CD5 and carcinoma: Definite diagnosis is based on an immunohistochemical examination, as this carcinoma shows positive CD5 immunoreactivity when compared to other aggressive thyroid carcinomas.<h4>Case presentation</h4>The main focus of this study is to outline a rare case of CASTLE compressing the trachea in a 50-year-old female patient who was initially diagnosed with undifferentiated thyroid carcinoma, for which she underwent unsuccessful surgery, as well as postoperative radiotherapy and chemotherapy.