The patient, a 28-year-old man with a 3-month-old mass in the neck was referred to our department. The mass, located on the left thyroid lobe, was elastic, hard, showed limited mobility, and measured approximately 30 × 20 mm. There was no remarkable tenderness over the mass.\nBlood examination results were normal, including levels of thyroid-stimulating hormone, free thyroid hormone, and thyroglobulin (Table ). Ultrasonography revealed a hypoechoic solid mass in the lower pole of the left thyroid lobe with a poorly marginated heterogeneous pattern (Fig. ). Computed tomography revealed a heterogenic tumor in the left thyroid lobe (Fig. ). 18F-fluorodeoxyglucose (18F-FDG) accumulated in the thyroid tumor on positron-emission tomography. The standardized uptake value of 18F-FDG was 5.29 (Fig. ). Fine-needle aspiration cytology (FNAC) showed a number of lymphoid cells without atypia that were similar to those seen in malignant lymphoma of the thyroid (Fig. ).\nAs we diagnosed a highly malignant thyroid cancer (cT2N0M0), we performed a left hemithyroidectomy with central neck dissection (ND). Histopathological findings showed that the tumor was composed of irregular insular nests of neoplastic cells and had an expansive growth pattern in the thyroid (Fig. ). The carcinoma cells had round nuclei or polymorphonuclei with well-defined nucleoli and ill-defined cell borders (Fig. ). Immunohistochemical studies showed that the tumor was partially positive for CD5, positive for Ki-67 (approx. 30%), and negative for CD20, calcitonin, and thyroglobulin (Fig. ). Based on these histopathological findings, the tumor was finally diagnosed as CASTLE. There were no signs of recurrence without additional treatment after 10 years of follow-up.
Patient 1 was a 61-year-old female who presented with a 5-cm anterior neck mass with retrosternal extension. She was surgically treated with a right thyroid lobectomy at another institution. The lesion was interpreted to be a poorly differentiated papillary thyroid cancer. Postoperative treatment consisted of sequential and combined chemoradiotherapy. Local recurrence in the region of the right thyroid occurred 20 months later, and radiotherapy was performed to relieve symptoms. Six years later, the patient had local recurrence again and was referred to our institution for further treatment. After curative wide local excision and central neck dissection, postoperative radiotherapy was given to the thyroid bed and bilateral cervical lymph node areas (55 Gy/16 fractions). Histological re-evaluation of the recurrent tumor specimens revealed CASTLE (pT4bN1M0). A third local recurrence was diagnosed 1 year later, and concurrent chemotherapy (paclitaxel 210 mg/m2 and cisplatin 40 mg/m2) and radiotherapy (50.4 Gy /28 fractions) were applied. The patient died from acute respiratory distress 1 month after the initiation of treatment.