Micronodular thymic carcinoma with lymphoid hyperplasia: a clinicopathological and immunohistochemical study of five cases

Abstract

Five cases of an unusual variant of thymic carcinoma are described, which represent the counterpart of the socalled micronodular thymoma with lymphoid hyperplasia. The patients were three men and two women aged 42-78 years (mean 64 years). Three patients were asymptomatic and the tumors were found incidentally on chest radiographs performed for unrelated reasons. Two patients complained of dyspnea, chest pain and shortness of breath prompting further investigations. The tumors ranged in size from 3.2 to 10.0 cm and were described as infiltrative masses often invading adjacent structures. Prominent cystic changes were not identified. Histologically, the neoplasms were composed of epithelial tumor cells arranged in a micronodular growth pattern set in a stroma showing florid lymphoid hyperplasia. Contrary to micronodular thymoma, the epithelial cell component of the present cases showed unequivocal signs of malignancy characterized by cytological atypia and increased mitotic activity. Immunohistochemical studies showed the lymphoid component to be of mixed B-and T-cell lineage. None of the patients had a history of myasthenia gravis or other autoimmune disorder. Follow-up revealed that 4 patients were alive and well 3-26 months after diagnosis while 1 patient was dead of disease 21 months after diagnosis. The tumors in this series represent a distinct subtype of thymic carcinoma histologically strongly resembling micronodular thymoma with lymphoid hyperplasia. Awareness of this type of thymic carcinoma is important in order not to dismiss this tumor for a neoplasm of lower-grade malignancy.

Micronodular thymic neoplasms: case series and literature review with emphasis on the spectrum of differentiation

“…Cases of micronodular thymic carcinoma with lymphoid hyperplasia 1,2 display a benign micronodular component as well as a carcinomatous component. These two constituents are most often well demarcated from each other; only rarely a transition between these two is noted (in one case of the original series 2 ). The benign micronodular component is morphologically similar to micronodular thymoma with lymphoid B-cell hyperplasia, 1,2 but the micronodules often coalesce to form more solid and irregular areas, and exhibit variable admixture of spindle and polygonal cells with mild to moderate atypia rather than solely bland spindle cells.…”

“…[3][4][5][6][7][8][9] Micronodular thymic carcinoma with lymphoid hyperplasia was more recently described as the malignant counterpart of micronodular thymoma with lymphoid B-cell hyperplasia. 2 It has clinical and demographic presentations similar to those of micronodular thymoma with lymphoid B-cell hyperplasia. Cases of micronodular thymic carcinoma with lymphoid hyperplasia 1,2 display a benign micronodular component as well as a carcinomatous component.…”

“…A conspicuous B-cell lymphoid population is rarely seen in thymomas, and lymphoid aggregates with germinal centers are only seen in a minority of thymic neoplasms. 1,2 This minor group of tumors is herein referred to as micronodular thymic neoplasms with follicular lymphoid hyperplasia, and includes micronodular thymomas with lymphoid B-cell hyperplasia, and micronodular carcinomas with lymphoid hyperplasia. In addition to the abundant lymphoid stroma with prominent follicular lymphoid hyperplasia, 1,2 these tumors are particularly characterized by a micronodular arrangement of the epithelial tumor cells as their name implies.…”

“…The benign micronodular component is morphologically similar to micronodular thymoma with lymphoid B-cell hyperplasia, 1,2 but the micronodules often coalesce to form more solid and irregular areas, and exhibit variable admixture of spindle and polygonal cells with mild to moderate atypia rather than solely bland spindle cells. 2,3 The malignant component consists of squamous cell carcinoma, spindle cell carcinoma and/or lymphoepithelioma-like carcinoma. [1][2][3] The main feature of distinction between micronodular thymoma with lymphoid B-cell hyperplasia and micronodular thymic carcinoma with lymphoid hyperplasia is the presence of areas of 'frankly' malignant component in micronodular thymic carcinoma with lymphoid hyperplasia.…”

“…2,3 The malignant component consists of squamous cell carcinoma, spindle cell carcinoma and/or lymphoepithelioma-like carcinoma. [1][2][3] The main feature of distinction between micronodular thymoma with lymphoid B-cell hyperplasia and micronodular thymic carcinoma with lymphoid hyperplasia is the presence of areas of 'frankly' malignant component in micronodular thymic carcinoma with lymphoid hyperplasia. 2 Nevertheless, the concept of morphologic spectrum of micronodular thymic proliferations, varying from benign micronodular thymoma with lymphoid B-cell hyperplasia, to micronodular thymic carcinoma with lymphoid hyperplasia, was first proposed in 2000 by Tateyama et al 3 The 11 cases in this series were divided based on morphology and immunohistochemistry, into four groups, with the group 1 showing bland spindle epithelial cells; group 2, an admixture of spindle and polygonal epithelial cells; group 3, predominance of polygonal epithelial cells with mild to moderate cytological atypia, and group 4 representing overt carcinoma (lymphoepitheliomalike carcinoma component in two cases, in addition to keratinizing squamous cell carcinoma in one of them).…”