SUN-315 Flushing as an Early Clinical Indicator of Medullary Thyroid Cancer

Abstract Disclosure: A. Melanthiou: None. M.A. Incer-Obando: None. M. Bhalla: None. R. Galagan: None. Background Medullary thyroid cancer (MTC) is a rare, aggressive thyroid cancer originating in calcitonin-producing C cells. It is often associated with a RET proto-oncogene mutation, causing Multiple Endocrine Neoplasia (MEN) 2A and 2B. Unlike papillary and follicular thyroid cancers, MTC does not respond to radioiodine therapy, underscoring the importance of early detection for timely surgical treatment and MEN2 screening. Diagnosis is typically made by FNA cytology of a thyroid nodule, elevated serum calcitonin and/or CEA levels. We report a case of an adult female with flushing as the initial manifestation of MTC. CaseA 22-year-old healthy female was referred to Endocrinology for facial flushing. She reported daily episodes of facial erythema associated with burning sensation and warmth, occurring for five months. On physical exam, her vitals were BP 116/78mmHg, HR 90bpm, and temperature 98.2°F. Notably, she had warm, blanching erythema involving the face, ears, neck and upper chest along with a few telangiectasias. Neck exam revealed a palpable, firm, nontender 2-3cm left thyroid nodule with no lymphadenopathy. Initial laboratory evaluation showed a TSH of 2.02 (0.50 - 5.00 uIU/mL), free T4 1.15 (0.6-1.15 ng/dL), PTH 36 (12.0 - 65.0 pg/mL), Metanephrines 30.4 (0.0 - 88.0 pg/mL), Normetanephrines 73.8 (0.0 - 210.1 pg/mL), 5-HIAA 4.3 (<22 ng/mL), Tryptase 7.2 (2.2-13.2 ug/L) and Calcitonin 5392 (0.0 - 5.0 pg/mL). Following the discovery of a markedly elevated calcitonin level, the patient was contacted for a biopsy of the thyroid nodule. Thyroid ultrasound revealed a left thyroid nodule 3.8 x 1.7 x 2.7 cm, which was solid, hypoechoic, wider than tall, and no calcifications; TR-4. FNA of the nodule confirmed MTC with positive calcitonin immunochemical staining. Notably, the patient’s flushing increased after biopsy. She was referred to endocrine surgery and underwent a total thyroidectomy. Surgical pathology revealed MTC with negative margins and lymph nodes. Genetic analysis was in process. The patient reported complete resolution of her flushing symptoms after surgery. Discussion: The incidence of flushing in MTC is estimated to be 10-20% of cases, influenced by tumor size, aggressiveness and whether the cancer is part of a hereditary syndrome like MEN 2. Our patient’s flushing involved the face, neck and upper torso, and occurred without diaphoresis, pruritus, or urticaria. Her elevated calcitonin was the presumed vasoactive mediator of her flushing, although MTCs can secrete additional vasoactive substances including prostaglandins, levodopa, and substance P. Her flushing resolved with tumor resection and normalization of calcitonin. As demonstrated by this case report, thoroughly investigating the cause of flushing is important as it may be the first clue of an endocrine disorder that requires specific surgical and/or medication intervention. Presentation: Sunday, July 13, 2025