Thyroid cancer has the highest incidence rate among female cancers. It ranks third among all cancers. Recently, public awareness has increased through media and the Internet, but there are many misunderstandings due to incorrect information. Most cases have a high cure rate, but there is also incurable thyroid cancer with a high mortality rate. At the 'Gangnam Health Talk Show' held at the Gangnam District Office in Seoul in December last year, with around 200 citizens in attendance, various treatment information on thyroid cancer was shared. We learned more about incurable thyroid cancer with the help of Jang Hang-seok, director of the cancer hospital at Gangnam Severance Hospital, who attended as a lecturer that day. ● Is thyroid cancer a good cancer? Thyroid cancer is largely divided into four types: papillary cancer, follicular cancer, medullary cancer, and undifferentiated cancer. In addition, there are malignant lymphoma, squamous cell carcinoma, and cancer that has metastasized to the thyroid gland. Unlike other countries, papillary cancer accounts for more than 95% of cases in Korea. Papillary cancer is frequently found in areas where people consume a lot of seaweeds with high iodine content, such as laver and kelp. On the other hand, follicular cancer is relatively common in areas lacking iodine. Papillary cancer and follicular cancer are easily treated, to the point where they are called “good cancers.” However, if left untreated for a long time, they can turn into poorly differentiated cancers or cancers that are incurable. Director Jang said, “Thyroid cancer is not aggressive and spreads slowly, so it is relatively easy to treat among cancers. They say there is no need to worry, but there may be differences in long-term observation results.” Like other cancers, the first surgery is important for thyroid cancer. If the first surgery is not perfect, the recurrence rate is high. Director Jang explained, “There are many cases where thyroid cancer is found to be intractable because it has progressed a lot from the time of initial diagnosis and is difficult to treat.” ● High success rate of surgery even after recurrence Looking at the spread of thyroid cancer, cancer cells begin to spread within the thyroid tissue. Then, the cancer cells break through the membrane surrounding the thyroid gland and spread to the lymph nodes around the thyroid gland (50-80%) or the lymph nodes near the neck (10-20%). The remaining 10% metastasize to the lungs, bones, soft tissue, brain, liver, etc. Depending on the extent of cancer progression, it is divided into stages 1 to 4, and the survival rate was investigated to be 90-95% for stage 1, 80-85% for stage 2, 70-75% for stage 3, and 40-45% for stage 4. Thyroid cancer can also recur after surgery. Most cases recur in the lymph nodes near the surgical site of the thyroid gland. Recurrences can also occur in the remaining thyroid tissue. If the contralateral thyroid gland is left, recurrences occur in the remaining side in about 5-10% of cases. In addition, cases where metastases occur to the mediastinum, lungs, or bones in the chest are also classified as recurrences. In cases where thyroid cancer recurs, it is effective to completely remove the affected area through surgery. Afterwards, high-dose radioactive iodine therapy or external radiation therapy is added. Recent advancements in surgical techniques have made surgery possible even when cancer cells have invaded the trachea, esophagus, major arteries leading from the heart, or major blood vessels in the chest. Director Jang said, “Even in cases where it has metastasized to the bones or lungs, the prognosis is good if it is removed surgically and nuclear medicine and radiation therapy are added.” ● Treatment of refractory thyroid cancer Refractory thyroid cancer is difficult to treat and is a general term for poorly differentiated cancer, undifferentiated cancer, and recurrent or metastatic cancer. Refractory thyroid cancer is difficult to treat with surgery and does not respond well to existing radioactive iodine therapy or thyroid hormone therapy. Director Jang said, “If the response to additional treatment is expected to be poor, it is considered refractory.” There is no definitive treatment for refractory thyroid cancer, and different methods may be selected depending on the individual situation. Nevertheless, the best treatment for cancer is complete resection. Director Jang emphasized, “Repeated surgery is difficult, but there is no more effective method. It is important for patients to have the will to be treated.” Director Jang said, “If new treatments such as targeted anticancer drugs are developed through future molecular biology research, it will be able to bring about more hopeful results.”