ERBB2 and breast cancer: Were this method to be diffused amongst laboratories, a universal calibration reference should be used (e.g., cDNA from a known and well-studied breast cancer HER2-amplified cell line mixed at serial dilutions with donors’ cDNA, with the caveat of using the same batch of cancer cell lines from a commercial vendor due to the risk of copy number drift over time for cell cultures kept in individual laboratories).