MON-340 Choriocarcinoma-Associated Thyrotoxicosis: Unveiling a Rare Paraneoplastic Syndrome

Abstract Disclosure: O.Z. Syed: None. O. Faour: None. M. Kinaan: None. Introduction: Choriocarcinoma is a rare gynecological malignancy arising from trophoblastic epithelium. Human chorionic gonadotropin (hCG)-induced thyrotoxicosis is a rare paraneoplastic phenomenon attributed to the structural similarity between hCG and thyroid-stimulating hormone (TSH), allowing hCG to activate the TSH receptor at high levels. We report a case of symptomatic hyperthyroidism related to metastatic choriocarcinoma in a young female patient.Case PresentationA 24-year-old female presented with symptomatic anemia and abnormal uterine bleeding. Hysteroscopy with dilation and curettage revealed a suburethral mass, and hemorrhagic complications required uterine artery embolization. Pathology confirmed choriocarcinoma with lung metastases. Initial labs indicated suppressed TSH (0.08 µIU/mL), elevated free T4 (2.93 ng/dL), and beta-hCG >200,000 mIU/mL. Thyroid antibodies, including TSI and TPO, were negative, and thyroid ultrasound was normal with no nodules. She was diagnosed with hCG-induced thyrotoxicosis and managed symptomatically and was started on methimazole 10 mg daily, with management focused on the underlying choriocarcinoma.DiscussionThis case underscores the complex interplay between choriocarcinoma and thyroid dysfunction. hCG’s alpha subunit homology to TSH underpins its thyrotropic effects, typically manifesting when hCG levels exceed 200,000 mIU/mL. Thyrotoxicosis symptoms—including tachycardia, weight loss, and heat intolerance—may mimic metastatic disease, complicating diagnosis. Previous reports highlight varied presentations, from subclinical hyperthyroidism to thyroid storm, as seen in severe cases The primary treatment for hCG-induced thyrotoxicosis is chemotherapy, targeting the underlying malignancy. Chemotherapy can initially exacerbate hCG levels due to tumor lysis, increasing the risk of thyroid storm. Adjunctive antithyroid medications, such as methimazole, are reserved for significant, prolonged hyperthyroidism. Comparable cases of metastatic choriocarcinoma in men and women further illustrate this phenomenon. This case affirms the importance of multidisciplinary care, encompassing endocrinology, oncology, and critical care teams.ConclusionhCG-induced thyrotoxicosis is a rare but significant complication of metastatic choriocarcinoma. Prompt recognition and treatment are critical to improving outcomes. While chemotherapy remains the cornerstone of management, symptomatic control with beta-blockers and antithyroid medications may be necessary. Monitoring thyroid function during chemotherapy is essential to mitigate complications, including thyroid storm. Presentation: Monday, July 14, 2025