Decreasing Disease-Specific Mortality of Differentiated Thyroid Cancer in Korea: A Multicenter Cohort Study

Recent studies have reported improved survival in patients with thyroid cancer. This study evaluated the changes in disease-specific survival (DSS) of patients with differentiated thyroid cancer (DTC) in association with clinicopathologic characteristics from 1996 to 2005 in Korea. Methods: This was a retrospective, multicenter cohort study. A total of 4398 DTC patients were included, and they were classified according to the year of initial surgery: 1996-2000 (period 1), 2001-2003 (period 2), and 2004-2005 (period 3). Results: During the study period, patient age and the proportion of papillary thyroid cancer increased gradually. Primary tumors became smaller (2.3 ± 1.4 cm at period 1 to 1.5 ± 1.2 cm at period 3; p < 0.001). The proportion of high-volume lymph node metastases decreased significantly (20% at period 1 to 13% at period 3; p for trend <0.001). DSS differed significantly according to period during the median 10 years follow-up (p = 0.002). The 10-year DSS rates were 98.0%, 98.7%, and 99.2% in periods 1, 2, and 3, respectively. After adjusting for various characteristics, the disease-specific mortality risk was significantly lower during period 2 (hazard ratio = 0.49 [confidence interval CI 0.25-0.90], p = 0.021) and period 3 (hazard ratio = 0.40 [confidence interval 0.21-0.77], p = 0.006) compared to that of period 1. This trend was also significant in a subgroup analysis of low (I-II) and high (III-IV) TNM stages. Conclusions: The disease-specific mortality of patients with DTC in Korea decreased over time. Earlier detection of small DTCs with less extensive disease and standardization of treatment may be associated with this phenomenon.