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Background. Micronodular thymic carcinoma (MTC) with lymphoid hyperplasia is believed to be the malignant counterpart of micronodular thymoma (MT) with lymphoid hyperplasia. Since MT and MTC share a similar morphology, MTC is considered a malignant form of MT; there have been a few malignant transformations from MT to MTC. We report a case of MTC with lymphoid hyperplasia. Case presentation. A 53-year-old woman presented with an incidental tumor on a chest X-ray. The resected tumor consisted of nodular epithelial nests and lymphoid tissue within a surrounding germinal center. Some epithelial nests showed apparent malignant morphology. Atypical epithelial cells with large vesicular nuclei formed nests, some of which showed comedo necrosis. These cells showed transition continuously to low-grade type B thymoma-like cells, demonstrating cord-like arrangements. Carcinomatous elements, expressed GLUT1, CD5, KIT, and BCL2; conversely, low-grade nests displayed attenuated expression of these markers. GTF2I point mutation and Langerhans/dendritic cells, which are indicators of favorable thymoma prognosis, were not detected. Due to pleural metastasis, the patient was treated with lenvatinib 27 months postoperatively. Conclusions. This is the first report of a partially low-grade, GTF2I -negative MTC. Histological and genetic findings might be predictive of tumor prognosis. [ABSTRACT FROM AUTHOR]

Crystal-storing histiocytosis (CSH) is a rare non-neoplastic histiocytic lesion with abnormal accumulation of immunoglobulin (Ig) light chain. CSH is associated with Ig overproduction by B-lymphoproliferative disorders (B-LPDs) or by persistent inflammatory diseases. Eighteen cases of pulmonary CSH have been reported. However, no case reports of tracheal CSH have been published. In this patient, we found a solitary tracheal tumor in an asymptomatic 60-year-old man on chest computed tomography scan. Histologically, the tumor comprised two different lesions. One lesion showed diffuse proliferation of spindle-shaped histiocytes with abundant eosinophilic granular cytoplasm. With immunohistochemistry, the histiocytic cells were positive for CD68, CD163 and Ig kappa light chain, and the cytoplasm was weakly positive for anaplastic lymphoma kinase (ALK) protein. Fluorescence in situ hybridization indicated no split signals for the ALK gene. Electron microscopy demonstrated many elongated or rhomboid-shaped dense crystals in the cytoplasm of histiocytes. The second lesion showed proliferation of CD20-positive small atypical lymphocytes mixed with Ig kappa chain-positive plasma cells. A diagnosis of CSH and concomitant mucosa-associated lymphoid tissue lymphoma was made. In this patient, unexpected ALK protein was detected in infiltrating histiocytes. Therefore, careful assessment of the ALK protein and gene was necessary to differentiate from other histiocytic disorders. [ABSTRACT FROM AUTHOR]