In total, 769 bone marrow and/or peripheral blood samples from 193 adult ALL patients with KMT2A rearrangement (175 KMT2A::AFF1, 13 KMT2A::MLLT1, 1 KMT2A::MLLT3, 4 KMT2A+ unspecified) obtained between 2001 and 2021 were available for longitudinal MRD measurements. The gene discussed is MLLT1; the disease is acute lymphoblastic leukemia.