In the trial AIEOP-BFM 2009, the HR stratum was defined by (1) KMT2A-AFF1, (2) low hypodiploidy, (3) PPR, (4) FCM-MRD d15 HR, (5) IF, (6) PCR-MRD HR, and (7) patients with BCP-ALL and MRD load of ≥10−3 at EOI and any PCR-MRD positivity below 10−3 at EOC (TP2, slow early responders, SER). Here, AFF1 is linked to acute lymphoblastic leukemia.