Prognosis of Differentiated Thyroid Carcinoma with Initial Distant Metastasis: A Multicenter Study in Korea

Abstract

Background: Most patients with differentiated thyroid cancer (DTC) have a favorable prognosis. However, patients with DTC and initial distant metastasis have not been commonly found, and their clinical characteristics have seldom been reported. In this study, we analyzed the clinical features and prognosis of patients with DTC and initial distant metastasis in Korea.

Methods: We retrospectively reviewed the clinical data of 242 patients with DTC and initial distant metastasis treated from 1994 to 2013, collected from five tertiary hospitals in Korea.

Results: The patients' median age was 51 years, and 65% were women. They were followed for a median of 7 years. Lung was the most common site of distant metastasis: only lung 149 patients (62%), only bone 49 (20%), other single site one (pleura), and combined sites 43 (40 were lung and bone, two were bone and other site, and one was lung and other site). At the time of diagnosis, 50 patients (21%) had non-radioactive iodine (RAI) avidity. Five-year disease-specific survival (DSS) was 85% and 10-year DSS was 68%, which were better than those in previous studies. After multivariate analysis, old age, male sex, metastatic site, and histologic type (follicular type) were significant factors for poor prognosis. However, negative RAI avidity status was not a significant prognostic factor after adjusting for other variables.

Conclusion: The prognosis of Korean patients with DTC and initial distant metastasis was better than in previous studies. Old age, male sex, metastasis site, and histologic type were significant prognostic factors.

Keywords: Differentiated thyroid cancer; Neoplasm metastasis; Prognosis; Radioactive iodine.

Fig. 1. Classification of initial distant metastasis in this study. A total of 242 patients were diagnosed with initial distant metastasis. Patients were classified according to site of distant metastasis. Diagnoses were as follows: 149 with lung only, 49 with bone only, and 43 with combined metastasis. One patient was diagnosed with other site only metastasis. Lung metastasis was subdivided into micronodular, macronodular, and miliary metastasis. Bone metastasis was subdivided into solitary and multiple metastases.

Fig. 2. Survival analysis according to risk factors in patients with differentiated thyroid carcinoma and initial distant metastasis. A Kaplan-Meier analysis and log-rank test were used to evaluate the risk factors for disease-specific death (DSD). (A) Age (>55 years), (B) male sex, (C) tumor histology (follicular thyroid carcinoma [FTC] rather than papillary thyroid carcinoma [PTC]), (D) radioactive iodine (RAI) avidity (non-RAI avidity), and (E) metastatic site were significant risk factors for DSD. HTC, Hürthle cell carcinoma.

Fig. 3. Prognostic factors according to change of age. When the prognostic factors site of distant metastasis, tumor histology, and radioactive iodine (RAI) avidity were stratified according to age, (A) the bone only/combined metastasis group, (B) follicular thyroid carcinoma (FTC), and (C) non-RAI avidity were increased with age. However, lung only group, papillary thyroid carcinoma (PTC), and RAI avidity decreased according to age. HTC, Hürthle cell carcinoma.