Polymorphisms in OATP1B1 (SLCO1B1), such as the OATP1B1*15 haplotype [11,14], both alone and accompanied by variants in other carriers, influence the response to methotrexate [15,16] and irinotecan in vitro [16,17], due to reduced transport activity; for the latter, this is the case in metastatic CRC patients, where it is used as a palliative treatment. Here, SLCO1B1 is linked to colorectal carcinoma.