Pre-Emptive Tyrosine Kinase-Inhibitor Intervention Based on BCR/ABL1 Monitoring in Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia after Allo-HSCT: Two Independent Observational Cohort Study - Hui, Liu; Xuan, Li; Lin, Ren; Deng, Lan; Huang, Fen; Fan, Zhiping; Nie, Danian; Li, Xudong; Liang, Xinquan; Xu, Dan; Zhang, Yu; Xu, Na; et al. (Blood, 2019)