The variant allele of the non-synonymous BCRP C421A (Q141K) polymorphism has been associated with lower protein levels and lowered transport activity both in vitro [34,35] and in vivo [27,35], but no associations were found between either the intestinal levels of protein and mRNA and BRCP polymorphisms [36] or between BCRP polymorphisms and risk of CRC [4]. Here, ABCG2 is linked to colorectal carcinoma.