia within the present tumor. As a result, the tumor cells were found to be positive for IL-5. The present tumor is also the first to indicate IL-5 production of SMECE.