Effects of ERBB2 amplicon size and genomic alterations of chromosomes 1, 3, and 10 on patient response to trastuzumab in metastatic breast cancer.

Trastuzumab is widely used for advanced breast cancer patients with ERBB2-amplified tumors. Nevertheless, over half of these patients do not have an objective response. One reason may be altered expression of genes that might compensate for ERBB2 inhibition.