Introduction:
The MLL gene (Mixed Lineage Leukaemia gene) is a positive regulator of the HOX gene which is required for normal haemopoiesis.  Alterations in this gene favour leukemic maturation in either the myeloid or lymphoid lineage. MLL rearranged acute lymphoblastic leukaemia is usually a disease of infants <12 months of age and is a relatively rare haematological malignancy in adults. It may also present as a therapy related acute leukaemia, usually with myeloid lineage.

Clinical presentation:
Patient MO was a 40 year old female who presented with neurological symptoms arising from leukostasis.  Leucophoresis was performed over 4 days to reduce her white cell count (WCC) to normal levels and to minimise the risk of tumour lysis syndrome with the commencement of induction chemotherapy. Despite several courses of aggressive chemotherapy, she has only achieved a brief 3 month remission. 

Results:
The full blood count on presentation showed a WCC of 359.4 x 10⁹ /L, of which 251.6 x  10⁹/L were blasts with morphological features of L2 blasts of the FAB classification. D-Dimer was moderately raised at 13.3 ug/ml FEU.  Flow cytometry results were consistent with an early -B lymphoid phenotype (CD19 +ve, CD79 weak +ve, CD34+ve, HLA DR +ve, TDT +ve, CD10-ve), and variable CD15+ve was suggestive of rearranged MLL.   Dual –colour breakapart FISH probes demonstrated   the MLL fusion in 84% of interphase cells examined. The karyotype at diagnosis was 46XX, t(4;11) (q21;q23) karyotype and an  additional isochromosome 7 at 5 months post diagnosis. 

Conclusion:
This case of adult B -ALL with 11q23 rearrangement highlights its notorious disease course and poor prognosis, featuring resistance to chemotherapy and difficulty in achieving complete remission