BACKGROUND Distant metastasis, generally to lung and bone, is rare in differentiated thyroid carcinoma (DTC) and the prognosis is still elusive. We investigated long-term outcomes of lung metastasis in DTC patients and its prognostic factors.

METHODS A retrospective review was performed of 4572 patients who underwent surgery for DTC from 1962 to 2009 at Seoul National University Hospital. Among them, 164 patients were identified with lung metastasis and 152 patients were enrolled in the final analysis. Poor prognosis was defined as progressive disease or death.

RESULTS Of these 152 patients, 10- and 20-year survival rates were 85.0% and 71.0%, respectively. No evidence of disease, stable disease, progressive disease, and death was identified in 22.4%, 28.3%, 35.5%, and 13.8%, respectively, after 11 years of median follow-up (range 2-41 years). Older age at diagnosis (≥45 years), primary tumor size ≥2 cm, follicular thyroid cancer, metastasis diagnosed after initial evaluation or (131)I remnant ablation (late metastasis), multiple metastases other than lung, (131)I nonavidity, and the presence of macronodules (≥1 cm) were more frequent in poor prognoses. Cox proportional hazard ratio for progression-free survival showed that (131)I nonavidity was the only independent predictive factor for poor prognosis.

CONCLUSIONS The prognosis of lung metastasis from DTC in Korea within this study was favorable. (131)I nonavidity, observed more frequently in late metastasis, was the only independent factor predicting poor prognosis.