Our studies have demonstrated that MTDH expression in 4 types of breast cancer cells was different, and revealed an ascending order as MDA-MB-231 (ER-, PR-, HER-2-), MCF-7 (ER+, PR+, HER-2-), MDA-MB-435S (ER-, PR-,) and MCF-7/ADR. This evidence concerns the gene ERBB2 and breast cancer.