A Case of Micronodular Thymic Carcinoma with Lymphoid Stroma

Kadomatsu Yuka, Nakashima Kiyoshi, Ueno Harushi, Okasaka Toshiki, Mori Shoichi

doi:10.2482/haigan.55.59

Background. We herein report a case of micronodular thymic carcinoma with lymphoid stroma. Case. The patient was a 45-year-old woman who was being followed up for an anterior mediastinal nodule, which had increased in size from 14 mm to 18 mm over four years. The tumor showed no accumulation on a positron emission tomography scan. With a suspected diagnosis of thymoma, video-assisted partial thymectomy was performed. The tumor was yellowish-white and histologically composed of epithelial tumor cells arranged in a micronodular growth pattern. The tumor also displayed florid lymphoid hyperplasia with lymph follicles in the stroma. The histological findings revealed a superficial resemblance to micronodular thymoma with lymphoid stroma. The tumor cells, however, displayed large hyperchromatic nuclei, prominent nucleoli and anisokaryosis and were positive for CD5, bcl-2, c-kit, CK5/6 and p40. The lymphoid stroma was mainly composed of CD20-positive B-lymphocytes, and the germinal center was negative for the bcl-2 expression. The lymphocytes inside the tumor were negative for TdT. We therefore considered the lymphoid stroma to be reactive follicular hyperplasia. Overall, we recognized the tumor to be micronodular thymic carcinoma. Conclusions. To our knowledge, cases of micronodular thymic carcinoma with lymphoid stroma have not been previously reported in our country and this lesion has not been addressed by the General Rules for the Study of Mediastinal Tumors. This case report raises awareness regarding the possibility of micronodular thymic carcinoma with lymphoid stroma.

A Case of Micronodular Thymic Carcinoma with Lymphoid Stroma

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