FRI498 Paraneoplastic Hyperthyroidism In A Patient With B-hCG Secreting Gastric Carcinoma

Disclosure: F. Perreault: None. M. Tehfe: None. M. Laskine: None. L. Ste-Marie: None. R. Comtois: None. B. Nguyen: None. J. Murphy-Lavallée: None. A. Rakel: None. Introduction: Human chorionic gonadotropin (hCG) has thyrotropic activity, due to a similar structure to TSH. Increased hCG serum levels can cause hyperthyroidism secondary to TSH-receptor activation. hCG can be increased in conditions outside of pregnancy, such as gestational trophoblastic disease and other tumors. Common hCG secreting tumors are non-seminomatous germ cell tumors, including choriocarcinoma and teratoma(1). Even if gastric adenocarcinomas can secrete ß-hCG, the serum level is rarely elevated(2). Clinical Case: A 75-year-old man presented to the hospital for abdominal pain, diarrhea, and important recent weight loss. The patient was known for hypertension, dyslipidemia, type 2 diabetes, and chronic kidney disease. He had been investigated for sub-clinical hyperthyroidism one year prior (TSH 0.27 mUI/L (N 0.38-5.33), T4 14 pmol/L (N 8.0-20.0), T3 4.7 pmol/L (N 3.8-6.0), normal thyroid ultrasound and normal uptake at scintigraphy). At physical examination, the patient looked anxious, had a light lid lag, sinus tachycardia (120 BPM) and a new systolic heart murmur. The thyroid exam was normal and there was no pretibial myxedema nor exophthalmia. The blood tests showed normocytic anemia (Hb 113 g/L, N>130), low TSH (< 0.01 mUI/L), and elevated free T4 (74.1 pmol/L) and T3 (22.5 pmol/L). A work-up for hyperthyroidism revealed normal anti-TPO (4 UI/mL, N<9) and TSH receptor (1.2 UI/L, N<1.8) antibodies levels. Tc-99m thyroid scintigraphy showed homogeneous and intense uptake, with no nodule. Additionally, the abdominal CT-scan revealed multiple retroperitoneal lymphadenopathies and liver hypodensities, suspicious of neoplasia. In this context, the patient underwent gastroscopy, and a gastric antral mass was discovered. Neoplastic markers were measured and, unexpectedly, ß-hCG was strongly elevated (>1 080 800 U/L, N<2.0). Testicle ultrasound was normal. The antral mass biopsy was consistent with infiltrating gastric adenocarcinoma, with ring cells containing intracellular mucin and expressing hCG. The patient was treated with methimazole and propranolol. Free T3 and T4 initially decreased with this treatment (to 7.1 pmol/L and 46.4 pmol/L respectively), but one month later, the serum values were higher (14.9 pmol/L and 69.2 pmol/L). No follow-up was possible for this patient as he passed away before receiving treatment for cancer. Conclusion: ß-hCG induced hyperthyroidism can aggravate patients’ malignant manifestations and should be considered in cases presenting with concomitant cancer and hyperthyroidism. References: 1. Oosting SF et al. Prevalence of paraneoplastic hyperthyroidism in patients with metastatic non-seminomatous germ-cell tumors. Ann Oncol. 2010;21(1):104-8. 2. Ben Kridis W et al. Gastric signet-ring cell carcinoma with hypersecretion of β-Human chorionic gonadotropin and review of the literature. Exp Oncol. 2018;40(2): 149-51. Presentation: Friday, June 16, 2023