Olanzapine in the Prevention and Treatment of Anorexia-Cachexia Syndrome in Patients Receiving Neoadjuvant/Preoperative Chemotherapy

The goal of this clinical trial is to learn if olanzapine works to prevent and treat anorexia-cachexia syndrome and appetite loss in cancer patients. The main questions it aims to answer are: Is prolonged low-dose olanzapine effective and save in: * Preventing/treating weight loss due to anorexia. * Controlling nausea/vomiting. * Maintaining anticancer therapy dose intensity? Does prolonged low-dose olanzapine improve quality of life in patients receiving neoadjuvant/preoperative chemotherapy? Participants will: Take prolonged low-dose olanzapine (2.5 mg/day) in treatment group or usual diet only in control group until surgical treatment Physical examination, anthropometric assessment, blood tests, quality of life, appetite and nutritional status assessment, abdominal CT, handgrip dynamometry before chemotherapy and after preoperative chemotherapy before surgery Physical examination, adverse events every visit Surgical complications within 30 days after surgery