PI3K/RAS-mutations are associated with an average younger age at diagnosis in patients with KMT2A::AFF1 thereby likely affecting disease latency.5 In agreement, KMT2A-fusions cause leukemia in mouse models, with cooperating RAS-mutations shortening time to leukemia onset.28,32–36 Given that our patients carried small populations with such mutations, either they happened recently in time, or occurred in the wrong context for clonal expansion, including the possibility that they reside in nonmalignant cells. This evidence concerns the gene AFF1 and leukemia.