Activation of the mitogen activated protein kinase (MAPK) pathway is found in around 60% of pMMR colon cancers due to a constitutive activation of the small GTPase K-Ras (Kirsten rat sarcoma viral oncogene homolog) or other N-RAS (neuroblastoma rat sarcoma viral oncogene homolog). The gene discussed is KRAS; the disease is malignant colon neoplasm.