* single center, prospective study First, evaluate the lesion under the white light endoscopy (WLE) → IV fluorescein sodium 0.1mL/kg → evaluate the lesion under probe-based confocal laser microendoscopy → target biopsy under the pCLE → random biopsy under WLE

The purpose of this study is to conduct a study on genetic pathology, obtaining of cancer tissues is mandatory. Although the endoscopy with biopsy has been a gold standard for diagnosing gastric cancer, percentage of cancer cells in biopsy samples of patients after chemotherapy is usually 30% or less. Because cancer cells are often replaced with regenerative cells after chemotherapy, even though there are still remnant cancer cells in the stomach. Recently, confocal laser endomicroscopy has been introduced for real-time histopathologic diagnosis in various cancers. In previous pilot study in our institution, pCLE-targeted biopsy provided superior results in terms of the proportion of cancer cells in biopsy samples compared to WLE-targeted biopsy, especially for gastric cancers with undifferentiated histology. However, there was no previous study about precious biopsy method for patients after chemotherapy. Therefore, the investigators aim to evaluate that biopsy using probe-based confocal laser endomicroscopy for remnant gastric cancer after chemotherapy will increase the percentage of cancer cells and expression ratio of tumor marker in biopsy samples.

Inclusion Criteria:

A. Older than 20 years old and younger than 80 years old B. Patients who completed neoadjuvant chemotherapy with AGC C. Patients who underwent palliative chemotherapy with AGC

Exclusion Criteria:

A. Previous subtotal gastrectomy B. Previous EMR/ESD history C. Significant cardiopulmonary disease D. Active hepatitis or severe hepatic dysfunction E. Severe renal dysfunction F. Severe bone marrow dysfunction G. Severe neurologic or psychotic disorder H. Pregnancy or breast feeding