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Endoscopic Treatment for Early Gastric Cancer

Endoscopic resection has been accepted as a curative modality for early gastric cancer (EGC). Since conventional endoscopic mucosal resection (EMR) has been introduced, many improvements in endoscopic accessories and techniques have been achieved. Recently, endoscopic submucosal dissection (ESD) using various electrosurgical knives has been performed for complete resection of EGC and enables complete resection of EGC, which is difficult to completely resect in the era of conventional EMR. Currently, ESD is accepted as the standard method for endoscopic resection of EGC in indicated cases. In this review, the history of endoscopic treatment for EGC, overall ESD procedures, and indications and clinical results of endoscopic treatment will be presented.


Introduction
Endoscopic resection has been accepted as a curative modality for early gastric cancer (EGC) in indication of complete resection without the risk of metastasis. Since conventional endoscopic mucosal resection (EMR) has been introduced from 1984, many improvements of endoscopic accessories and techniques have been achieved. (1) Recently, endoscopic submucosal dissection (ESD) using various electrosurgical knives has been performed for complete resection of EGC, and enables complete resection of EGC which had many technical difficulties in complete resection in the era of conventional EMR.
As the proportion of EGC has been increasing by early detection with national cancer screening program in Korea (biannual upper endoscopy or barium study for all population over age of 40), endoscopic treatment for EGC has been expanded with the progress of endoscopic technique and accessories. In this review, endoscopic resection for EGC would be presented as the history, indication, risk of lymph node metastasis and clinical results.

History of Endoscopic Resection for EGC
Since endoscopic resection with electrosurgical snare has been introduced for colorectal polyp in 1973, endoscopic resection has been performed for polypoid-type EGC as curative intent. In 1984, strip biopsy method has been developed for resection of flat-type EGC. In this method, the flat lesion is changed to polypoid lesion by submucosal injection of mixture of normal saline with diluted epinephrine, and resected by grasper forcep and electrosurgical snare through 2-channel endoscope. Although this method had advantages of easy technique, short procedure time and less complication, complete resection rate was around 50~70%, which was lower than expected for large-sized or depressed-type EGC. (2) In 1988, EMR-precutting method has been developed, in which after hypertonic saline with diluted epinephrine is injected to submucosal layer around the lesion, circumferential incision around the lesion with needle knife and final resection of the lesion is performed with electrosurgical snare. This method has enabled complete en-bloc resection rather than conventional EMR, but risk of perforation was higher during the circumferential incision, which necessitated higher expertise. Moreover, en-bloc complete resection was still difficult for large-sized or depressed-type EGC.
In 1992, EMR by the cap-fitted method (EMR-C) has been developed, in which en-bloc resection was performed with electrosurgical snare after suction of the lesion by cap-fitted endoscope.(3) Although this method was easier and safer than conventional EMR for en-bloc resection of small-sized EGC, enbloc complete resection was still impossible for larger-sized EGC than diameter of the cap. (4) To overcome the disadvantages of previous methods, ESD has been developed in late 1990's. In ESD, circumferential incision and direct dissection of submucosal layer of EGC has been possible with various knives, which has enabled en-bloc complete resection even in large-sized or depressed-type EGC. Various knives have been introduced for safe and complete ESD for EGC, and have different advantages/disadvantages according to the lesion. In present, insulation-tipped (IT), triangle-tipped (TT), flex, hook, fork, flush and splash knives are available for ESD.

Procedure of ESD
ESD is usually performed under sedation with intravenous midazolam or propofol. With a standard single-channel endoscope, thorough examination is mandatory for the evaluation of whole stomach including the target lesion. After the chromo-endoscopic observation with indigo carmine, marking dots 5 mm outside the tumor margin are made using a conventional needle knife with a forced 20 W coagulation current (VIO 300D; Erbe, Tübingen, Germany) or argon plasma coagulation. Then a mixture of normal saline and indigo carmine with diluted epinephrine (1 : 100,000) is injected into the submucosal layer along with the marking dots to make the submucosal cushion beneath the lesion. After a small initial incision is made with the needle knife, a circumferential mucosal incision is made around the marking spots, and the submucosal layer is dissected using various knives in 80 W endocut mode. Hemostasis is usually performed for bleeding spots or visible vessels with a coagrasper or argon plasma coagulation. After ESD, the patients is administered proton pump inhibitors intravenously at the day of procedure and then orally for four weeks for the healing of iatrogenic ulcer, pain control and prevention of perforation or post-procedural bleeding.

Selection of Knife
Knife is divided into blade-and tip-type according to resection *Defi nite indication by guideline; † Expanded indication; ‡ Surgery, but need for more consideration; § Surgery. m = mucosa; sm = submucosa.
circumferential incision and submucosal dissection, even in hemostasis of minor bleeding with coagulation current.
After hole-making with TT knife alone, circumferential incision around the lesion is performed with pull-method from distant part. In submucosal dissection, pull-method with diathermic disc is performed from distant part by step by step. Apart from IT knife, dissection with diathermic disc alone needs longer procedure time.
The risk of perforation in dead angle can be reduced by fitting transparent cap which enables direct vision of dissection.

Conclusions
ESD has been a curative treatment modality of EGC in selective indications. The complete resection rate, long-term disease-free results and survival has been comparable to surgical treatment with the progress of endoscopic technique and accessories. After