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Diagnostic Accuracy of 18F-FDG PET/CT in Patients With Biochemical Evidence of Recurrent, Residual, or Metastatic Medullary Thyroid Carcinoma

Rodríguez-Bel, Laura, MD*; Sabaté-Llobera, Aida, MD*; Rossi-Seoane, Susana, MD*; Reynés-Llompart, Gabriel, MSc*; Vercher Conejero, José Luis, MD*; Cos-Domingo, Mònica, MD; Moreno-Llorente, Pablo, MD, PhD; Pérez-Maraver, Manuel, MD, PhD§; Cortés-Romera, Montserrat, MD, PhD*; Gámez Cenzano, Cristina, MD, PhD*

doi: 10.1097/RLU.0000000000002414
Original Articles

Objective 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.

Methods 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).

Results 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).

Conclusions 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

Radiology-IDI,

Surgery, and

§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: laura.rodriguez@idi.gencat.cat.

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