Pharmacokinetics of Oral Antiplatelet Agents After Distal Gastrectomy

Inclusion Criteria: * Patients diagnosed with pathologically proven gastric cancer of clinical stage I according to the AJCC 8th edition. * Patients who are scheduled to undergo distal gastrectomy (access: either minimally invasive surgery or open surgery) * Patients taking aspirin and/or clopidogrel for primary or secondary prevention for cardiovascular disease or cerebrovascular disease before surgery. * age 18 - 90 years * A person who voluntarily agrees to participate in this study and signs the consent form. Exclusion Criteria: * Patients with coagulation disorder or abnormal findings in coagulation test (low platelet count, prolonged PT/aPTT) * Patients taking other anticoagulants in combination * Patients with imparied liver or renal function that may affect drug metabolism. Impaired liver function: liver cirrhosis Impaired renal function: CKD grade 3 or higher * Patients requiring adjuvant chemotherapy after surgery that may affect postoperative bone marrow function and hematopoietic function (those with gastric cancer of clinical stage II or more according to the AJCC 8th edition) * Patients participating in other clinical trials within 6 months * Vulnerable patients (pregnant women, those with cognitive impairment, etc)