MON-329 Calcitonin-Secreting Neuroendocrine Tumor Raising Concern for Medullary Thyroid Carcinoma in a Patient with Thyroid Nodules

Background: Calcitonin elevation is a characteristic feature of medullary thyroid carcinoma, but can also be secreted by other neuroendocrine tumors. Pancreatic neuroendocrine tumor is a rare entity, with most functioning tumors secreting insulin and gastrin, while other hormones such as calcitonin are not commonly evaluated. Case: A 63 year old woman with stage 4, well differentiated pancreatic neuroendocrine tumor was referred for evaluation of a thyroid nodule and rising calcitonin level concerning for possible medullary thyroid cancer. She presented with persistent diarrhea and weight loss, and found to have a 10 cm pancreatic mass, liver metastasis and common bile duct obstruction requiring a biliary drain. Pathology showed grade 2, well differentiated neuroendocrine neoplasm with 5/10 mitoses/high power field, immunopositive for chromogranin, synaptophysin and Cam5.2, very faint, rare staining for gastrin and negative for somatostatin. Chromogranin A was 21 (Nl 25-140 ng/mL), serotonin 641 (Nl 56-244 ng/mL), gastrin 16 (Nl <100pg/mL), 24 hr 5HIAA 3.3 (Nl <6mg/24h), pancreatic polypeptide <50 pg/mL (Nl <1823 pg/mL), vasoactive intestinal peptide <5 pg/mL (Nl <75 pg/mL) and somatostatin 33 (Nl <30). She was treated with radioablation of the liver lesions and monthly lanreotide injections. An Octreoscan showed a questionable focus of abnormal uptake within the right thyroid lobe, triggering a calcitonin level that was elevated at 722 pg/mL (Nl <5pg/mL). She was referred for thyroid nodule biopsy to rule out medullary thyroid cancer. Ultrasound of the thyroid gland showed bilateral thyroid nodules with a dominant, right mid thyroid nodule measuring 13.9 x 16. 4 x 18.5 mm, hyperechoic, spongiform with regular, smooth and well defined margins and no calcifications. FNA biopsy of the right mid thyroid nodule was negative for malignant cells, consistent with benign follicular nodule with cystic degeneration, and immunohistochemical staining for calcitonin of the cell block was negative. Immunostaining of the prior pancreatic tumor biopsy for calcitonin was performed and positive. Conclusion: Although elevation in calcitonin raises concern for medullary thyroid cancer, it is rarely secreted by other neuroendocrine tumors. Thus, a, calcitonin-secreting pancreatic neuroendocrine tumor is an important entity to consider as a cause of elevated calcitonin, especially in a patient with benign appearing thyroid nodules. Reference: 1 Jensen, R et al, ENETS Consensus Guidelines for the Management of Patients with Digestive Neuroendocrine Neoplasms: Functional Pancreatic Endocrine Tumor Syndromes. Neuroendocrinology. 2012;95:98-119.