Truncated HER2 proteins, which are predominantly found in breast cancers, derive from lack of substantial parts of the extracellular domain, either from proteolytic shedding of the ectodomain of the full-length receptor (p95HER2) or alternative mRNA translation from internal initiation codons (HER2 carboxyl terminal fragments) [reviewed in Ref. Here, ERBB2 is linked to breast carcinoma.