Kaplan-Meier estimates of FFS probability, stratified by EBV status. (A) FFS by EBER-ISH status. EBER-ISH(-) (n = 264, solid line) and EBER-ISH(+) (n = 51, dashed line) (B) FFS by plasma EBV-DNA status. Pretreatment plasma EBV(-) (n = 220, solid line) and pretreatment plasma EBV(+) (n = 54, dashed line). P values for log-rank comparison of curves are given in the bottom left hand corner of each figure. HR, hazard ratio.