- For gastric cancer (including GE junction tumors): documented 3+ by immunohistochemistry, or 2+ by immunohistochemistry and amplification by in situ hybridization OR, ii) (Dose escalation part only): Recurrent or metastatic SCCHN regardless of HER2 status for which no effective treatment option exists OR, iii) Recurrent or metastatic ESCC regardless of HER2 status for which no effective treatment option exists