UNUSUAL CASE OF THERAPY RELATED B-ALL WITH MLL GENE REARRANGEMENT

Case presentation A 56-year-old female had a FBC that showed 90% blasts in the peripheral blood film. The blasts resembled lymphoblasts by morphology. Flow cytometry confirmed a B-ALL associated immunophenotype: CD34–, TdT–, HLA-DR+, CD19+, cCD79a+, CD10–, CD20–, with aberrant expression of the myeloid antigen CD15 (moderate). Other T lymphoid, myeloid and NK-cell antigens were all negative including cCD3, MPO and CD117. The aberrant expression of CD15 prompted us to investigate for MLL gene rearrangement. FISH analysis using the Vysis MLL Dual Colour Breakapart rearrangement probe showed evidence of rearrangement of the MLL locus at 11q23 in 91% of interphase nuclei. t(9;22)(q34;q11.2) was not detected. This occurred while the patient was being treated for breast cancer with a combination of cyclophosphamide (alkylating agent), doxorubicin (topoisomerase II inhibitor), paclitaxel and trastuzumab. Discussion Therapy-related acute leukaemia is a known complication of systemic chemotherapy. They are mostly myeloid; the prevalence of therapy-related ALL is only 1.2–2.5% of all adult ALL. Topoisomerase II inhibitors are associated with a short latency period between treatment and development of leukaemia and are not preceded by myelodysplasia. Commonly, they are associated with cytogenetic abnormalities involving the chromosome 11q23 (MLL gene locus). The prognosis is poor in general and patients should be considered for allogeneic stem cell transplant.