Changes in the Clinicopathological Characteristics and Outcomes of Thyroid Cancer in Korea over the Past Four Decades

Background: Thyroid cancer has increased globally, with a prominent increase in small, papillary thyroid cancers (PTC). The Korean population has a high iodine intake, high prevalence of BRAF V600E mutations, and family histories of thyroid cancer. We examined the clinicopathological characteristics and outcomes of thyroid cancers in Korean patients over four decades. Methods: The medical records of 4500 thyroid cancer patients, between 1962 and 2009 at a single center, including 3147 PTC patients, were reviewed. Results: The mean age of the patients was 46.8 +/- 13.2 years; women accounted for 82.9% of the patients, and the median follow-up duration was 4.8 years (mean 7.0 +/- 5.8 years, range 1-43 years). The number of patients visiting the clinic increased from 411 during 1962-1990 to 2900 during 2000-2009. Age at diagnosis increased from 39.6 +/- 12.9 to 48.6 +/- 12.4 years. The male to female ratio increased from 1: 6 to 1:4.5. The proportion of small (< 1 cm) tumors increased from 6.1% to 43.1%, and the proportion of cancers with lymph node (LN) involvement or extrathyroidal extension (ETE) decreased from 76.4% to 44.4% and from 65.5% to 54.8% respectively. Although there were decreases in the proportion of LN involvement and ETE, these decreasing rates were not proportional to the expected rates based on the decreased proportion of large tumors. The overall recurrence and mortality rates were 13.3% and 1.4%. The five-year recurrence rate significantly decreased (from 11% to 5.9%), and the five-year mortality also improved (from 1.5% to 0.2%). Conclusions: The incidence of thyroid cancer has rapidly increased, with a decrease in tumors of large size, LN involvement, and ETE, although the decreasing rates of LN involvement and ETE were not as prominent as decreasing rates of large size tumors. The mortality and recurrence rates have also decreased. Future long-term follow-up of patients diagnosed in the most recent decade is needed to confirm the prognostic characteristics of Korean PTC patients.