The incidence of thyroid cancer in focal hypermetabolic thyroid lesions: an 18F-FDG PET/CT study in more than 6000 patients.
BACKGROUND
The clinical significance of incidental thyroid abnormalities discovered in fluorine-18 fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) (FDG PET/CT) studies remains controversial. The aim of this large retrospective study was to (a) determine the prevalence of focal F-FDG thyroid uptake on whole-body F-FDG PET/CT studies carried out for nonthyroid cancers and (b) to test whether intense focal F-FDG thyroid uptake is associated with malignancy.


METHODS
A total of 11 921 F-FDG PET/CT studies in 6216 patients carried out at our institution between January 2012 and December 2014 were analyzed. We retrospectively reviewed the medical records of these patients. Eight hundred and forty-five/6216 (13.6%) patients had a thyroid incidentaloma on the basis of the clinical F-FDG PET/CT report. One hundred and sixty/845 (18.9%) of these underwent ultrasound and 98 (61.3%) of these underwent a fine-needle aspiration (FNA). Twenty-six of these 98 (26.5%) patients underwent thyroidectomy. Thyroid lesion and background standardized uptake value (SUVs) for each patient were measured upon review of the F-FDG PET/CT study. We measured maximum standardized uptake value (SUVmax), thyroid to background TL/TBG, thyroid to bloodpool TL/BP and thyroid to liver TL/L ratios in benign and malignant lesions. Receiver operating curves were calculated to determine optimal cut-off values between malignant and benign lesions.


RESULTS
Twenty-one of the 98 patients who underwent FNA biopsy or thyroidectomy had malignant disease (21.4%). Malignant lesions had significantly higher thyroid lesion SUVmax, TL/TBG, TL/BP, and TL/L than benign nodules. The receiver operating curves derived cut-off ratio TL/TBG of more than 2.0 differentiated benign from malignant lesions best with a specificity and sensitivity of 0.76 and 0.88, respectively.


CONCLUSIONS
The incidence of malignancy in biopsied focal hypermetabolic thyroid lesions is 21.4%. Lesions on F-FDG PET/CT studies, with a ratio TL/TBG more than 2.0, warrant further work-up with ultrasound and FNA to exclude malignancy.
aDepartment of Molecular and Medical Pharmacology bJonsson Comprehensive Cancer Center cSection of Endocrine Surgery, Department of Surgery dDepartment of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, USA eDepartment of Nuclear Medicine, Universitätsklinikum Essen, Essen, Germany.
Martin
M
Barrio
Johannes
J
Czernin
Michael W
MW
Yeh
Miguel F
MF
Palma Diaz
Pawan
P
Gupta
Martin
M
Allen-Auerbach
Christiaan
C
Schiepers
Ken
K
Herrmann
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18; D006801:Humans; D015994:Incidence; D033162:Incidental Findings; D008297:Male; D008875:Middle Aged; D000072078:Positron Emission Tomography Computed Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D013961:Thyroid Gland / Q000000981:diagnostic imaging* / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000378:metabolism; D055815:Young Adult
D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18