MRC1 and colorectal carcinoma: Utilizing CRC cells with hMLH1 deficiency, which are representative of the majority of MSI-positive sporadic CRCs, our data confirmed some previous experimental reports that DNA MMR-deficient CRC cells are resistant to 5-FU [10–13] and support some clinical evidence that patients with stage II CRC with tumors that lost DNA MMR function do not derive a benefit from 5-FU-based chemotherapy.