Endocrine Abstracts (2017) 49 EP191 | DOI: 10.1530/endoabs.49.EP191

Biology and differential diagnosis of calcitonin secreting neuroendocrine tumors

Bojana Popovic, Djuro Macut, Valentina Elezovic Kovacevic, Tatjana Isailovic, Ivana Bozic Antic, Tamara Bogavac, Dusan Ilic, Sanja Ognjanovic, Gordana Rodic, Milan Petakov & Svetozar Damjanovic

Clinic for Endocrinology, Diabetes and Metabolic Diseases, Clinical Center of Serbia, Belgrade, Serbia.

Introduction: Calcitonin secreting neuroendocrine tumors (NET) are rare and not well recognized. Due to many similarities, it is sometimes difficult to differentiate them from medullary thyroid carcinoma (MTC), which can hamper choice of proper therapy. We investigated our group of patients with this type of NET in terms of diagnosis and biology.

Patients and Methods: We analyzed 38 patients with calcitonin secreting NET (5% of all our patients with NET). In addition to standard work up, calcium-stimulation test for calcitonin was performed in 15 of them, and results compared to 34 patients with MTC, and 21 control subjects with elevated calcitonin level and thyroid pathology other than MTC. Statistical analysis was done with SPSS software.

Results: Primary localization of NET was lung (16), pancreas (12), unknown primary (8) and intestine (2), with majority (54.1%) being grade G3, and high majority being metastatic (94.7%). Majority (55.6%) had goiter and 26.3% concomitant TPOAb, while 28.9% co-secreted another hormone (ADH, insulin, serotonin, PTHrP). Patients with NET had significantly higher basal calcitonin levels compared to controls (P(0.01), but with no significant difference compared to patients with MTC (P=0.427). Unlike this, patients with NET achieved significantly lower calcitonin levels after calcium stimulation compared to patients with MTC (P(0.01), but no different compared to controls (P=0.102). There was no significant correlation between basal calcitonin level and presence of TPOAb (P=0.816) or goiter (P=0.670) in these patients. Their median overall survival was 24.0 months (95% CI 10.9–37.1).

Conclusion: Patients with calcitonin secreting NET can secrete very high calcitonin levels, but can be differentiated from patients with MTC by absence of significant response to stimulation with calcium. Survival of these patients is poor, but influence of calcitonin on survival is yet to be determined.