In particular, they used the HER2 mean intensity signal of three BC cell lines with a known HER2 IHC expression (SKBR-3 – 3+, MDA-MB 453–2+, MDA-MB 231–0 or 1+) for defining HER2 expression thresholds: i) HER2 negativity (0 or 1+) with a mean intensity of zero; ii) intermediate HER2-expression (2+) for a mean intensity between 0 and 100; iii) high HER2 expression (3+), with a mean intensity above 100 [37]. This evidence concerns the gene ERBB2 and breast cancer.