A total of 198 newly diagnosed B-ALL patients, including 21 BAL patients, were admitted to CHCMU and CWCCH between January 2017 and November 2019, and 3 BAL patients with MLL transcripts were identified, accounting for 1.37% of the B-ALL population. The gene discussed is KMT2A; the disease is precursor B-cell acute lymphoblastic leukemia.