A case of lymph node metastasis following a curative endoscopic submucosal dissection of an early gastric cancer
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Currently in Japan, differentiated gastric submucosal invasive cancers <500 μm (SM1) with negative lymphovascular involvement are included in expanded pathological criteria for curative endoscopic treatment. This is based on a retrospective examination of surgical resection cases in which patients suitable for such expanded criteria were determined to have a negligible risk of lymph node metastasis. We performed endoscopic submucosal dissection on a 65-year-old male with early gastric cancer in April 2005, and pathology revealed a well-differentiated adenocarcinoma, 21 × 10 mm in size, SM1 invasion depth and negative lymphovascular invasion as well as tumor-free margins, so the case was diagnosed as a curative resection. This case, however, resulted in lymph node metastasis that was diagnosed by endoscopic ultrasonography with fine-needle aspiration biopsy in May 2009. Distal gastrectomy with D2 lymph node dissection was then performed, confirming lymph node metastasis from the original gastric cancer.
KeywordsEarly gastric cancer Lymph node metastasis Expanded criteria ESD SM1
Endoscopic resection is the preferred treatment method for the local dissection of early cancer with a negligible risk of lymph node metastasis. For early gastric cancer (EGC), it is possible to achieve nearly 100% curability by radical surgery; therefore, it is an absolute requirement to maintain such a level of curability with endoscopic resection. In Japan, the Gastric Cancer Treatment Guideline (3rd version) specifies that the pathological criteria for curative endoscopic resection are limited to small intramucosal differentiated-type gastric cancer ≤20 mm in size without an ulcer finding . Recently, the pathological criteria for curative endoscopic resection of EGC have been expanded to cover other lesions with a negligible risk of lymph node metastasis . These expanded criteria include larger lesions, lesions with ulceration and lesions that invade the submucosa <500 μm (SM1).
Together with advances in treatment equipment used for endoscopic resection in recent years, endoscopic submucosal dissection (ESD) provides a higher en bloc resection rate, thus allowing for more accurate and detailed pathological evaluation compared to endoscopic mucosal resection (EMR) [3, 4, 5, 6, 7, 8]. Due to the refinement of ESD and the acceptance of the expanded pathological criteria for curative endoscopic resection, which in turn resulted in expanded clinical indications for endoscopic resection, the number of patients who are treated by endoscopic resection has increased dramatically.
We experienced for the first time a case of lymph node metastasis following ESD resulting in a pathologically curative resection of SM1 EGC and report this case here.
We previously reported a group of patients with negligible risk of lymph node metastasis based on the pathological examination of over 5,000 surgical EGC cases that developed into the current expanded pathological criteria for curative endoscopic resection of EGC . The expanded criteria include differentiated adenocarcinomas with negative lymphovascular involvement that are either intramucosal cancer without ulcer findings regardless of tumor size, intramucosal cancer with ulcer finding ≤3 cm in size or SM1 cancer ≤3 cm in size. Patients who were treated following these expanded criteria have had similar long-term outcomes to those treated according to traditional guideline criteria (5-year survival rate of expanded criteria vs. traditional guideline criteria: 93.4 vs. 92.4%) . In recent years, Nagano et al.  reported two cases of lymph node metastasis of SM1 cancer; however, one patient was previously treated by endoscopic piecemeal resection, and submucosal lymphatic involvement was observed in the other case. No lymphovascular involvement was observed in the present case, however, and this is the first case of a curative resection based on the SM1 expanded criteria in which lymph node metastasis was observed during careful follow-up.
We speculate that there are two possible explanations for such lymph node metastasis. First, we have previously reported that SM1 gastric cancer differentiated adenocarcinomas with negative lymphovascular involvement ≤3 cm in size had a 0% rate (0/145) of lymph node metastasis with a 95% confidence interval (CI) upper limit of 2.5% . The risk of lymph node metastasis for such SM1 gastric cancer is slightly higher, however, than for the expanded criteria for intramucosal cancer. Second, the resected specimen revealed a predominantly well-differentiated adenocarcinoma, but a poorly differentiated adenocarcinoma component also was identified in the proximal portion of the lesion, although it was not in the area of SM1 infiltration and separate from the ulcer scar. A similar case of lymph node metastasis following ESD has been reported involving such a mixed type adenocarcinoma, and the patient subsequently died of liver metastasis 33 months after ESD .
In our case, lymph node metastasis was pathologically confirmed by EUS-FNA, and radical surgical treatment was performed, thus far resulting in the patient having no recurrence. Needless to say, careful follow-up is necessary after endoscopic resection, but it is difficult for current diagnostic imaging equipment to differentiate whether slightly enlarged lymph nodes, as in the present case, are non-malignant or metastatic . Iwashita et al.  analyzed the enlarged lymph nodes of 62 patients and reported EUS-FNA sensitivity to be 97% with a specificity of 100%. EUS-FNA was also effective in the present case; therefore, we believe that EUS-FNA can be of assistance in making an accurate diagnosis for patients with enlarged lymph nodes.
We have to maintain careful follow-up, keeping in mind that metastasis may possibly occur even in a case of curative resection based on the expanded pathological criteria.
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