Like the treatment principles of other solid tumors, the surgical treatment of esophageal cancer should achieve accurate staging, reduce local recurrence, prolong patients’ survival and improve their quality of life through radical surgical resection. Therefore, when considering the surgical modality, it is more important to make a reasonable choice in combination with the current status of surgical treatment, in addition to the resection possibility of the tumor itself, in order to achieve the treatment purpose.
The value of debulking
Like the treatment principles of other solid tumors, the surgical treatment of esophageal cancer should achieve accurate staging, reduce local recurrence, prolong patients’ survival and improve their life quality through radical surgical resection. Therefore, when considering surgical methods, besides the resection possibility of the tumor itself, it is more important to make a reasonable choice in combination with the current status of surgical treatment in order to achieve the treatment purpose.
A lot of clinical studies have shown that the value of lymph node dissection for esophageal cancer is reflected in the following aspects.
1. The accuracy of surgical pathological staging is improved. Especially, the 7th edition of UICC (Union Internationale de Lutte Contre le Cancer) in 2009 proposed N grading according to the number of metastatic lymph nodes, so more than 12 lymph nodes must be cleared to ensure the accuracy of staging.
2. There is a more in-depth understanding of the lymphatic metastasis of esophageal cancer. The metastatic lymph node groups of thoracic esophageal cancer are the cervicothoracic junction laryngeal retrolateral nerve chain, upper, middle and lower esophageal parietal and cardia-left gastric artery-abdominal artery chain, which require systematic clearance of lymph nodes in these areas from both staging and radical treatment.
3. The radicality of surgery is improved, local recurrence is reduced after surgery, and the long-term survival rate of patients is improved. Comparing the results of lymph node dissection and conventional esophagectomy, it is easy to find that the local recurrence rate after two-field or three-field lymph node dissection is generally less than 20%, while it can be as high as 30%-40% after conventional surgery; the 5-year survival rate of patients after three-field dissection can reach 40%-50%, while it is rarely higher than 30% after conventional surgery.
Clearance focus
Lymphatic vessels within the submucosa of the esophagus travel longitudinally, whereas lymphatic vessels draining laterally to the paraesophageal lymph nodes originate in the intrinsic muscular layer, with little traffic between them.
The lymph node metastasis of early stage esophageal cancer invading the submucosa is seldom located near the tumor lesion, but more likely to appear in the lymph nodes of the laryngeal nerve chain at the cervicothoracic junction and the lymph nodes of the left cardia-gastric artery at the gastroesophageal junction, therefore, regardless of the T-stage of esophageal cancer, the above two areas are the focus of lymph node dissection.
Cleanup pathway
The lymph nodes in the upper paraesophageal and cervicothoracic junction cannot be cleared in the left thoracic approach due to the occlusion of the aortic arch and the left common carotid artery and subclavian artery. The triple incision of the right anterior thoracic approach also makes it difficult to completely remove the lymph nodes in the upper mediastinum, especially on the left side of the trachea, due to the limitation of the anterolateral chest incision.
In contrast, the right posterior external thoracic incision has the best exposure of the upper mediastinal lymph nodes, and the superior median incision also helps to completely remove the paracranial lymph nodes around the foot of the diaphragm, so the Ivor-Lewis or McKeown approach via the right posterior external thoracic incision is mostly recommended by domestic and foreign units performing systematic lymph node dissection.
In recent years, many units in China and abroad have begun to experiment with thoraco-laparoscopic or mediastinoscopic esophagectomy. The aim of minimally invasive surgery is to reduce the impact of surgical trauma on the functional status of the patient, and one of its principles is that it must achieve similar therapeutic results as open surgery. Although lumpectomy cannot achieve the same degree of lymph node dissection as open surgery, lumpectomy is generally performed through the right thoracic route, which facilitates the dissection of lymph nodes in the mediastinum, so the conversion of lumpectomy to lumpectomy can help improve the degree of lymph node dissection.
Scope of lymph node dissection
Clinical studies on lymph node dissection for esophageal cancer began in the 1980s, and the scope of surgery was expanded from the middle and lower mediastinum and upper abdomen (traditional two-field dissection) to the cervicothoracic junction of the upper mediastinum (expanded two-field dissection) and later to the neck (three-field dissection), during which there were many debates on the scope of dissection.
Although rigorous prospective randomized controlled clinical studies are still lacking, it is indisputable that the greater the extent of dissection, the better the surgical results, and the surgical risks increase, especially the higher incidence of cervical anastomotic fistula, laryngeal recurrent nerve injury and respiratory complications after three-field dissection, which affects the patients’ recovery and postoperative quality of life.
Therefore, the rational selection of lymph node dissection scope to ensure the efficacy and reduce the negative effects of surgery is a key issue to be solved.
In recent years, some studies on “selective three-field clearance” have been conducted at home and abroad to target patients with high risk of cervical lymph node metastasis and to avoid trauma caused by unnecessary expansion of surgery. Noguchi et al. tried to introduce the concept of “sentinel lymph nodes”, i.e., additional cervical debridement only for cases with intraoperative upper and middle mediastinal lymph node metastases; in recent years, we have performed selective three-field debridement under ultrasound guidance and achieved certain results. All these are new trends to ensure the radicality of surgery while reducing the risk of surgery and making the treatment more reasonable.
Impact on prognosis
Lymph node metastasis is an independent prognostic factor affecting the long-term survival of patients with esophageal cancer after surgery. The new staging of N-stage is reflected in the refinement of local lymph node metastasis into three grades of N1, N2 and N3 according to the number of metastases.
The results of our case group also showed that the 5-year survival rates of patients with different numbers of lymph node metastases differed significantly, with 48%, 32%, 12% and 0% for pN0, pN1, pN2 and pN3 patients, respectively; the survival rates of patients with no lymph node metastasis, single group of lymph node metastasis and two or more groups of lymph node metastasis also differed significantly, with 48%, 38% and 11%, respectively, and the 5-year survival rates of patients with lymph node metastasis in one field, two fields and three fields were extremely different. The 5-year survival rate of patients with lymph node metastasis was extremely significant (34.2% versus 12.1% versus 0, P < 0.001); multifactorial analysis showed that the number of metastatic lymph node groups and the number of fields were independent prognostic factors for patients, which indicated that the extent of lymph node metastasis better reflected the number of metastases than the number of metastases.
The extent of metastatic nodes better reflected the degree of tumor progression than the number of metastases.
Patients with single (32%), single group (38%), and single field (35%) lymph node metastases were still able to achieve satisfactory long-term survival, while patients with multiple groups or even multiple fields of lymph node involvement had difficulty in achieving satisfactory long-term outcome even with complete resection. The prognosis is extremely poor for those with metastases in the cervical, thoracic and abdominal fields.
In view of the fact that three-field clearance is the limit of esophageal cancer surgery, how to improve the accuracy of preoperative N-stage and carry out effective induction therapy on this basis, and perhaps to perform surgical resection after the tumor has obtained a descending stage, is the way out to improve the efficacy of locally progressive esophageal cancer.
In conclusion, lymph node dissection is an important tool in the surgical treatment of esophageal cancer. The newly published Guidelines for Standardized Diagnosis and Treatment of Esophageal Cancer in China suggests that the indications for surgery for squamous esophageal cancer of the thoracic segment should be those with no more than 6 lymph node metastases (N0~2); while in the new staging, stage IIIC or above disease is clearly listed as a contraindication to surgery, especially for those with multiple groups, multiple fields and multiple lymph node metastases (N3).
Meanwhile, the Guidelines clearly point out that lymph node dissection has improved staging accuracy, prolonged local control of tumor, and improved cure rate, but for locally advanced cases with extensive lymph node metastases, unlimited expansion of surgery is counterproductive. Selecting standardized and reasonable debulking according to the anatomical and tumor biological behavioral characteristics of lymphatic metastasis in esophageal cancer is the key to improve the efficacy of esophageal cancer.