Carcinoma Showing Thymus-Like Differentiation (CASTLE): A Case Report and Review of the Literature

Carcinoma showing thymus-like differentiation (CASTLE) is a rare tumor occurring in the thyroid and soft tissues of the neck. Treatments and prognosis for CASTLE significantly differ from those associated with squamous cell carcinoma and anaplastic thyroid carcinoma. To date, fewer than 100 cases have been reported. Given the lack of a standardized treatment protocol and the diagnostic complexity, documenting these cases is essential. A 74-year-old male patient was admitted to the hospital due to hoarseness lasting for 1 month and thyroid nodules for over 2 weeks. The ultrasound revealed a grade 4 nodule in the left thyroid, and the needle biopsy reported the presence of glandular epithelial cells of varying sizes, some arranged in a papillary pattern, and was negative for BRAF mutation. Thyroid surgeons performed a left partial thyroidectomy and a left cervical lymph node biopsy, and the immunohistochemical staining led to a diagnosis of intrathyroid thymus carcinoma. Follow-up on his postoperative recovery shown no signs of local recurrence or distant metastasis during this period. This paper conducts a systematic review of the literature to enhance understanding, diagnosis, treatment, and prognosis of this condition. The goal was to raise clinical awareness and guide appropriate treatment strategies.