Cytologic Characteristics of Thymic Adenocarcinoma with Enteric Differentiation: A Study of Four Fine-Needle Aspiration Specimens

Thymic adenocarcinoma is extremely rare. Although its histologic features have been occasionally reported, a lack of description of the cytologic features has hampered the prompt and accurate diagnosis of this condition. Herein, we describe the cytologic findings and histology of four aspiration cytology specimens of thymic adenocarcinoma. The specimens were obtained from primary tumors, metastatic lymph nodes, and pericardial effusions. All four specimens showed three-dimensional glandular clusters with a loss of polarity and nuclear overlapping. One specimen had extensive extracellular mucinous material. Three specimens contained tumor cells with intracytoplasmic vacuoles. While the specimen with extracellular mucin showed relatively mild cytologic atypia, other specimens exhibited more atypical cytologic changes: irregular nuclear membranes, a coarse chromatin pattern, and prominent nucleoli. The cytologic features were correlated with the histologic features in each case of enteric type thymic adenocarcinoma. The differential diagnosis included other thymic carcinomas, yolk sac tumors, and metastatic adenocarcinoma from the lung or colorectum.