What Is Minimally Invasive Surgery for Patients with Gastric Cancer?

Objective : Minimally invasive gastrectomy is performed worldwide because it confers less stress and pain for patients with gastric cancer. Recently, other types of minimally invasive gastrectomy, which include robotic gastrectomy, have also been developed. In this paper, we will review the history, current status, and future prospects of minimally invasive gastrectomy. Methods : We overviewed gastric cancer and reviewed the outcomes of previous clinical trials. In addition, we present our newly developed technique of minimally invasive gastrectomy, especially for anastomosis. Results : Previous clinical trials showed that minimally invasive gastrectomy was similar or superior to open gastrectomy in terms of short-term results, while minimally invasive gastrectomy was not superior to open gastrectomy in terms of long-term survival. Many studies have reported that postoperative complications could induce cancer recurrence; hence, we hypothesize that the survival of patients who underwent minimally invasive gastrectomy will be better than that of patients who underwent open gastrectomy. An intracorporeal anastomosis might help decrease the incidence of postoperative complication because it can shorten the length of surgical incisions. However, this procedure requires experienced skilled surgeons. Conclusion : The surgical system of minimally invasive gastrectomy, including robotic gastrectomy, has dramatically improved. Although there are challenges that need to be addressed, we believe that using more advanced technology or equipment will make minimally invasive gastrectomy the standard treatment for gastric cancer in the future.


Introduction
Minimally invasive surgery for gastric cancer is preferred worldwide because it confers less pain and better cosmetic results, thereby reducing patientsʼ perioperative stress. Previous and retrospective analyses regarding minimally invasive gastrectomy focused on postoperative outcomes such as quality of life, nutritional status, and longterm survival 1)-3) . Most of these studies showed that minimally invasive surgery had similar or superior outcomes to open surgeries. However, only few randomized control trials have compared minimally invasive gastrectomy with open gastrectomy. In the real world, with improved diagnostic systems and surgical equipment, the use of laparoscopic gastrectomy for gastric cancer is increasing, particularly in East Asian countries 4) .
Recently, many procedures, including not only laparoscopic surgery but also robotic, reduced-port, and needlescopic surgeries, have been recognized as minimally invasive surgeries for gastric cancer 5) 6) . In addition, the anastomotic procedure has been developed during this decade, and the socalled intracorporeal anastomosis has become available. Currently, various types of minimally invasive gastrectomy are available, and the definition of minimally invasive gastrectomy has become 474 Mini Reviews Juntendo Medical Journal 2019. 65 (5), 474-477 obscure.
In this article, we reviewed the pathology, epidemiology, and treatment of gastric cancer. Moreover, we reviewed the history and current status of minimally invasive surgery for gastric cancer. In addition, we will discuss the future prospects and challenges of minimally invasive surgery for gastric cancer.

Pathology of gastric cancer
Gastric cancer is thought to occur when mucosal cells lining the inside of the stomach wall become cancerous and proliferate chaotically. Gastric adenocarcinoma is histologically divided into three types as follows: papillary, tubular, and poorly differentiated. As the cancer grows, it gradually progresses outward to the submucosa, proper muscle layer, and serosa. In gastric cancer, tumor cells may travel in the lymphatic or blood flow, and metastasis could occur when these cells infiltrate and proliferate in distant organs. Peritoneal dissemination is frequently detected in advanced gastric cancer, in which cancer cells are scattered beyond the serous membrane in the abdomen. Scirrhous type of gastric cancer spreads into the gastrointestinal musculature, making the stomach wall hard and thick, and its early diagnosis is difficult. The typical symptoms of gastric cancer are epigastric pain and discomfort, heartburn, nausea, and loss of appetite. Sometimes, cancer-associated anemia or bloody stool may trigger its detection. However, these symptoms may also occur from gastritis and gastric ulcers. Early gastric cancer is often detected during endoscopic examinations for medical checkups or for evaluating symptoms of other diseases.

Epidemiology
Gastric cancer is the fourth most common cancer worldwide. In general, the incidence is higher in East Asia and lower in Western countries. Compared to the mortality in colorectal or lung cancer, the mortality in gastric cancer has been decreasing in North America, Europe, and East Asia (Japan, China, and Korea) since the middle of the 20th century because of the rapid decline in the incidence of Helicobacter pylori infections 7) . Currently, 47,000 people die of gastric cancer annually in Japan. In these patients, peritoneal recurrence was the most predominant cause of death, which accounted for 44.3% of the mortality cases, based on the nationwide registry of the Japanese Gastric Cancer Association 7) 8) .

Staging
The tumor-node-metastasis (TNM) classification of the Union for International Cancer Control and American Joint Committee on Cancer is the global standard for determining the degree of tumor progression 9) . Gastric cancer stage is defined by the depth of the local tumor and whether it has metastasized to a lymph node and/or other organs. The clinical stage of the disease is determined after examination via endoscopy, computed tomography, staging laparoscopy, and positron emission tomography 10) .

Treatment strategy of gastric cancer
Treatments for gastric cancer include endoscopic resection, surgery, medication (mainly chemotherapy), and palliative radiation therapy. The fifth edition of the JGCA treatment guidelines is used as reference for applying the appropriate treatment strategy for each patient.

Surgical resection of gastric cancer
The extent of resection of the stomach should be determined on the basis of both the tumor location and the cancer stage. The types of gastric resection include total, distal, pylorus-preserving, and proximal gastrectomies. The first open distal gastrectomy (ODG) was performed by Billroth, an Austrian surgeon, in 1881.

Advancements in laparoscopic gastrectomy
The worldʼs first laparoscopic distal gastrectomy was performed by the Japanese surgeon Kitano in 1991. The first robotic gastrectomy was performed by Hashizume in 2003 11) .
In laparoscopic surgery, surgeons inflate the abdominal cavity with carbon dioxide gas and operate using forceps inserted through a small 3-to 10-mm-wide incision in the abdominal wall. During laparoscopic procedures, a camera allows surgeons to view images of the abdominal cavity on a video monitor 12) .
Previously, gastroduodenal, gastrojejunal, esophagojejunal, and jejunal-jejunal anastomoses were performed via mini-laparotomy (approximately 6 cm in length) in the epigastric area after gastrectomy. Currently, these anastomoses can be performed under a laparoscopic procedure, known as intracorporeal anastomosis 12) . Improvements of the linear stapler, circular stapler, and sutures allowed surgeons to perform anastomosis regardless of the patientʼs physique. Thus, mini-laparotomy has become unnecessary, and the incision length has been shortened; however, stapler handling and suturing requires an experienced skill. We reported the usefulness of intracorporeal reconstruction using the hemi-double stapling technique with a transorally inserted anvil for esophagojejunostomy 13) and the augmented rectangle technique for Billroth I anastomosis 14) . Both techniques are an entirely intracorporeal reconstruction.

Other new types of minimally invasive gastrectomy
Omori et al. reported the feasibility of singleincision laparoscopic surgery 6) , developed to reduce the invasiveness of laparoscopy. Furthermore, Kanehira et al. examined the viability of using needle forceps for gastrectomy 5) .
Robotic systems are making it increasingly possible to perform surgery with a natural sense of operation and high freedom of movement, even in the arthroscopic view. This is achieved by mounting a high-resolution 3-dimensional camera and EndoWrist with 7°of motion. Currently, the da Vinci surgical system is used in most robotic surgeries globally. Robotic gastrectomy for patients with gastric cancer became a reimbursable treatment according to the Japanese medical insurance system in April 2018 15) . With robotic gastrectomy, the challenge of postoperative pancreatic fistula as an adverse outcome of laparoscopic distal gastrectomy 16) can potentially be overcome. We expect that the advantage will be proven in future studies.

Why is minimally invasive surgery needed?
A South Korean randomized control trial showed that laparoscopy-assisted distal gastrectomy (LADG) had benefits over ODG in quality-of-life assessment 17) . The Stomach Cancer Study Group of the Japan Clinical Oncology Group (JCOG) has gathered the following evidence for laparoscopic gastrectomy. JCOG 0703, a multicenter phase II trial, confirmed the safety of LADG for early gastric cancer. JCOG 0912, a randomized phase III trial, confirmed that LADG was no worse than ODG with regard to relapse-free survival 18) . Thus, for laparoscopic distal gastrectomy, no inferiority for survival was proved. Meanwhile, regarding laparoscopic proximal and total gastrectomy, a clinical trial for safety is now being performed as JCOG 1401 19) . However, the superiority of minimally invasive surgery to open gastrectomy in terms of survival has not been shown yet.
We believe that laparoscopic gastrectomy has many advantages, including small incision size, which is related to less postoperative pain and blood loss, and improved operability regardless of patient physique. Furthermore, minimal invasiveness leads to better postoperative appearance, increased food intake, and earlier discharge from care, thus reducing the patientʼs perioperative stress. Moreover, owing to lesser preoperative loss of muscle mass and overall weight in minimally invasive laparoscopic surgery than in open surgery, patientsʼ nutritional statuses might improve and their survival may be lengthened 3) .
In contrast, postoperative complications have been reported to develop within 30 days, particularly abdominal infections, such as pancreatic fistula of Clavien-Dindo grade ≥II, were related to poor survival outcomes 20) and postoperative malnutrition 21) . Thus, it is important to ensure good patient nutrition and avoid postoperative complications to reap the benefits of minimally invasive surgery.

Summary
In this paper, we present the overview of gastric cancer and the history, current status, and future prospects of minimally invasive gastrectomy. Although there are challenges that need to be addressed, we believe that using more advanced technology or equipment will make minimally invasive gastrectomy the standard treatment for gastric cancer in the future.