ERBB2 and breast cancer: Moreover, both older and more recent studies show that ERBB2 RNA overexpression does not always correspond to erbB-2 protein overexpression, suggesting the existence of post-transcriptional regulation of ERBB2[61], [62], which shows the relevance of using RT-qPCR in routine assessment of ERBB2 overexpression in human breast cancer in the clinical laboratory setting.