ERBB2 and breast cancer: Known HER2-positive BC defined as an IHC status of 3+. If IHC is 2+, a positive in situ hybridisation (FISH, CISH or SISH) test is required by local laboratory testing. ISH positivity is defined as a ratio of ≥2 for the number of HER2 gene copies to the number of signals for chromosome 17 copies.