SAT531 Thyroid Metastasis From Non-small Cell Lung Cancer: An Unusual Case Presentation

Disclosure: E.Y. Ibrahim: None. I. Guillen Alvarez: None. I. Hulinsky: None. D. Regelmann: None. C. Janowiecki: None. Background: Cases of thyroid tumors metastasizing from the lungs are rare, and their diagnosis is often challenging and can be mistaken for primary thyroid tumors or subacute thyroiditis. Thyroid function tests are typically normal and not helpful in establishing the diagnosis. Ultrasonography commonly shows focal or diffuse hypoechoic lesions. Correspondingly, heterogeneous hypodense areas with mild contrast enhancement are seen on CT scans. Clinical Case: Our patient is a 61-year-old male with a history of diabetes mellitus and 40 years tobacco use, who presented with a 1-week history of right-sided weakness and 3-weeks of dry cough. The weakness of his leg progressed to the point he could not ambulate. Initially, he was evaluated for a stroke and underwent CT imaging showing extensive lesions of the bilateral frontal, temporal, and parietal lobes. These findings were suspicious, and confirmed by MRI, to reflect multifocal metastatic lesions with vasogenic edema. Initial physical examination revealed a palpable thyroid nodule in the right lobe with bilateral cervical lymphadenopathy. CT of the neck demonstrated lymphadenopathy as well as multiple bilateral hypoechoic thyroid nodules, the largest of which measured 0.8 cm in the right thyroid lobe. TSH was 0.34 (0.48-4.17mU/L) with Free T4 at 1.39 (0.8-1.90ng/dL). The patient had denied symptoms of heat intolerance, tremor, or palpitations. A CT chest with contrast found a 3.5 cm cavitary lesion in the right upper lobe concerning for a primary lung neoplasm, as well as multiple bilateral lung nodules, mediastinal and hilar lymphadenopathy, and bilateral adrenal masses. Subsequent ultrasound-guided biopsy of the thyroid tumor revealed histologic features of a poorly differentiated non-small cell carcinoma, with features of a primary lung origin. These features were also present on a concurrent fine needle biopsy of an enlarged cervical lymph node. Immunohistochemistry staining showed the tumor was highly expressive for PDL1, focally positive for p40, pancytokeratin AE1/AE3, and negative for TTF-1 and thyroglobulinDue to the vasogenic cerebral edema, he was given dexamethasone with good response, and his weakness improved to the point that patient was able to ambulate. Treatment also included radiation therapy with subsequent pembrolizumab upon completion of radiotherapy. Conclusion: Several thyroid lesions representing metastases may go unnoticed because the physician’s attention toward lesions at other, more common sites, and detailed thyroid examination can be commonly overlooked. Patients with newly diagnosed malignancies should also be screened for thyroid involvement, including detailed physical, radiographic, and histologic examination of pathologic findings. Presentation Date: Saturday, June 17, 2023