ERBB2 and breast cancer: To date, the selection of BC types likely to respond to trastuzumab, is based on the detection of sufficient Her-2 protein on the cell surface by immunohistochemistry (IHC) and in situ hybridization techniques as FISH, SISH or CISH which identifies the number of HER2 gene copies on chromosome 17 also in relation to centromere 17 (CEP17) copies per nucleus.