Carcinoma showing thymus‐like differentiation of the parotid gland: The brief report of cytomorphology and review of the literature

Here, we report an extremely rare case of carcinoma with thymus‐like differentiation (CASTLE) of the parotid gland. CASTLE is a rare malignant epithelial tumor with thymic epithelial differentiation that arises in the thyroid gland or perithyroidal soft tissue. CASTLE of salivary gland origin is rare, with only nine published case reports to date (reported as “CASTLE” or “thymic carcinoma”). It is critical to diagnose salivary gland tumors using fine needle aspiration cytology. However, this tumor is rare, and there have been few studies on its cytomorphological features. Therefore, it is important to understand the cytological diagnostic characteristics of CASTLE. Herein, we review the cytological features and diagnostic characteristics of salivary gland CASTLE. We also report the genotype results obtained using targeted exome sequencing, which we analyzed with DNA extracted from formalin‐fixed paraffin‐embedded tissue.