Prognostic value of ¹⁸F-fluorodeoxyglucose-positron emission tomography in patients with differentiated thyroid carcinoma and circulating antithyroglobulin autoantibodies

Objective: To explore the prognostic value of F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) in radioiodine-negative patients with differentiated follicular cell-derived thyroid carcinoma with circulating antithyroglobulin autoantibodies (TgAb). Methods: We retrospectively reviewed cases of all patients with differentiated thyroid cancer and increased TgAb referred for FDG-PET at Mayo Clinic, Rochester, Minnesota, from August 2001 to December 2004. PET findings were compared with results of other imaging and laboratory studies. Follow-up information was recorded until 19 December 2009. Results: Of the 17 patients identified, PET results were true positive in 10 and false negative in two. In eight of these 12 patients with confirmed residual or recurrent disease, the increased TgAb level persisted and the disease progressed. In four of the 12 patients, TgAb decreased or disappeared after further treatment. In five patients, no residual or recurrent disease was found during follow-up. PET results were true negative in these five patients; TgAb disappeared spontaneously in four of these patients. Conclusions: Negative PET results were associated with the absence of active disease and disappearing TgAb over time. FDG-avid residual lesions were associated with more aggressive disease and persistently increased TgAb.