An outlook on the lymph nodes dissection during the pancreatectomy for pancreatic cancer

Pancreatic cancer is likely to be one of the most highly lethal diseases in the world.^{1, 2} Radical pancreatectomy with adjuvant chemotherapy is a curative treatment for pancreatic cancer.² Lymphadenectomy is an indispensable procedure in radical resection for pancreatic cancer. It is obvious that lymph node dissection is essential. According to the eight edition of the American Joint Committee on Cancer (AJCC) tumor node metastasis (TNM) staging system, the number of positive lymph nodes (PLNs) is related to the prognosis of the patients.³ Moreover, a standard lymphadenectomy reduces the incidence of local lymph node recurrence.^{4, 5} However, in some cases, the current guidelines or consensus cannot be satisfied in clinical practice. Thus, in this brief literature review, we summarize the current status of lymph nodes dissection in pancreatectomy while focusing on the further development of research.

The AJCC TNM staging system is the most worldwide used system that provides us a relatively accurate prognosis of the patients. The latest version is the eight edition of the TNM staging system.³ The main revision to the seventh edition is the modification of the N status in the system. Previously, in the seventh edition, the N status was separated into N0/N1 depending on whether regional metastatic lymph nodes were found in the operation. The impact of the number of PLNs on the prognosis was ignored. Currently, in the eight edition, the N status is divided into N0/N1/N2 based on the number of PLNs. The patients without lymph node metastasis are stated in the N0 stage. The patients with four or more PLNs are classified into the N2 stage, which implied poor survival. The rest are in the N1 stage whose PLNs are less than four.

In order to acquire accurate PLNs, a certain number of lymph nodes should be harvested. The optimal lymphadenectomy was disputed until a consensus statement on the extent of lymphadenectomy for pancreatectomy was published by the International Study Group on Pancreatic Surgery (ISGPS) in 2014.⁴ In this statement, the study group has affirmed the extent of lymph node dissection for the pancreatectomy. Based on the nomenclature for nodal stations of the Japanese Pancreas Society,⁶ a standard lymphadenectomy should include lymph node stations 5, 6, 8a, 12b1, 12b2, 12c, 13a, 13b, 14a right lateral side, 14b right lateral side, 17a, and 17b during the pancreatoduodenectomy (PD), while a standard lymphadenectomy during the distal pancreatectomy should include lymph node stations 10, 11 and 18 for the tumor located in the body and tail of the pancreas. Furthermore, the minimal number of examined lymph nodes (MNELN) for the PD was considered to be at least 15. With the increase of the number of regional lymph nodes retrieved, the accuracy of PLNs raised up.⁷

Except for the number of PLNs and the number of examined lymph nodes, the lymph node ratio is another important factor of survival prediction. In many former researches,^8-11 the lymph node ratio that referred to the number of PLNs involved to the number of examined lymph nodes was considered as an independent risk factor of patients’ disease-free survival and overall survival. However, among the number of PLNs, the number of examined lymph nodes, and the lymph node ratio, only the first one is mentioned in the TNM staging system.

Thus, the accuracy of the N status in the eight edition TNM staging system is totally dependent on the exact number of PLNs. Moreover, the number of regional lymph nodes retrieved determines the quality of lymph node dissection. Nevertheless, is optimal lymphadenectomy easy to be achieved in clinical practice? As the predictive factors, is the number of PLNs more significant than the lymph node ratio in the survival prediction? Is the current eight edition TNM staging system good enough to satisfy all the clinical conditions? All these problems need to be solved.

The “optimal” or “ideal” lymphadenectomy should be defined as a method of acquiring the adequate number of PLNs with little trauma during the dissection and reducing the potential postoperative lymph node recurrence. The “optimal” lymphadenectomy should have characteristics listed as below.

The lymph nodes dissection is an essential procedure in the radical pancreatectomy. At present, under the guidance of many guidelines and consensus, lymph node dissection has gradually been standardized. However, there are still some deficiencies that can be overcome stepwise. We are looking forwards to achieving an “optimal” lymphadenectomy in the future.

The authors have no conflict of interest to declare.