Witton et al. have examined the expression of EGFR1, HER2, EGFR3 and EGFR4 using immunohistochemistry in 220 breast cancer patients and found overexpression of EGFR1 in 16.4%, HER2 in 22.8%, EGFR3 in 17.5%, and EGFR4 in 11.9% of breast cancer tissues. This evidence concerns the gene ERBB2 and breast cancer.