RPA1 and nasopharyngeal carcinoma: The proposed RPA stage system divided nonmetastatic NPC into RPA-I (low risk: T1-3N0 or EBV DNA–negative T1-3N1), RPA-II (moderate risk: EBV DNA–positive T1-3N1-2 or EBV DNA–negative T1-3N2-3/T4N0-3), and RPA-III (high risk: EBV DNA–positive T4N0-3/T1-3N3).