Inclusion Criteria:

- Patients be able to grant a written informed consent or oral consent

- Age ≥18 years old

- Patients diagnosed with metastatic gastric or gastro-esophageal junction
adenocarcinoma (HER2-positive), unresectable and histologically confirmed Measurable
disease, following the new RECIST criteria,

- HER2 positive tumors (primary or metastatic) with overexpression HER2 determinated by
IHQ +++ (IHQ3+) o IHQ ++ confirmed by FISH/SISH positive (IHQ2+/FISH+)

- ECOG ≤ 2

- Patients of childbearing potential (< 12 months from last menstruation), they have
to use effective means of contraception

- Life expectancy more than 3 months

- Adequate renal function: calculated creatinine clearance > 50 mL/min

- Adequate liver function: AST and ALT ≤2.5 x LSN (5 x LSN with liver metastasis),
bilirubin 1,5 x LSN. alkaline phosphatase < 2,5 x LSN (≤ 5 x LSN with liver
metastasis o < 10 x LSN with bone metastases Adequate haematological function: Hb ≥9
g/dl, neutrophils ≥ 1,5 x 109 /l and platelets 100 x 109 /l.

- Normal Left Ventricle Fraction Ejection , LVEF> 50%

- Every patient should be treated and followed in his / her study site

Exclusion Criteria:

- Prior chemotherapy treatment for advanced/metastatic disease

- Lack of physical integrity of the upper gastrointestinal tract or malabsorption

- Patients with active gastrointestinal bleeding

- Prior chemotherapeutic treatment for advanced / metastatic disease

- Toxicity as a result of prior therapy (except alopecia)., for example.

- Neurology toxicity grade ≥2NCI-CTCAE

- Patients who received radiotherapy within 4 weeks prior to study treatment.

- Major surgical procedures within 4 weeks prior to treatment without a total surgical
recovery.

- Past or current history of other malignancies (within the last 5-2 years prior to
treatment start), patients with curatively treated basal cell carcinoma of the skin
or in situ carcinoma of the cervix are eligible

- Active and clinically significant cardiovascular disease,

- History or current clinical evidence of brain metastasis

- Patients undergoing transplantation allogenic requiring immunosuppressive treatment

- Moderate or severe renal failure, creatinine clearance < 50 mL/min, calculated by
Cockcroft-Gault

- Adequate liver function: bilirubin ≤1.5 x UL, GOT ( ASAT )/ GPT ( ALAT ) ≤2,5 LSN.
Liver metastasis ≤ 5 x LSN, FA ≤ de 2,5 feces el LSN.

- Adequate haematology function: neutrophils ≥ 1,5 x 109 /l and platelets 100 x 109
/l

- Treatment with sorivudine and the analogous as brivudine.

- Dihydropyrimidine proven dehydrogenase deficiency (DPD).

- Patients who had received any drug, agent or investigational procedure, or who have
participated in another research study within 30 days prior to initiation of
treatment with study medication.

- Hypersensitivity to any of the study drugs

- Evidence of any other disease, metabolic dysfunction, physical examination finding or
laboratory finding giving reasonable suspicion of a disease or condition that
contraindicates the use of an investigational drug or puts the patient at high risk
for treatment-related complications

- Patients receiving chronic corticosteroid therapy or high dose (is allowed to use
inhaled steroids and cycle short treatment with oral steroids for prevention of
emesis or to stimulate appetite)

- Pregnancy and lactation

- Patients of childbearing potential not willing to use effective means of
contraception.

- History of psychiatric disorders that the investigator considered clinically
significant, causing the patient give informed consent or interfere with compliance
with study procedures.