MON-756 Synchronous Endocrine Neoplasia

Abstract Disclosure: H. Tovar Cortes: None. P.D. Nieto-Zambrano: None. N.A. Amador Ovalle: None. P. Sepulveda Yañez: None. J. Navarrete: None. Authors: Henry Tovar Cortes¹, Paula Daniela Nieto-Zambrano², Nelson Andrés Amador Ovalle², Jhon Freddy Navarrete³, Pedro Sepúlveda Yáñez⁴ Introduction: Parathyroid carcinoma (PC) represents 0.005% of all malignant neoplasms (1,2). No gender predominance has been demonstrated, and it has a mean age of presentation is between 45 and 59 years (3). Both parathyroid adenoma and PC present with hyperfunction of the affected gland in 90% of cases. A 69-year-old female patient under outpatient follow-up by endocrinology for incidental finding of primary hyperparathyroidism (PTH levels 871pg/ml) was admitted to the emergency department, referred from outpatient consultation due to serum calcium of 18 mg/dL. Upon review of systems, she reported weight loss of 3 kg over 11 months , she was asymptomatic at the time of admission. On clinical assessment, vital signs were within normal range; neck examination revealed no adenopathies, masses, or irregularities in the thyroid gland. Laboratory results are documented , showing severe hypercalcemia without renal function impairment, with a 21-fold elevation above the upper limit of normal for PTH. Given these results, primary hyperparathyroidism was considered. Neck ultrasound documented no CT scan abnormalities; however, the Parathyroid Scintigraphy (99m Tc) Sestamibi showed abnormal uptake in the right thyroid lobe over the lower portion, which was present from 5 minutes to 2 hours after radiotracer injection, consistent with parathyroid tumor. The tomographic image provided better localization of the findings, offering greater spatial orientation without describing lesions in the mediastinum. In joint assessment by head and neck surgery, the patient underwent total thyroidectomy + right uniglandular parathyroidectomy + central neck dissection. Postoperatively, she had favorable evolution without alterations in calcium control with pharmacological management, so medical discharge was indicated. The pathology study reported findings compatible with well-differentiated infiltrating parathyroid carcinoma (2.6x1.7 cm) of the right lobe, unifocal, without evident angioinvasion or lymphatic invasion. Additionally, it described multifocal papillary thyroid carcinoma (larger than 1 mm) of classic and follicular . Discussion: PC is a rare endocrine neoplasm, where parathyroid adenoma and parathyroid hyperplasia are highlighted as the most frequent forms of PC presentation, with a tendency for symptomatic presentation and increasing the risk of neoplasms in other organs . It is usually sporadic or may be found in association with other pathologies such as multiple endocrine neoplasia 1 and 2 (MEN 1 and MEN 2), isolated familial hyperparathyroidism or hyperparathyroidism with jaw tumor (1 Presentation: Monday, July 14, 2025