SAT564 Metastatic Malignant Pleural Effusion In A Patient With Remote History Of FTC

Disclosure: D.M. Lee: None. M. Gong: None. C. Czerlanis: None. A. Arif: None. R. Arceo-Mendoza: None. Introduction: Differentiated thyroid follicular epithelial-derived cancers include Papillary (PTC) and Follicular Thyroid Cancer (FTC). FTC is less common, accounting for only 5-15% of all thyroid cancers. It is more common in older patients and spreads via hematogenous route, with distant metastases in 10-15% of patients, commonly in the lungs and bone. We describe an unusual case of a patient with a remote history of FTC who presents with recurrence more than 50 years later in the form of a malignant pleural effusion. Clinical Case: A 79/M with a remote history of FTC that was diagnosed in the 1960s presents with one week of L sided pleuritic chest pain and dyspnea. CXR on admission showed opacification of the L hemidiaphragm. A chest CT confirmed the L sided pleural effusion. Thyroid US showed surgically absent thyroid and a 1.1cm solid nodule in the L surgical bed. PET/CT demonstrated hypermetabolic rim of L pleural effusion with no uptake in the neck. Thoracentesis was done which showed exudative pleural fluid concerning for malignancy. Immunohistochemical stains were positive for TTF-1 and thyroglobulin, consistent with metastatic thyroid cancer. He also underwent L supraclavicular lymph node FNA with findings suspicious for metastatic thyroid cancer with follicular features, with NO nuclear features of PTC. On further history, the patient reports having radiation therapy for acne around age 17 and was then diagnosed with FTC in his 20s. He underwent total thyroidectomy and RAI treatment. He recalls being told that he had a few weeks to live, and an “experimental treatment” was offered at the time, which we suspect was cobalt radiation. The patient unfortunately was eventually lost to endocrine follow up but denies any known recurrence prior to this admission. Upon discharge, an I-123 WBS was performed showing multiple foci in the R neck. Uptake is also noted in bilateral lung base, greater on the left. He was treated with 250 mCi I-131. He is currently doing well overall, asymptomatic, and with stable surveillance imaging. He is on levothyroxine suppression therapy with Tg level on a downward trend. Clinical Lesson/Conclusion: Involvement of pleural fluid by metastatic thyroid cancer though reported, is relatively rare, accounting for only less than 1% in all the patients with malignant pleural effusion. To our knowledge, there are no reported cases of malignant pleural effusions from metastatic FTC presenting remotely so many years after the initial diagnosis. The diagnosis of metastatic thyroid cancer in pleural fluid can be challenging and knowledge of the clinical context, even with remote history dating back 50 years ago just like in our case, and supporting immunohistochemical stains is essential for making the right diagnosis. Presentation Date: Saturday, June 17, 2023