Secretive and proliferative tumor profile helps to select the best imaging technique to identify postoperative persistent or relapsing medullary thyroid cancer

In patients with postoperative persistent medullary thyroid cancer (MTC), the tumor detection rate is generally low for most of the imaging techniques now available. The aim of this study was to investigate if the clinico-biological profile of the tumor may indicate which imaging technique to perform in order to identify postoperative persistent or relapsing MTC foci. Thirty-five consecutive MTC patients with detectable and progressively increasing postoperative serum concentrations of calcitonin were enrolled in the study. The detection rates of 18F-deoxy-d-glucose (FDG)-positron emission tomography (PET), somatostatin receptor scintigraphy (SRS), and 131I-metaiodobenzylguanidine scintigraphy (MIBG) were compared in relation with calcitonin and carcinoembryonic antigen serum concentrations, Ki-67 score and results of conventional imaging techniques (CIT). FDG-PET positivity was significantly associated with calcitonin serum concentrations >400 pg/ml and Ki-67 score >2.0% (P<0.05), while SRS positivity was associated with calcitonin serum concentrations >800 pg/ml (P<0.05). SRS positivity significantly correlated with tumor appearance at CIT (P<0.01), while FDG-PET was positive in nine CIT-negative patients. The secretive and proliferative tumor profile may guide the choice of the imaging technique to use in the follow-up of patients with MTC. A Ki-67 score >2.0% suggests to perform a FDG-PET in addition to conventional imaging. Calcitonin secretion predicts both FDG-PET and SRS uptake but SRS positivity is generally found only in patients with well defined MTC lesions that are also detectable at the conventional imaging examination. MIBG outcome is not predicted by any clinico-biological factors here investigated.