In HER2-positive breast cancer, there is overexpression of the HER2 gene and other genes in the HER2 signaling pathway, increased expression of genes involved in cell proliferation and survival, such as MYC and BCL2, high expression of genes involved in DNA repair and genomic stability, such as BRCA1 and BRCA2, and low expression of genes involved in immune response and inflammation, such as TNF and IL6. This evidence concerns the gene BRCA1 and breast cancer.