Micronodular Thymic Carcinoma With Lymphoid Hyperplasia: A Case Report and Next Generation Sequencing Analysis With its Benign Counterpart Multinodular Thymoma With Lymphoid Stroma

Micronodular thymic carcinoma with lymphoid hyperplasia (MNC) is an extremely rare tumor. Fewer than 30 histologically proven examples of MNC have been described in the English literature. A 64-year-old man with a history of colon cancer presented with an anterior mediastinal mass on follow-up examination. Surgical excision was performed. Macroscopically, the mass (3.0 x 2.7 cm) was relatively well-demarcated and surrounded by fat. The cut surface was tan yellow and solid. Microscopically, it showed multiple small tumor islands composed of frankly malignant epithelial cells with pleomorphism and increased mitotic activity. They were arranged in a micronodular growth pattern and surrounded by lymphoid stroma composed of CD3-positive small T-lymphocytes and CD20-positive B-lymphocytes, highlighting numerous lymphoid follicles with germinal centers. A diagnosis of MNC was made. We also report comparatively analyzed genetic alterations in MNC and its benign counterpart, micronodular thymoma with lymphoid stroma (MNT) by next-generation sequencing. For therapeutic interventions, awareness of this rare disease is essential in order not to confuse this tumor with MNT or metastatic carcinoma in mediastinal lymph nodes. And further clinical concordance studies with genomic analysis in the larger number of MNCs should be followed.