- Patients must have HER2-positive (FISH+ or IHC 3+) metastatic or unresectable gastric or gastroesophageal junction (GEJ) adenocarcinoma to be eligible for trastuzumab. For the purposes of this protocol, FISH+ is defined as HER2:CEP17 ratio ≥ 2.0. Biopsy samples with cohesive IHC3+ or FISH+ clones are considered HER2 positive irrespective of size, i.e.<10%. FISH+ defined as >2 HER2:CEP17.