ERBB2 and breast cancer: Early experiments using karyotyping and metaphase FISH in ERBB2-amplified HER2+ breast cancers showed that the classical pattern was high copy gain with the extra ERBB2 copies residing on one or more chromosomes, typically not the chromosome of origin (chromosome 17) but another chromosome, in “homogeneously staining regions” that contained co-amplified sequences from several other chromosomes [39].