CASTLE tumor of the parotid: First documented case, literature review, and genetic analysis of the cancer

Background Carcinoma showing thymus-like elements (CASTLE) is a rare tumor that normally affects the thyroid gland and was thought to arise from either the remnants of the branchial pouch or the ectopic cervical thymic tissue. These tumors show strong immunopositivity for CD5, P63, and CD117. Most CASTLE of the thyroid gland is treated with surgery with or without adjuvant radiotherapy or chemotherapy. Method A 55-year-old woman presented with a slow-growing right parotid mass. A right total parotidectomy and ipsilateral selective neck dissection were performed and the diagnosis of CASTLE was made after confirmation with an immunohistochemistry test. She received radiotherapy postoperatively. Results Genetic sequencing showed alterations in the PPARG, BRCA2, and NOTCH1 genes. She remained disease free for >1 year after treatment. Conclusion We believe that this is the first reported case of CASTLE in the parotid gland. Clinicians should be aware of this rare entity and consider this differential diagnosis after ruling out other common parotid lesions.