¹⁸F-FDG uptake as a prognostic variable in primary differentiated thyroid cancer incidentally detected by PET/CT: a multicentre study.
OBJECTIVE
Our aim was to investigate the association between (18)F-fluorodeoxyglucose (FDG) uptake and event-free survival in patients in whom a differentiated thyroid cancer (DTC) was detected by (18)F-FDG positron emission tomography (PET)/CT.


METHODS
Among 884 focal (18)F-FDG PET thyroid incidentalomas referred to our 4 Nuclear Medicine Departments, we investigated 54 patients in whom a DTC was confirmed and a clinical follow-up was available. The ratio between maximum standardized uptake value (SUVmax) of DTC and SUVmean of the liver (SUV ratio) was recorded for each scan. All patients underwent total thyroidectomy and (131)I remnant ablation. After a median follow-up of 39 months we assessed the outcome. The association between disease persistence/progression, (18)F-FDG uptake and other risk factors (T, N, M and histological subtype) was evaluated through univariate and multivariate analyses.


RESULTS
Of the 54 patients, 39 achieved complete remission. The remaining 15 showed persistence/progression of disease. High (18)F-FDG uptake, i.e. SUV ratio ≥3, showed a low positive predictive value (48 %). Low (18)F-FDG uptake (SUV ratio < 3) displayed a high negative predictive value (93 %). The median of SUV ratios in T1-T2 (2.2), in M0 (2.7) and in non-virulent subtypes (2.7) were significantly lower (p < 0.03) than in T3-T4 (5.0), M1 (7.3) and virulent subtypes (6.0). Kaplan-Maier analysis showed a significant association between high (18)F-FDG uptake and disease persistence/progression (p = 0.001). When we adjusted risk estimates by using a multivariate Cox model, only T (p = 0.05) remained independently associated with disease persistence/progression.


CONCLUSIONS
An intense (18)F-FDG uptake of the primary DTC is associated with persistence/progression of disease. However, when all other prognostic factors have been taken into account, (18)F-FDG uptake does not add further prognostic information.
Department of Nuclear Medicine, Galliera Hospital, Genoa, Italy, arnoldo.piccardo@galliera.it.
Arnoldo
A
Piccardo
Matteo
M
Puntoni
Francesco
F
Bertagna
Giorgio
G
Treglia
Luca
L
Foppiani
Federico
F
Arecco
Raffaele
R
Giubbini
Mehrdad
M
Naseri
Angelina
A
Cistaro
Manlio
M
Cabria
Francesca
F
Bardesono
Luca
L
Ceriani
Fabio
F
Orlandi
Luca
L
Giovanella
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018572:Disease-Free Survival; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D033162:Incidental Findings; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011237:Predictive Value of Tests; D019275:Radiopharmaceuticals; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18