In Part 1, groups of adult patients (pts) with HER2+ BC or HER2+ GC, who are resistant or intolerant to standard therapy or for which no standard therapy is available, received PF-06804103 intravenously once every 21 days (Q3W)...Preliminary ORR in the patients treated with doses ≥3mg/kg was 52.4% (11/21)....The PF-06804103 ADC demonstrated manageable toxicity and promising anti-tumor activity in this small, heavily pretreated study population.