Abstract
Disclosure: I.E. Hernandez Castro: None. E.J. Sola Sanchez: None. M.M. Mangual Garcia: None. Head and neck squamous cell carcinoma (SCC) have predilection for cervical lymph node metastasis, with the lungs, mediastinum, bone, and central nervous system being the most common metastatic sites. Thyroid metastases from laryngeal SCC are rare. Differentiating primary thyroid malignancies from metastases is crucial for treatment and prognosis. We present a case of SCC metastases to the thyroid, which could have been mistaken for a poorly differentiated thyroid carcinoma. A 75-year-old male, former smoker, with a 55 pack-years history that quit 20 years ago, and laryngeal carcinoma (diagnosed in 2022) was treated with radiotherapy and chemotherapy, followed by total salvage laryngectomy and subtotal thyroidectomy in 2024. The patient was referred to our endocrinology clinic at San Juan City Hospital for uncontrolled hypothyroidism (TSH 43mIU/L), for which levothyroxine therapy was initiated. Preoperative imaging did not reveal any thyroid lesions. A post-surgical thyroid ultrasound (2024) revealed a solid, hypoechoic left thyroid nodule of 1.8 x 1.3 x 1.7 cm measurements without calcifications or other suspicious features. Fine-needle aspiration cytology (FNA) reported Bethesda VI: malignant and poorly differentiated carcinoma, with findings highly suggestive of SCC. Immunohistochemistry (IP25-17) was negative for TTF-1, favoring a non-thyroidal origin. A PET CT scan is pending to evaluate for additional metastatic disease and guide therapeutic management. Thyroid metastases from SCC are rare, with laryngeal cancer as an unusual primary source. Most secondary thyroid malignancies arise from renal, lung, or breast cancer, making this case a unique diagnostic challenge. The absence of TTF-1 positivity supported metastatic SCC rather than primary thyroid malignancy. Given the patient’s history and pathological findings, the diagnosis of SC metastasis to the thyroid was established. Management options include surgical resection, systemic therapy, and palliative care, depending on metastatic burden. This case highlights the importance of distinguishing metastatic SCC from primary thyroid malignancies, as treatment strategies differ significantly. Endocrinologists should maintain a high index of suspicion for thyroid metastases in patients with a history of head and neck malignancies, particularly laryngeal SCC. No specific sonographic features have been described for metastatic SCC to the thyroid, and this pathology could also be mistaken for benign thyroid adenomas, further complicating the diagnosis. Further studies are needed to establish optimal management strategies for these rare cases. Presentation: Sunday, July 13, 2025