Moreover, biological factors significantly impact 5-FU response, including patient age, gender, tumor site, histological grade, disease stage, Kirsten rat sarcoma virus (KRAS) mutation status, microsatellite instability (MSI), telomere length, and tumor-infiltrating lymphocytes (TILs) [4,16,17,18,19,20,21,22]. The gene discussed is KRAS; the disease is neoplasm.