To conduct a retrospective study to prove a hypothesis of "adjuvant chemotherapy provides survival benefit for patients of CTX-benefit group in gastric cancer of pT1N1, especially in high-risk group". This study is a pilot study and the result will be used as a reference for the upcoming prospective randomized controlled trial for same issue including estimating sample size. Two high-volume hospitals (Yonsei University Severance Hospital and Samsung Hospital) will participant this pilot study.

FFPE sample blocks and clinical information pertaining to the patients who satisfied with selection criteria will be collected from two institutions. The primary end point of this study is disease-free survival (DFS) that is defined as the time from surgery to death or gastric cancer recurrence whichever occurred first; and overall survival (OS) that is defined as time from surgery to death by any causes. Clinical information such as age, sex, histology, Lauren classification, depth of invasion, number of retrieved and metastatic lymph nodes, sizes of tumor, location of tumor, gross type, lympho-vascular invasion, received chemotherapy or not will be centralized.

One or 2 of 3mm core of tumor will be punched from FFPE and it will be delivered through Eppendorf tube to laboratory (Novomics Co. Ltd., Seoul, Korea). RNA will be extracted from the tissue and the pattern of RNA expression will be evaluated and each sample will be categorized into three risk group (high, intermediate, low risk group) and two predictive group (CTX-benefit and no-benefit group) by GMP-grade nProfiler 1TM Stomach Cancer Assay Kit (Novomics Co. Ltd., Seoul, Korea). Both clinical information and classification will be delivered to independent statisticians who are responsible to conduct statistical analyses.

Inclusion Criteria:

1. Pathologically confirmed gastric adenocarcinoma
2. Patients who received R0 resection with curative intent surgery
3. pT1 (mucosa/submucosa) N1(one or two metastatic lymph nodes) M0
4. patients received surgery with lymph node dissection of D1 + or more
5. number of retrieved lymph nodes >15
6. Formalin-Fixed Paraffin-Embedded cancer tissues are available
7. Adults over 19 years

Exclusion Criteria:

1. Patients received pre-operative chemotherapy or radiotherapy
2. Cancer in remnant stomach (history of gastrectomy)
3. in hospital mortality or died within 30 days after surgery
4. FFPE is not available

approximately 1,000 patients Formalin-fixed, paraffin-embedded (FFPE) sample blocks from patients who treated at Severance Hospital and Samsung Hospital for gastric cancer (satisfied with below criteria) with pT1N1 stage and their corresponding clinical information will be evaluated from 1990-2012, approximately 500 participants in each hospital).