TY - JOUR T1 - <em>MLL</em> rearranged acute lymphoblastic leukaemia presenting as a maxillary sinus mass with a discordant immunophenotypic profile from the bone marrow JF - BMJ Case Reports JO - BMJ Case Reports DO - 10.1136/bcr-2018-227400 VL - 12 IS - 2 SP - e227400 AU - Yunzu Michele Wang AU - Jun Qin Mo AU - Dennis John Kuo AU - Victor Wong Y1 - 2019/02/01 UR - http://casereports.bmj.com/content/12/2/e227400.abstract N2 - We describe an unusual case of pre-B lymphoblastic leukaemia presenting with a unilateral maxillary sinus mass in which biopsies of the primary mass and the bone marrow demonstrated conflicting immunophenotyping results. The extramedullary mass was consistent with a precursor B-cell malignancy, while the bone marrow was initially reported as a possible mature B-cell malignancy. The treatments for the two are fundamentally different, which necessitated a delay in the initiation of his chemotherapy until a clear diagnosis was made. Mixed lineage leukaemia gene rearrangement was confirmed by fluorescence in situ hybridisation in both the primary mass and bone marrow, which unified the diagnosis as pre-B acute lymphoblastic leukaemia given the common cytogenetic feature. ER -