https://www.liebertpub.com/doi/full/10.1089/ve.2021.0032

Abstract

Introduction: Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare malignant tumor of the thyroid gland. It is believed to arise from thymic tissue or branchial pouch remnants showing thymic or branchial pouch differentiation. Besides its reported slow growing rate, its diagnostic importance lies in its representative metastatic potential. Approximately 50 cases have been reported around the globe and only 4 reported in Latin America. Herein, we report the first case of SETTLE from Ecuador.1

Description of Case: A 24-year-old man with no significant medical history and no risk factors for thyroid cancer was admitted to the head and neck department complaining of a rapidly growing neck mass. Physical examination revealed a 4.2 × 5.4 cm hard, painless, and immobile mass in the anterior neck. Complementary ultrasonography (US) showed a 4.1 × 3.2 cm left lobe mass with solid and cystic components. Fine-needle aspiration biopsy of the nodule was compatible with undifferentiated carcinoma with spindle cells Bethesda VI. Differential diagnoses at this time were anaplastic thyroid cancer, malignant teratoma, and ectopic thymoma. Before operating on the patient, a whole-body CT was ordered.

It confirmed a thyroid mass raising from the left lobe of 5.3 × 4.3 × 4.3 cm comprising the trachea with some cervical lymph nodes up to 0.97 cm nodes in levels 2B, 3, 4, and 7 bilaterally, and level 1 only in the left compartment. There was no evidence of distant metastasis. In light of rapidly progressive obstructive symptoms, the patient underwent R0 total thyroidectomy using intraoperative recurrent laryngeal nerve monitoring, with central (2/6 positive) and left lateral (14/14 negative) neck lymph node dissection. The dissection was extended to the thymus. The patient was uneventfully discharged on postoperative day 1.

No radiotherapy was planned. To confirm the suspected SETTLE, histopathology and immunohistochemistry were performed (positive for cytokeratin, CD99, TTF-1, and smooth muscle actin; negative for cytokeratin 9, thyroglobulin, and PAX8). The analysis confirmed the diagnosis of SETTLE in the left lobe of this patient's thyroid. We followed the patient at 1, 3, and 6 postoperative months and subsequently every 6 months to make sure to find metastases or recurrence in a timely manner. Recently the patient was seen at his 6-month follow-up, and there were no signs or symptoms of recurrence or metastasis.

Discussion: To the best of our knowledge, this is the first Ecuadorian and the fifth Latin American patient being diagnosed with SETTLE. Although some studies have reported late metastasis, with the cervical lymph nodes, lungs, and mediastinum being the most frequently involved sites,2 the clinical course of SETTLE is quite unpredictable. Therefore, a strict long-term follow-up (as in this case) must be pursued even in patients with an apparent cure, as there is not enough evidence about SETTLE and its natural history. Our patient had cervical lymph node metastases, however, a correlation between recurrence or mortality risk and tumor size or lymph node metastasis at diagnosis has not been established.3

Regular physical examination should be considered in all visits complemented with neck US, and neck and chest CT performed every 6 months in the first 2 years and then annually even in the absence of specific symptoms.3,4 Although SETTLE is a rare neoplasm of the thyroid, physicians should include this entity as a differential diagnosis of other head and neck neoplasms. Finally, surgical resection is the mainstay therapy for SETTLE including resection of the primary and oligometastatic disease and there is no role for adjuvant chemotherapy or radiotherapy.5

The authors declare that no competing financial interests exist or any conflicts of interest or obligations resulting from this article. The case was obtained from the Head and Neck Department, ITECC (Instituto de la Tiroides y Enfermedades de Cabeza y Cuello), Quito, Ecuador.

The patients provided informed written consent to disseminate this article.

Runtime of video: 7 mins 8 secs

This article was presented at the 90th Annual Meeting of the American Thyroid Association®, September 30 to October 3, 2021.