Supplementary Material for: Primary Squamous Cell Carcinoma of Thyroid Gland: a case report and review of the literature

Introduction:
Primary squamous cell carcinoma of the thyroid (PSCCT) is an exceptionally rare and aggressive malignancy, accounting for <1% of thyroid tumors, with a high mortality rate (≈80% within three years).

Case presentation:
This report details a case of PSCCT in a 57-year-old asymptomatic non-smoker presenting with neck discomfort. Diagnostic evaluation, including cervical ultrasound, revealed heterogeneous thyroid nodules with concerning features and associated cervical lymphadenopathy (hypoechoic nodes, calcifications, necrosis). Biopsies indicated Bethesda V (right lobe) and Bethesda II (left lobe) lesions, prompting a total thyroidectomy for suspected differentiated thyroid carcinoma in a euthyroid multinodular goiter. Histopathology confirmed well-differentiated squamous cell carcinoma (CK5/6-positive) with no surgical margin involvement. Subsequent CT, PET-CT, and targeted endoscopic evaluations excluded metastatic or secondary sources, confirming primary PSCCT. A right-sided cervical lymph node dissection was subsequently performed for radiologically suspicious lymphadenopathy, followed by postoperative radiotherapy using volumetric modulated arc therapy (VMAT). Weeks after radiotherapy, the patient developed vocal cord edema and dyspnea, most likely related to radiation-induced complications, necessitating tracheostomy

Conclusion:
PSCCT’s etiology remains debated, with the metaplastic theory (chronic inflammation driving squamous metaplasia) gaining traction. Diagnosis requires rigorous exclusion of secondary metastases via multimodal imaging and selective endoscopy. Treatment hinges on radical resection, though adjuvant therapies show limited efficacy. Despite aggressive intervention, the prognosis remains poor, often due to local invasion or airway compromise. This case underscores the diagnostic complexity, therapeutic challenges, and dismal outcomes associated with PSCCT, emphasizing the need for early detection and the exploration of novel targeted and immunotherapeutic strategies.