Thyroid nodules are common, with a detection rate of 3%-7% by palpation and up to 20%-76% by ultrasound at high rates.1 Most benign nodules can be observed and followed without specific treatment; the remaining thyroid nodules are eligible for local pressure symptoms, combined hyperthyroidism and ineffective medical treatment, retrosternal or mediastinal goiter, predisposition to malignancy, or combined risk factors for thyroid cancer. In recent years, with the development of minimally invasive techniques, ultrasound-guided percutaneous thermal ablation such as radiofrequency ablation (RFA), microwave ablation (MWA) and laser ablation (LA) have been gradually applied. The use of radiofrequency ablation (RFA), microwave ablation (MWA) and laser ablation (LA) for the treatment of thyroid nodules has been increasing. The effectiveness and safety of ultrasound-guided percutaneous thermal ablation has been demonstrated as an option for the non-surgical treatment of benign thyroid nodules, and the 2012 consensus of the Executive Committee of the Korean Society of Thyroid Radiology and the recent Italian consensus on radiofrequency ablation of thyroid nodules both oppose the use of this procedure for primary operable primary thyroid cancer. Some clinicians at home and abroad have explored the application of ultrasound-guided percutaneous thermal ablation in the initial treatment of thyroid tumors in recent years, and few relevant clinical studies have been reported; therefore, by reporting two cases of primary thyroid cancer treated by ultrasound-guided percutaneous thermal ablation admitted in October-November 2015 and reviewing the relevant literature, the author summarized the relevant experience to provide reference for clinicians. There are few reports on the application of thermal ablation technique to primary thyroid tumors, and the author identified 7 literature with more complete records, 6 reports in English and 1 report in Chinese, 2 of which are treatises and the other 5 are case reports, as shown in Table 1. Combining the reports of previous studies and the 2 cases in this paper, a total of 40 patients were included in the analysis, 1 case with follicular tumor on puncture cytopathology and 6 cases with Thy3 nodules (follicular lesions or follicular tumors)8, 1 medullary thyroid cancer (MTC), and the remaining 32 papillary thyroid cancer (PTC); 12 cases were treated with thermal ablation followed by surgery, and histopathological results were obtained in all cases. The histopathological results were obtained in all 12 cases; 37 of the 40 cases were unilateral lesions and the remaining 3 cases were bilateral lesions. It was confirmed by histopathology that tumor residual occurred in 9 cases after thermal ablation treatment, 1 case was follicular tumor, 1 case was follicular carcinoma, 1 case was MTC, and the remaining 6 cases were PTC, the incidence of tumor residual was 20.9% (9 43); the residual rate of lesions with tumor diameter >25px was 55.6% (59), while the residual rate of lesions with tumor diameter ≤25px was 11.8% (434) There was a significant difference between the two groups (p=0.011), and univariate regression analysis showed that the risk factors for tumor residual included tumor diameter >25px (OR=9.38, 95% CI: 1.75-50.22, p=0.009) and multiple lesions (OR=6.00, 95% CI: 1.12-32.14, p=0.036) (see Table 2); 5 of 12 cancer metastases in the cervical lymph nodes occurred in 5 of the operated patients, of which 5 cases were not mentioned in the literature as to whether lymph node metastases occurred, and the remaining 2 cases did not have cancer metastases, with an incidence of 41.7% of metastases remaining (512). 4. Discussion In 2012, the experts of the Executive Committee of the Korean Society of Thyroid Radiology have reached a consensus that radiofrequency ablation can be used for the treatment of benign thyroid nodules and inoperable recurrent thyroid cancer, but it is not recommended for follicular neoplasm (FN) or primary thyroid cancer.6 The recently published Italian Radiofrequency Ablation of Thyroid Nodules The consensus states that radiofrequency ablation is recommended for benign thyroid nodules meeting certain indications and for recurrent thyroid cancer where surgery is contraindicated and I131 therapy is not effective, whereas follicular neoplasm or primary thyroid cancer are not indications for radiofrequency ablation.7 Ultrasound-guided percutaneous thermal ablation is a new minimally invasive treatment technique that produces thermal coagulation necrosis of the localized lesion through a puncture device under real-time ultrasound monitoring. Depending on the principle and equipment of thermal ablation, it is divided into radiofrequency ablation, microwave ablation, and laser ablation.9 Because thermal ablation can effectively reduce the size of thyroid nodules, relieve nodule-related symptoms, and avoid surgical trauma,4, 5 it has been used in the treatment of benign solid nodules in several clinical centers internationally, especially in Korea and Italy. 6, the recommended indications include:1 benign thyroid nodules consistent with (1) the presence of local symptoms such as neck pain or discomfort, dyspnea, foreign body sensation and cough (self-measured by the patient using the visual analog scale 0-10 method), (2) affecting the appearance (appearance self-measurement rating: 1, no palpable mass; 2, palpable mass not affecting the appearance; 3, affecting the appearance when swallowing; 4, affecting the appearance) , (3) autonomous functional nodules combined with hyperthyroidism;2 recurrent thyroid cancer, where the patient is a contraindication to surgery or refuses surgery; it is also proposed that radiofrequency ablation is not recommended for thyroid follicular tumors and primary thyroid cancer. On this basis, in June 2015 Garberoglio R et al7 published the Italian version of the statement of indications for radiofrequency ablation of thyroid nodules, which reads as follows:1 Absolute indications: (1) non-functional benign nodules (volume greater than 20 ml) presenting local symptoms or affecting appearance, where surgery is contraindicated or refused, (2) autonomous functional nodules with hyperthyroidism or subclinical hyperthyroidism, where surgery (2) those with hyperthyroidism or subclinical hyperthyroidism for which surgery and radioactive iodine treatment are contraindicated or refused, (3) palliative treatment of recurrent thyroid cancer that is inoperable and for which radioactive iodine is ineffective;2 relative indications (most agree): non-functional benign nodules (volume less than 20 ml) with early local discomfort and rapid enlargement;3 relative indications (few agree): treatment of autonomous functional thyroid nodules (volume greater than 20 ml) in combination with low-dose radioactive iodine to improve local symptoms;4 20 ml) to improve local symptoms;4 Contraindications: (1) cystic thyroid nodules, where transdermal ethanol injection is preferred, and (2) primary thyroid cancer or follicular tumors, where surgery is the standard treatment. Currently, there is a lack of unified and standardized opinion on the treatment of thermal ablation of thyroid nodules in China, and some doctors have used thermal ablation technique as a treatment for primary thyroid cancer in addition to benign nodules. Based on the existing research reports, I believe that thermal ablation is not yet mature for primary thyroid cancer, and the following issues need to be considered: a. Local ablation was first used as palliative treatment for inoperable and recurrent malignant tumors, and even now it is mainly used for some primary liver cancer and inoperable primary kidney cancer under strict indications. However, the different organ characteristics and its relationship with surrounding tissues dictate that this tool cannot be fully replicated in the treatment of thyroid cancer. In the case of primary liver cancer, which is currently the subject of many treatment studies, for example, the energy range of RFA needs to cover the entire tumor margin, or even establish a safety margin (5-10 mm), and the indications or special isolation measures need to be restricted for lesions with close relationship to surrounding organs and large blood vessels. The size of the thyroid gland differs greatly from that of the liver and kidney, and the establishment of a safety margin is severely restricted by the surrounding trachea, laryngeal return, arteries and parietal glands, etc. This problem is even more prominent for those whose primary foci are close to these tissues and organs. If the operator operates with reference to this safety margin, there will be huge surgical complications. Secondly, papillary thyroid carcinoma is multifocal in nature, which increases the possibility of residuals on the one hand, and repeated ablation operations when dealing with multiple foci on the other hand are more likely to cause increased complications. In order to control the ablation complications, the rational choice is to reduce the single power and safety margin; for benign nodules, the treatment purpose can be accomplished as long as the nodules shrink, but from the perspective of thyroid cancer radical treatment, it causes unavoidable residual risk. In the two cases reported by the author, the incomplete treatment of thermal ablation led to residual lesions, and a review of the existing case reports shows that the incidence of residual tumor after thermal ablation is as high as 20.9%, among which all nodules above 25px are residual, and the incidence of nodules ≤25px is 14.3%. The residuals may be caused by insufficient scope, dose and time of thermal ablation. The author also noted that some literature reported the safety of radiofrequency ablation for papillary carcinoma, but the follow-up cases listed in the literature have no ethical statement and the follow-up time is only 3-18 months, which is far from enough for determining the recurrence of metastasis in thyroid cancer. Second, thermal ablation has serious shortcomings in the treatment of metastatic thyroid cancer lymph nodes in the neck. It has been reported that suspicious metastatic lymph nodes can be detected by ultrasound and confirmed by puncture and then treated therapeutically.10 First, the common metastatic site of papillary thyroid cancer is the VI area of the neck, and its lymph nodes are distributed in the anterior larynx, anterior trachea and tracheoesophageal groove, among which the lymph node metastasis in the tracheoesophageal groove cannot be treated by ablation. The sensitivity of ultrasound and neck CT in identifying lymph node metastases in the neck is 51% and 62%, respectively.11 The incidence of clinically negative neck lymph node metastases (cN0) in papillary thyroid carcinoma ranges from 25% to 63.83%.12 Even papillary thyroid microcarcinoma (PTMC) with cN0 has a low sensitivity. The incidence of lymph node metastasis in the neck of papillary thyroid microcarcinoma (PTMC) with cN0 is as high as 42.4%.22 If these patients choose thermal ablation to treat lymph node metastasis, it is easy to be left behind. Even radiotherapy sensitive head and neck tumors such as nasopharyngeal carcinoma need to focus on irradiation field covering lymph node distribution and drainage area, while thermal ablation technique only achieves selective elimination of some lymph node metastases. Third, follicular carcinoma is mainly characterized by tumor envelope and vascular invasion, which is more aggressive than papillary thyroid carcinoma and has increased incidence of distant metastasis, and thermal ablation technique is not applicable to the management of this type of tumor. The malignancy rate of follicular tumors with fine needle aspiration cytopathology is 15-30%.13 The 2015 American Thyroid Association (ATA) guidelines for the treatment of adult thyroid nodules and differentiated thyroid cancer14 state that follicular tumors or suspicious follicular tumors may be treated without molecular testing or when molecular testing cannot determine benign malignancy. Dobrinja C et al15 confirmed that RFA should not be used as the first-line treatment for Thy3 nodules on perforated cytopathology. Lee CU et al16 reported a patient with follicular tumor by puncture, and after two years of follow-up after RFA treatment, the original lesion recurred and a new mass appeared in the broad neck muscle, and both the recurrent lesion and the broad neck muscle mass were confirmed to be papillary carcinoma after surgical resection. Studies of RFA treatment of hepatocellular carcinoma have shown that incomplete RFA can accelerate the evolution of residual tumor cells leading to tumor regrowth.17 Park KW et al18 reported tumor regrowth after RFA treatment of inoperable recurrent thyroid cancer. whether RFA may promote follicular cell tumor transformation or whether incomplete RFA treatment leads to accelerated evolution of residual cancer cells requires further Further studies are needed to confirm this. The risk of residual cancer and lymph node metastases in primary thyroid tumors treated with thermal ablation is high, and it cannot be used as a routine treatment for operable primary thyroid cancer or follicular tumors yet.