We use the immunohistochemical expression of mismatch repair proteins (MutS protein homolog 2( MSH2),MutS protein homolog 6( MSH6) and PMS2（postmeiotic segregation increased 2 ）) to Determine the MSI status . When one antibodies or more show negative nuclear staining of the tumor cells, the MSI state can be defined as Microsatellite instability high (MSI-H).

We use the immunohistochemical expression of mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) to Determine the MSI status . when all the four antibodies show positive nuclear staining of the tumor cells, the MSI state can be defined as Microsatellite stable (MSI-L).

We use the immunohistochemical expression of mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) to Determine the MSI status . when all the four antibodies show positive nuclear staining of the tumor cells, the MSI state can be defined as Microsatellite stable (MSS).

The microsatellite instability status are definite to three type:MSI-H, MSI-L,and MSS. The gastric cancer patients who received D2 resection were included in 3 groups：MSI-H group， MSI-L group，and MSS group. All patient must be accept fluorouracil(5-FU) based adjuvant chemotherapy. We will analyze the relationship between MSI status and efficacy of 5-FU based adjuvant chemotherapy by observing the survival period of patients with different MSI status.

The time from the primary operation to disease recurrence or death.

The The time from operation to death or the last follow-up. The time from operation to death or the last follow-up.