PGP and neoplasm: Abnormal expression of drug-resistance proteins such as permeability glycoprotein (P-gp), annexin A1 (ANXA1), and ATP-binding cassette superfamily G member 2 (ABCG2) have been found in colorectal tumour tissues of patients with primary MDR, resulting in different levels of drug resistance to chemotherapy drugs in tumour cells [5–7].