Medullary thyroid carcinoma (MTC) is a rare malignancy. Location of residual, recurrent, or metastatic disease is crucial to treatment management and outcome. We aimed to evaluate the use of 18F-FDG PET/CT in localizing MTC foci in patients with biochemical relapse.
This is a retrospective cohort study. Review of 51 FDG PET/CT studies of 45 patients referred to restage MTC due to increased calcitonin (Ctn) and carcinoembryonic antigen (CEA) values at follow-up. FDG PET/CT diagnostic accuracy was determined through a patient-based analysis, using histology as criterion standard when available, or other imaging studies and clinical follow-up otherwise (mean, 4 years).
There were 25 positive scans. Sensitivity, specificity, positive and negative predictive values, diagnostic accuracy, and positive likelihood ratio were 66.7%, 83.3%, 88.0%, 57.7%, 72.5%, and 4.0, respectively. Using a Ctn cutoff of 1000 pg/mL, sensitivity increased to 76.9%. There were significant differences of Ctn and CEA values between positive and negative FDG PET/CT (P < 0.05). Regarding true-positive studies, average SUVmax comparing locoregional and metastatic disease was at the limit of significance (P = 0.046).
PET/CT can be useful to restage patients with biochemical relapse of MTC, with a better performance in higher Ctn levels. Its high positive predictive value (88%) may impact in the therapeutic management, although its low negative predictive value (57.7%) makes strict follow-up mandatory in examinations without pathologic findings.
From the *PET Unit, Department of Nuclear Medicine-IDI, and Departments of
§Endocrinology, Hospital Universitari de Bellvitge-IDIBELL, L'Hospitalet de Llobregat, Barcelona, Spain.
Received for publication June 23, 2018; revision accepted October 25, 2018.
Conflicts of interest and sources of funding: none declared.
Correspondence to: Laura Rodriguez-Bel, MD, Hospital Universitari de Bellvitge, PET Unit, Department of Nuclear Medicine-IDI, IDIBELL, l'Hospitalet de Llobregat, Barcelona, Spain. E-mail: email@example.com.