Background: Although differentiated thyroid cancer (DTC) has relatively favorable course, factors predicting the course of the disease are intensively searched. The aim of the study was to identify the clinical factors determining incomplete response to radioiodine therapy in patients with DTC.
Methods: We retrospectively analyzed 385 consecutive patients with DTC treated and followed-up at a single tertiary reference center. We investigated clinical factors detectable during first hospitalization 3-6 months following total thyroidectomy due to DTC, which may serve as prognostic factors determining response to DTC therapy in a long-term follow-up.
Results: Stimulated thyroglobulin (sTg) was the only parameter significantly correlated with the cumulative radioiodine activity (r=0.247, P<0.001). The need for repeated radioiodine administration (≥3 doses) was best predictable on the basis of sTg concentration assessed at the moment of qualification to radioiodine therapy (P=0.003). Predictive value of the sTg for incomplete response to radioiodine has been confirmed with the ROC curve analysis and the best proposed cut-off value was 8.17 ng/mL (sensitivity 55%, specificity 77%, positive predictive value 42.1%, negative predictive value 84.7%); sTg over 8.17 ng/mL increases the risk of incomplete response to therapy 2.5-folds (P=0.002).
Conclusions: sTg, assessed at the moment of qualification to radioiodine therapy, as the most important factor determining incomplete response to radioiodine therapy in patients with DTC, should be particularly taken into consideration in predicting the future course of the disease as well as treatment and follow-up planning. Radical thyroidectomy may help to increase the effectiveness of treatment.