SUN-324 Uncommon Metastasis: Squamous Cell Lung Cancer Presenting in the Thyroid Gland

Abstract Disclosure: D. Kaul: None. A.P. Calimag: None. T. Yasmeen: None. INTRODUCTION: The thyroid is an uncommon site for metastasis, with renal cell (48.1%) and colorectal (10.4%) carcinomas being the most frequent sources. Lung (8.3%) and breast (7.8%) cancers can also metastasize here. We present a rare case of squamous cell carcinoma (SCC) of the lung metastasizing to the thyroid gland. CLINICAL CASE: A 70-year-old female presented with shortness of breath, cough, and dysphagia for one week. Her medical history included stage 1 SCC, treated with stereotactic radiation, and nontoxic multinodular goiter. Computed tomography of the chest showed a high-grade substernal goiter compressing the trachea. Positron emission tomography-computed tomography (PET-CT) showed hypermetabolic thyroid nodules and no other sites of focal fluorodeoxyglucose (FDG) uptake in the body. Ultrasound-guided fine needle aspiration of a left thyroid nodule suggested poorly differentiated carcinoma with squamous differentiation. She underwent a left partial thyroidectomy for compressive symptoms, and pathology confirmed metastatic squamous cell carcinoma (SCC) with positive p40 staining. CONCLUSION: We report a rare case of metastatic SCC of the lung in the thyroid gland. Thyroid metastasis is uncommon due to its rich vascular supply and high iodine content. Renal and colorectal cancers are the most common primary sources, with SCC of the lung being rare. Ultrasound findings include hypoechoic nodules with intranodular angiogenesis. PET-CT is recommended for monitoring patients with malignancies, as it can detect metastatic sites promptly. Immunohistochemistry (IHC), including squamous marker p40 for SCC, is crucial for diagnosis. While thyroid metastases were once considered indicative of widespread disease, Chung et al. showed that 40.3% occur in isolation. Treatment includes surgery, radiotherapy, and chemotherapy, with surgery recommended for isolated metastasis, as in this case. This case highlights the importance of maintaining a high index of suspicion for metastatic squamous cell carcinoma in the thyroid in patients with a history of extrathyroidal malignancies. It also emphasizes the vital role of a definitive pathological diagnosis in guiding appropriate clinical management. Early recognition and surgery in appropriate cases are key to managing thyroid metastasis and preventing complications. Presentation: Sunday, July 13, 2025