ABCB1 and colorectal carcinoma: On the other hand, the overexpression of ABCB1 in tumors leads to the progression of MDR in cancer cells against many common drugs that serve as ABCB1 substrates, such as doxorubicin, paclitaxel and vincristine [27,28,29], particularly in CRC [30,31,32,33,34,35].