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Endoscopic Mucosal Resection and Submucosal Dissection
Advances in endoscopic techniques have permitted endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD) to be used as curative therapies for select early gastric cancers (EGCs). This technique has been used widely for intestinal-type cancers in Japan and South Korea, where studies have shown that only 3.5% of patients with EGCs smaller than 2 to 3 cm have lymph node involvement, making these lesions amenable to local therapy. Lesions larger than 4.5 cm have a greater than 50% chance of spread into the submucosa, are associated with “positive” nodes, and are therefore less likely to be endoscopically resectable.361
The following criteria have been suggested for EMR in gastric cancer: (1) the cancer is located in the mucosa and the lymph nodes are not involved, as indicated by EUS examination; (2) the maximum size of the tumor is less than 2 cm when the lesion is slightly elevated (type IIa) and less than 1 cm when the tumor is flat or slightly depressed (type IIb or IIc) without an ulcer scar; (3) there is no evidence of multiple gastric cancers or simultaneous abdominal cancers; and (4) the cancer is of the intestinal type.362 Despite these guidelines, it is generally not possible to remove lesions larger than 1.5 to 2.0 cm en bloc by EMR, and piecemeal removal of EGC is associated with decreased rates of curative resection.363
ESD is a technique developed in Japan and permits en bloc resection of larger EGCs, as well as selected tumors with submucosal invasion. With ESD, submucosal injection is performed, followed by the use of endoscopic electrosurgical knives to resect the entire tumor364 (Fig. 54-9). In addition to an R0 resection, ESD allows for more precise histopathologic assessment of depth of invasion and lymphovascular involvement, and permits appropriate assessment for risk of lymph node metastasis. If preprocedure evaluation does not reveal regional lymph node involvement, much larger superficial lesions can be resected. The Japanese have developed expanded criteria for ESD for early gastric cancer: (1) mucosal intestinal-type cancer of any size without ulceration, (2) mucosal intestinal-type cancer less than 3 cm with ulceration, and (3) submucosal intestinal-type cancer less than 3 cm and with submucosal invasion less than 500 μm.365,366 As experience with this ESD has increased, en bloc resection rates are now reported to be over 90%, with local recurrence rates lower than 3%.364 Owing to the large size of some of the lesions being resected, the risk of gastric perforation is relatively high (2% to 6%).367,368 However, perforations recognized early can generally be treated conservatively with closure using endoscopic clipping.364 Limited data from Western centers with fewer patients report good but slightly lower resection rates and higher complication rates.369,370 For patients with EGC but higher risk of lymph node involvement and who are poor candidates for surgical gastrectomy, combination ESD with laparoscopic lymph node dissection may be an alternative approach.371 There are no published randomized clinical trials comparing surgery to endoscopic resection for early gastric cancer.