Thyroid cancer is increasing all over the world. The exact cause of this 
increase is still debated and there are conflicting reports. Sophisticated 
molecular studies suggest that environmental chemicals may have effects of 
thyroid carcinogenesis. The development of powerful molecular biology techniques 
has enabled targeted next-generation sequencing for detection of mutations in 
thyroid cancer, and this technique can make a specific diagnosis of thyroid 
cancer in cytologically indeterminate cases. The initial treatment of 
well-differentiated thyroid cancer (DTC) is surgery followed by radioiodine 
remnant ablation. However, further studies are needed to determine the optimal 
dosage of radioactive iodine for DTC patients with lateral neck metastasis. DTC 
is an indolent tumor and may cause death even decades later. Thus, long-term 
follow-up is mandatory. Recently, dynamic risk stratification (DRS) has begun to 
use stimulated thyroglobulin level at 1 year after the initial treatment and 
restratified the risk in accordance with the response to the initial treatment. 
This DRS strategy accurately predicts disease free survival and can be widely 
used in daily clinical settings. For the iodine refractory metastatic disease, 
redifferentiation therapy and targeted therapy are two promising alternative 
treatments. Sorafenib is the first approved agent for the treatment of 
progressive iodine refractory advanced thyroid cancer in Korea and may be very 
helpful for radioactive-refractory locally advanced or metastatic DTC. 
Selumetinib may be an effective redifferentiating agent and could be used within 
several years.