Endocrine Abstracts

Introduction: Basal calcitonin (bCT) and calcium-stimulated calcitonin (sCT) levels are useful in the management of Medullary Thyroid Cancer (MTC). Nowadays several bCT/sCT cut-offs have been proposed but univocally accepted values are still lacking. We identified gender-specific CT cut-offs in a series of patients who performed calcium gluconate test at our Centre.

Methods: Our study includes a total of 35 patients (12 males and 23 females) with thyroid nodules and biochemical suspect of MTC that performed calcium gluconate test from 2017 to 2023 and underwent total thyroidectomy according to available sCT cut-off reported in literature (until 2020 in males bCT 68 pg/ml, sCT 544; in females bCT 26, sCT 79; since 2021 in males bCT 34, sCT 466; in females, bCT 30, sCT 79). Patients with RET gene mutation were excluded. We compared bCT and sCT levels with histological results in order to define best internal cut-offs to predict diagnosis of MTC.

Results: The best cut-offs of bCT and sCT for the diagnosis of MTC were: >29.6 pg/ml (Sensitivity, Sn 85.7%, Specificity, Sp 100%, Diagnostic accuracy, DA 91.6%, P<0.0001) and >1242 pg/ml (Sn 57.1%, Sp 100%, DA 75%, P=0.12) in males; >14.6 pg/ml (Sn 100%, Sp 90%, DA 95.6%; P<0.0001) and >442 pg/ml (Sn 61.5%, Sp 90%, DA 73.9%, P=0.08) in female. According to these cut-off values, bCT was able to identify MTC in 100% of females and 85.7% of males (one male case of MTC with both negative bCT and sCT underwent total thyroidectomy for symptomatic goitre). With bCT we didn’t have false positive cases in males and we had one false positive case in females. Conversely, sCT showed an inadequate diagnostic accuracy and a non-negligible risk of misdiagnosis. If we had applied only sCT cut-offs in order to decide for surgery, we would have had missed 7 patients with MTC (2 males, 5 females). Indeed, these patients had positive bCT and negative sCT and underwent thyroidectomy according to available sCT cut-off at the time of surgery.

Conclusions: In our series bCT had higher diagnostic accuracy than sCT for diagnosis of sporadic MTCs. Stimulated test seems to provide no diagnostic improvement as compared to bCT and, given its low sensitivity, it may lead to miss some MTCs cases that could be correctly identified by bCT.