KRAS and colorectal cancer: let-7 could downregulate KRAS with anticancer effects in the presence of activating KRAS mutations, a higher let-7a levels were significantly associated with better survival outcomes in patients who were KRAS-mutated colorectal cancer and underwent third-line therapy with cetuximab (an anti-EGFR monoclonal antibody) plus irinotecan, suggesting that let-7 may restore anti-EGFR therapy effects in patients with chemotherapy-refractory metastatic disease [50].