PDTOs can be useful to clarify the conflicting literature on the predictive importance of primary tumor location on anti-EGFR antibody therapy in metastatic CRC patients with wild-type KRAS. Thus, some studies have found a greater effect of chemotherapy plus anti-EGFR as compared to chemotherapy alone or chemotherapy plus anti-VEGFR in patients with left-sided tumors, but not in patients with right-sided tumors [131,132,133]. This evidence concerns the gene KRAS and colorectal carcinoma.