MLLT1 and leukemia: For Case 3 (triple fusion: ETV6/RUNX1 + BCR/ABL + MLL/ENL), FISH detected ETV6/RUNX1 split signals (16%), BCR/ABL fusion signals (14%), and MLL split signals (12%) in bone marrow cells; Sanger sequencing validated all three fusion breakpoints, and multi-parameter flow cytometry showed the co-expression of leukemia-associated immunophenotypes (CD19+CD10+CD34+) in the same cell population, confirming that these fusions originated from the same leukemia clone rather than cross-contamination of multiple clones.