When the analysis was restricted to 52 high-risk patients with an initial WBC count 10.0 10 ( 9 ) / L , the intergroup difference was statistically significant , with 4-year RFS rates of 58 % for the ATRA arm and 87 % for the tamibarotene arm ( HR , 0.26 ; 95 % CI , 0.07 to 0.95 ) .