ERBB2 and cancer: For example, a pre-clinical study found that trastuzumab can decrease cancer cell proliferation in HER2 negative and HER2 phosphorylation at tyrosine Y877 positive breast cancer cell lines, which is comparable to the drug effect in HER2 positive breast cancer cell lines, showing that the HER2 negative subpopulation may also benefit from trastuzumab [6].