In our studies of trastuzumab responses in a panel of breast cancer cells, MDA-MB-453 (IHC HER2 2 + /FISH-) and MDA-MB-361 (IHC HER2 2 + /FISH + ) cells have shown only moderate responses to trastuzumab when compared to HER2 over-expressing (IHC 3 + ) BT474 and SKBR3 cells. Here, ERBB2 is linked to breast carcinoma.