RF07 | PSUN366 An Uncommon Path Leading to Diagnosis of Multiple Endocrine Neoplasia 2A

Abstract Introduction MEN2 is a rare Autosomal Dominant disorder resulting from mutations in the RET proto-oncogene. MEN2 is classified into two distinct syndromes: MEN2A and MEN2B. MEN2A is a syndrome that presents with Medullary Thyroid Carcinoma (MTC) in 90% of adult gene carriers, unilateral or bilateral pheochormocytoma in 50%, and multigland parathyroid tumors in 20-30% of affected individuals. Other rare variants of MEN2 include Familial Medullary Thyroid Carcinoma (FMTC), MEN2A with cutaneous lichen amyloidosis, and MEN2A or FMTC with Hirschprung's disease. We present a patient with incidentally noted elevated calcitonin levels, later diagnosed with MEN2A. Clinical Case 37-year-old Caucasian male was referred to our clinic for elevated calcitonin levels noted on lab work done as part of evaluation and management for weight loss prior to initiating GLP-1 agonists. He was diagnosed with hypothyroidism and multinodular goiter and started on Synthroid. His only symptoms were weight gain, tiredness, soft stools and facial flushing He denied any family history of endocrine disorders. Physical exam was unremarkable. Pertinent labs included serum calcitonin 93 pg/mL (<10 pg/mL), serum CEAg 5.2 ng/mL (0-3 ng/mL), and work up for pheochromocytoma and hyperparathyroidism was negative. USG thyroid showed a left lobe thyroid nodule measuring 7×5×7 mm with macrocalcifications, a right lobe thyroid nodule measuring 8×5×10mm, and an abnormal left lateral level III LN. He underwent left thyroid lobectomy with level VI neck dissection (total thyroidectomy aborted due to hypoxia), and subsequently completion thyroidectomy with right central neck dissection. Pathology showed metastatic MTC with pathologic staging pT1aN1a. Genetic testing showed RET c. 1826G>A (p. C609Y) which is ATA – MOD risk. Patients’ father was also genetically screened and diagnosed with MEN2A and noted to have elevated calcitonin levels. He also subsequently underwent total thyroidectomy, which revealed medullary thyroid microcarcinoma. Conclusion A number of studies support that measurement of serum calcitonin is the most sensitive screening test for detecting occult MTC in individuals with thyroid nodules. Yet, the use of serum calcitonin in the routine evaluation of thyroid nodules is controversial due to absence of uniform calcitonin thresholds, high false positive values and unavailability of pentagastrin stimulation testing. Moreover, there are no recommendations based on the current data to check calcitonin levels prior to initiating GLP-1 agonists but their use is not recommended in patients with personal or family history of MTC/MEN2. Based on the above case, measurement of calcitonin levels should be a part of the work up in patients who present with thyroid nodules and are receiving GLP-1 agonists. Attention should also be paid to the importance of genetic counseling in first-degree relatives of patients with MEN2A. This allows for timely diagnosis and reduces morbidity and mortality. Presentation: Saturday, June 11, 2022 1:30 p.m. - 1:35 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.