Study Evaluating the Efficacy of the myDIET Software Tool in the Nutritional Management of Patients With Localized and Resectable Gastric or Esogastric Junction Cancer.

Inclusion Criteria:

* Patient 18 years of age or older at date of signing informed consent to participate;
* Histologically proven diagnosis of gastric adenocarcinoma or OGJ;
* Localized, resectable disease;
* Patients with an indication for perioperative chemotherapy and/or immunotherapy validated in multidisciplinary consultation meeting, with a scheduled surgery date at least 1 month after enrolment;
* Performance status (ECOG): 0-2;
* Membership of a social security scheme;
* Signed informed consent to participate.

Exclusion Criteria:

* Other associated solid cancer or haemopathy;
* Presence of severe comorbidity (Charlson index \> 9)
* Presence of unbalanced dysthyroidism;
* History of gastric, duodenal or esophageal surgery;
* Inability to comply with study requirements, including :

  * Impossibility for the patient or his/her caregiver to connect to myDIET;
  * Difficulty in understanding the written French language;
  * Psychological incapacity (e.g. excessive vulnerability, psychiatric disorder) or physical incapacity (e.g. physical/motor disability);
* Patient under guardianship, curatorship or safeguard of justice;
* Patients already participating in a clinical trial or interventional study likely to interfere with the evaluation of the primary endpoint.
* Pregnant or breast-feeding patient.