GastrOesophageal Tumor, Immune Microenvionnment (GOTIM)

Inclusion Criteria:

• Male or female patient > 18 years of age on day of signing informed consent.
• Histologically proven non-metastatic resectable gastric and gastroesophageal junctionadenocarcinoma, Stage IB to III to be treated with standard neoadjuvant treatment.
• Surgery of primary tumor to be done at Centre Léon Bérard.
• Availability of archival FFPE tumor block from initial diagnosis with at least 20% oftumor cells.
• Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0, 1 or 2.
• Patient should understand, sign, and date the written voluntary informed consent format the screening visit prior to any protocol-specific procedures performed. Patientshould be able and willing to comply with study visits and procedures as per protocol.
• Patients must be covered by a medical insurance.

Exclusion Criteria:

• Any condition contraindicated with blood sampling procedures required by the protocol.
• Known additional malignancy that is progressing or requires active treatment.Exceptions include adequately treated basal cell carcinoma of the skin, squamous cellcarcinoma of the skin, or in situ cervical cancer
• Any psychological, familial, geographic or social situation, according to the judgmentof investigator, potentially preventing the provision of informed consent orcompliance to study procedure.
• Pregnant or breast-feeding woman.