The mouse engrafted with the PALNTB PDX was euthanized at Day 58 due to an undefined non‐leukemia‐related illness, the MLL‐1 mouse was euthanized at Day 62 due to a mouse‐related thymoma, while the ALL‐3 mouse (the best responder of all PDXs) was euthanized at Day 379 due to a prolapsed bowel. Here, KMT2A is linked to thymoma.