ERBB2 and breast cancer: When the gastric PDX (EK) was passaged sc in DKO mice, and treated with iv PBMC (1 × 107, once a week × 3 weeks), and iv HER2-BsAb (100 ug, 2 ×/wk × 5 weeks), tumors were completely eradicated without disease progression (Fig. 6A), accompanied by substantial amount of T cell tumor infiltration (Fig. 6B), even though the HER2 expression level was relatively low compared with the M37 breast cancer PDX described next (Fig. 6C).