2108 cases of thyroid cancer cervical lymph node dissection or not

Clinical and pathological data from 2108 patients with thyroid cancer, who were initially diagnosed and treated surgically, were collected from the Department of Thyroid Surgery. Among them,There were 1001 cases underwent open operation with total thyroidectomy + central lymph node dissection, meanwhile 1107 cases were treated with neck lateral lymph node dissection at the same time.The overall metastasis rate of all patients was 57.23%. Even the lymph node metastasis of PTMC was as high as 48.97%. When the mass rose above 2cm, the proportion of metastasis increased to 77.22%. With the increase of tumor diameter, the metastasis of cervical lymph nodes ranged from 22.54% to 73.33%, which showed positive correlation.When the diameter of the tumor reached T1c level, the metastasis of the cervical lymph nodes was 56.91%, and the number of metastatic cases above T1c level accounted for 69.96% of the total metastatic cases. It is recommended that initial treatment should comprise at least total thyroidectomy + central lymph node dissection in China, to avoid the risks associated with secondary surgery and effects on patient quality of life.When the tumor diameter exceeds 1cm, the risk of cervical lymph node metastasis is high, we recommended the lateral lymph node dissection.


Introduction
In the past 30 years, the incidence of thyroid cancer has been increasing annually worldwide, with the incidence in China also rising. In 2012, the number of new cases and deaths from thyroid cancer in China accounted for 15.6% and 13.8%, respectively, of the global total. It is estimated that by 2019, thyroid cancer will become the third most common malignancy in women in the United States, leading to medical expenditure of approximately $19-21 billion, representing a heavy economic burden on both society and individuals. 1 Differentiated thyroid carcinoma accounts for 80%-90% of thyroid cancer incidence and the most common metastasis is to the cervical lymph nodes, which seriously influences patient prognosis. Therefore, effective and appropriate surgical treatment of differentiated thyroid carcinoma is of great clinical significance. Total thyroidectomy and lobectomy remain the main primary surgical interventions for thyroid carcinoma. To date, there has been no large sample randomized controlled clinical trial to compare these two methods, hence their relative efficacy remains controversial and comparative studies have relied mainly on retrospective analyses. 2 This indicates that although papillary thyroid carcinoma(PTC) progress is slow, the ability and tendency to metastasize to lymph nodes and even distant organs are consistent with other malignancies. In generally, it is unscientific to classify malignant tumors based on tumor size. The invasiveness and distant metastatic ability of tumors are derived from the evolution of the tumor genome. 3,4 There are still different opinions on whether to perform preventive lateral neck lymph node dissection. The focus of debate is on the following aspects: Preventive lateral neck lymph node dissection needs to expand neck incision and affect appearance; Lateral neck lymph node dissection can cause shoulder syndrome, which seriously affects the patient's quality of life; Differentiated thyroid cancer is slow to develop, as long as it is closely followed by diagnosis, allowing treatment when suspicious lymph nodes are found. 5,6 We collected clinical and pathological data from 2108 patients undergoing treatment at

Results
All patients were treated directly after discovery of the lesion, without any observation period. Cases included 416 males and 1692 females, and were 13-79 years old, with 285 cases aged ≤ 35 years ( Table 1).
The pathological subtypes present among the 552 cases of PTC were classical (n = 537),  In all patients with positive lymph nodes in the central area, 62.88% of the patients had cervical metastasis. Only 6.78% of patients had jump metastasis, that is, the central lymph nodes were negative, and cervical lymph node metastasis occurred, of which T1c patients accounted for 30.67%, T1c and above patients accounted for 78.55% (Table 8).
Of the patients with T1a, 57.04% did not have metastasis. In T1b, there was no metastasis in 31.71% of lymph nodes, 30.57% had only central lymph node metastasis, and 32.57% had metastasis in Central and neck regions. In T1c patients, 50.41% of patients had metastasis. In T2 patients, the metastasis rate was 61.04%, and in T3 patients, it was as high as 53.3% (Table 9).
In addition, we enumerated the number of cases of surgery for thyroid cancer at our hospital from 2009-2018 and the results demonstrate that the number of cases generally rose annually by 4.72%-18.16% ( Figure 2).

Discussion
According to the results of the SEER database of the National Cancer Center of the United States, the incidence of both PTC < 1.0 cm and thyroid cancers 1.0-4.0 cm increased from 1980 to 2010, especially among highly educated groups. 7 Statistical data from the United States and South Korea show an increase in the incidence of thyroid cancer. 8 Further, the results of surveys in Denmark, Finland, Israel, Japan, Spain, and Switzerland also demonstrate increases in thyroid cancer incidence, which is mainly PTC, with significant sex differences in the relative extent of the rise. This phenomenon cannot be fully explained by improvements in the sensitivity of testing methods, nor increased awareness among doctors and patients of screening. 9 Scholars from other countries have actively researched the risk factors associated with thyroid cancer, and found that autoimmune disorders, ionizing radiation, iodine intake, estrogen, environmental endocrine disruptors, negative psychosocial factors, and heredity may contribute to increases in thyroid cancer incidence. 10,11 From 1984 to 2010, the incidence of differentiated thyroid carcinoma in the United States increased, with tumors of diameter ≤ 0.5 rising by 5.09%, while those of 0. According to our clinical and pathological data, as the diameter of the mass increases, the proportion of lymph node metastasis increases, from 44.68% to 77.53%. The proportion of micropapillary carcinoma ≤ 1 was 47.10%, and the rate of lymph node metastasis was 46.92%, which did not mean that the risk of microcarcinoma was low. Lymph node metastasis is also an indicator of malignancy. With the passage of time, the tumor size, the proportion and the number of lymph node metastasis will further increase, leading to the disease progression, the difficulty and risk of surgery, and the risk of recurrence and metastasis gradually increased. When the mass rises above 2cm, the lymph node metastasis ratio rises to 77.53%, indicating that thyroid papillary carcinoma is progressing, the malignant degree and the disdifferentiation increases, although there is no way to evaluate and predict it. The bilateral tumor metastasis rate is 65.27%, the recurrent cancer metastasis rate is 72.21%, the tumor breakthrough membrane metastasis rate is 67.08%, and the metastasis rate is higher than the average metastasis rate. The analysis is statistically significant.
When combined with high risk factors, such as bilateral lesions, multiple lesions and tumor rupture membranes, the lymph node metastasis rate will increase significantly. 17  It is recommended to keep the sternocleidomastoid, the internal jugular vein and the accessory nerve, and try to keep the cervical plexus neurocutaneous branch. At present, the modified radical neck dissection (MRND) is the most commonly used procedure for both thorough surgery and preservation of the body function. Lymph node metastasis of thyroid papillary carcinoma is common to the ipsilateral side, and it is transferred along the lymphatic drainage path. The lymphatic metastasis is usually first to the paratracheal lymph node, and then drained to the jugular vein lymph node (levelⅡ-Ⅳ) and the posterior cervical lymph nodes (levelⅤ), or down the trachea to the upper mediastinum. The most common site in the 6th district, followed by the neck Ⅲ,Ⅳ,Ⅱ,Ⅴlevel, and the lymph node metastasis of papillary thyroid carcinoma is mainly metastasis.
At present, surgical treatment of cervical lymph node metastasis of papillary thyroid carcinoma is recommended for the treatment of cervical lymph node dissection.
Prophylactic dissection is not recommended. The occult metastasis of cervical lymph nodes does not reduce the survival rate of patients, so prophylactic cervical lymph node dissection is not recommended in patients with cN0.
For patients with cN1, lymph node metastasis is an independent risk factor for the survival of patients with > 45-year-old papillary thyroid carcinoma. 20,21 levelⅡ-Ⅳis the main area of thyroid lymphatic drainage, and levelⅢ,Ⅳis the most common lymph node metastasis.
Domestic experts agree that levelⅡa,Ⅲ,Ⅳ,Ⅴb is the standard range of cervical lymph node dissection. 22 It is recommended that patients with cervical lymph node metastasis confirmed by preoperative evaluation or intraoperative frozen pathological examination receive cervical lymph node dissection, but preventive cervical lymph node dissection is not recommended. 23 Reoperation will increase the complications of surgery, and it will lead to recurrence of disease after thyroid cancer surgery, and even affect survival. At the same time, as the number of operations increases, the degree of tumor dedifferentiation will increase, and the difficulty and risk of surgery will increase. It is impossible to completely remove the surgery again, so that the patient who can be cured can lose the opportunity to cure. 24,25 Thyroidectomy can lead to complications, primarily parathyroid injury (3%-5%) and recurrent laryngeal nerve injury (1%-5%). It is accepted that patients who undergo total or partial thyroidectomy must use thyroxine replacement, or even suppression, therapy for the rest of their lives. 26,27 Data from our hospital related to hypocalcemia, hoarseness, and sensory dysfunction of the shoulder after thyroid surgery currently undergoing statistical analysis and will be presented in future reports. The pathological characteristics of PTC mean that analysis of the influence of surgical approach on survival and prognosis will be a long-term project, and we will continue to analyze follow-up data for these patients. Only a small number of patients were found to have BRAF gene mutations in our study, as there is no comprehensive promotion of genetic testing in our hospital, hence not all patients were evaluated.
According to the CTA, endocrine inhibition therapy is essential, regardless of surgical approach. Hence, long-term endocrine suppression therapy was required for all patients with PTC, including those who underwent lobectomy + central lymph node dissection.
Radioactive I 131 therapy is also an important part of comprehensive treatment of thyroid cancer. 28,29 All patients with lymph node metastasis, whether in the central or cervical region, were treated with I 131 administered at doses of 80-130 mCi, according to risk stratification assessment, with additional rounds of treatment if needed, based on the results of follow-up observation.
The method of treatment of thyroid cancer is influenced not only by surgeons, but also by nuclear medicine, imaging, and other clinicians, and even by health insurance companies.
outcomes for patients with thyroid carcinoma. This is because such an approach facilitates more accurate surgery, and individualized treatment, as well as allowing collection of data on national trends in this disease. The authors consider that surgeons should fully embrace the principles of tumor prevention and treatment, and be mindful that thyroid cancer is a malignant tumor; hence, the scope of treatment should not be reduced unnecessarily, to avoid the need for reoperation several years later. Therefore, it is necessary to assess patients, according to current scientific knowledge, to make a comprehensive judgment of the safety of surgery, the willingness of the patient, and medical resources available, together with the national considerations and regional factors in China, and the degree of acceptance of the operation and possible secondary surgery by the patient. Together, this information can inform implementation of rational diagnosis and treatment plans.

Declarations
The data from our department inform several important points. lesions,and tumor breakthrough membranes, tumors were highly aggressive, suggesting that priority should be given to total central thyroidectomy lymph node dissection.
Postoperative complications and long-term follow-up data will be reported in the future. 4.
There is no need to prevent cervical lymph node clearance, but when the mass reaches         Table 9 The diameter and metastasis of cervical lymph node.
cervical Cases 0-0 0-1 1-0 1-1  Figure 2 Numbers of cases of thyroid cancer treated at our hospital in the past 9 years.