MDM2 and neoplasm: However, the elucidation of the ARF-MDM2-p53 pathway, with the Arf gene serving as a sensor of oncogenic stresses, raised the question as to which is more important for tumor suppression: DNA damage sensing (ATM/ATR-CHK1/CHK2-p53 pathway) or oncogenic stress responses (ARF-MDM2-p53 pathway).