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

Abstract

Background: 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.

Keywords: mortality; thyroid cancer; trend.