When reviewed by a pathologist (KS), IHC of BT474 tumor specimens scored as HER2-positive (3+), while both MDA-MB-453 and BT20 specimens both scored as clinically equivocal (2+) for HER2; we speculate the difficulty in distinguishing HER2 expression in the latter two specimens compared to western blotting relates to the known variability of IHC results that may occur based on factors such as reagents used, epitope accessibility, and staining technique48–50. Here, ERBB2 is linked to neoplasm.