BCL2 and cancer: Several mechanisms are currently related to 5-FU chemoresistance and treatment failure in CRC, such as Bcl-2 and Bcl-xL overexpression in cancer cells, p53 gene mutations, 5-FU efflux induced by the increased expression of the ATP-binding cassette transporter, nucleoside metabolizing enzymes overexpression, along with mismatch repair system disruption [80].