Further experiments indicated that the 5’ end of the ABCB1 mRNA in normal colon cancer cells was shorter than in doxorubicin resistant breast cancer cells, and alternative promoters were responsible for the PGP post-transcriptional regulation, which exhibited increased ABCB1 mRNA expression but unchanged protein expression and PGP efflux function [40]. This evidence concerns the gene ABCB1 and breast cancer.