Although thyroid cancer is a rare type of cancer, its frequency has been increasing in recent years. Women are about 3 times more likely to develop thyroid cancer than men. The risk is higher also in patients who received radiotherapy to the neck and those with a family history of thyroid cancer. Thyroid cancers are histologically divided into four. The most common type is papillary cancer (about 80%) and follicular cancer (about 10%). Since these cancers are very slow, they are also described as “well differentiated“ because even in patients with metastases, survival is very long. Twenty-year survival rates were generally reported as 98-99% in papillary cancer and 80-90% in follicular cancer. The rarely seen medullary cancer and anaplastic cancer of the thyroid have a rapid course and survival is significantly shorter. Therefore they are called "badly differentiated". The estimated survival rates are 60-70% in medullary cancer in 10 years and only 10% in anaplastic cancer in 5 years.
How is it diagnosed?
Thyroid cancers can sometimes be felt as a nodule during the physical examination. Sometimes they may cause neck pain or hoarseness. However, most thyroid cancers are detected incidentally during the neck ultrasound performed for goiter or other reasons. Since thyroid ultrasound has been used more and more frequently thyroid cancers can be detected at an earlier stage than before. Although most of the thyroid nodules seen on ultrasound are benign, some ultrasound features may increase the likelihood of a nodule being cancerous. These include large size, irregularity of the edges, dark/grey color, excess of vascularization and areas of calcification in the nodule. Fine-needle aspiration biopsy (FNAB) should be performed if the ultrasound appearance of the nodule is considered suspicious. With this procedure performed under ultrasound guidance and under local anesthesia, it can be understood whether the nodule is benign or cancerous. If FNAB does not yield a definitive result, the patient should undergo another biopsy in several weeks. The second biopsy can be performed with the FNAB in combination with the trucut method, and in most of these patients, a definitive diagnosis can be achieved and unnecessary thyroid surgery can be avoided.
How is it treated?
If needle biopsy of the suspected thyroid nodule yields cancer, the classical treatment is the surgical removal of the entire thyroid gland and then radioactive iodine (RAI) administration. However, , approximately 80-85% of thyroid papillary cancers are considered to be low-risk papillary microcarcinomas and it is currently believed that systematical thyroidectomy and RAI are unnecessarily aggressive in these very slow-growing tumors. In fact, some researchers suggest that such patients may be followed up without treatment; In a study conducted in Japan, 1465 low-risk thyroid papillary cancer patients were followed up without treatment for a mean of 5 years, and only 5% of them turned into invasive cancer and only 2% developed lymph node metastasis. In papillary cancers, sometimes only a portion of the thyroid can be removed, but this procedure is usually not preferred by the surgeons.
Today, because of the widespread use of ultrasonography and FNAB, such papillary microcarcinomas are more and more commonly diagnosed. In these cancers, also known as papillary microcarcinoma, the tumor is within the thyroid gland, less than 1.5 cm in diameter and not spread to the surrounding lymph nodes. In such patients, 20-year survival was reported to be 99%. Therefore, in this patient group, it is currently questioned whether aggressive treatment methods such as surgery + radiotherapy are really strictly necessary. In these small papillary cancers, percutaneous thermal ablation methods such as radiofrequency, microwave and cryoablation are also an ideal option. However, although the short-term results of these methods are very good, their long-term results are not yet very-well known.
If the cancer recurs in the neck after thyroid surgery, re-surgery can be performed, although it is technically more challenging than the first operation. If the patient does not want surgery or is not eligible for surgery, ultrasound-guided alcohol ablation or thermal ablation methods such as laser, radiofrequency and microwave can be applied. Several studies have shown that these ablation methods can provide long-term local tumor control in such patients.
Although rare, thyroid cancers may sometimes metastasize to distant organs such as liver, lung and bones. In such cases, interventional oncologic therapies such as percutaneous ablation and chemoembolization may also be used besides the conventional RAI and chemotherapy.
Interventional oncology in cancer management
Prof Saim Yilmaz, MD