PCR-based analyses in combination with other approaches (cytogenetics, FISH, and immunophenotyping) have allowed us to define various distinct ALL subtypes, part of which already defines separate entities within the WHO classification of 2008, for example, the t(9;22)/BCR-ABL1 or the t(12;21)(p13;q22)/ETV6-RUNX1. Here, ABL1 is linked to acute lymphoblastic leukemia.