Background: Because patients with differentiated thyroid carcinoma (DTC) presenting with distant metastasis (DM) have a particularly poor prognosis, examining the prognostic factors in this group is essential. We aimed to evaluate the prognostic factors affecting cancer-specific survival (CSS) in DTC patients presenting with DM.
Methods: Of the 1227 DTC patients, 51 (4.2 %) presented with DM at diagnosis. All patients underwent a total thyroidectomy, followed by radioiodine (RAI) ablation and postablation whole body scan (WBS). Patients were considered to have an osseous metastasis if one of the metastatic sites involved a bone, while RAI avidity was determined by any visual uptake in a known metastatic site on the first WBS. Factors predictive of CSS were determined by univariate and multivariate analyses by the Cox proportional hazard model.
Results: In univariate analysis, older age (relative risk [RR] 1.050, 95 % confidence interval [CI] 1.010-1.091, P = 0.014), DM discovered before WBS (RR 3.401, 95 % CI 1.127-10.309, P = 0.030), follicular thyroid carcinoma (RR 3.095, 95 % CI 1.168-8.205, P = 0.025), osseous metastasis (RR 4.695, 95 % CI 1.379-15.873, P = 0.013), non-RAI avidity (RR 3.355, 95 % CI 1.280-8.772, P = 0.014), and external beam radiotherapy to DM (RR 3.241, 95 % CI 1.093-9.614, P = 0.034) were significant poor prognostic factors for CSS. In the multivariate analysis, after adjusting for other factors, osseous metastasis (RR 6.849, 95 % CI 1.495-31.250, P = 0.013) and non-RAI avidity (RR 7.752, 95 % CI 2.198-27.027, P = 0.001) were the two independent poor prognostic factors for CSS. Older age almost reached statistically significance (RR 1.055, 95 % CI 0.996-1.117, P = 0.068).
Conclusions: DTC patients presenting with DM accounted for 4.2 % of all patients. Because osseous metastasis and RAI avidity were independent prognostic factors, future therapy should be directed at improving the treatment efficacy of osseous and/or non-RAI-avid metastases.