ERBB2 and cancer: EFTUD2, being approximately 5 Mb telomeric to HER2, is sufficiently close to HER2 in non-amplified cancers to have robustly the same copy number as HER2. Therefore, the specificity is not compromised by chromosomal instability, which potentially complicates assessment based on reference probes on chromosomes other than 17, or on more distal probes such as peri-centromeric probes.