Are CML Lymphoid Blast Crisis and Ph Positive ALL Genomically Indistinguishable?

Abstract 4464

Philadelphia positive malignant disorders are a clinically divergent group of hemoblastoses with a unique identifying feature, the BCR/ABL1 fusion gene, usually resulting from the chromosome rearrangement t(9;22)(q34;q11) or its variants, that leads to constitutive expression of an aberrant tyrosine kinase. These include chronic myeloid leukaemia (CML) and de novo acute leukaemia of both myeloid Ph(+)AML and lymphoid origin Ph(+)ALL. The latter two disorders are clinically aggressive and therapy challenging even in the era of the powerful tyrosine kinase inhibitors. CML is a multistage progressive disease, which if untreated, inevitably ends as fatal acute leukaemia, either myeloid or lymphoid. The latter is often thought to be indistinguishable from Ph(+)ALL, the most common type of ALL in adults. We have identified DNA sequences the imbalances of which appear to be significantly associated with the disease stage and lineage origin in CML and Ph(+)ALL samples. We used array CGH at a resolution of ~2kb to explore hot spot regions obtained from 102 patient samples comprising 92 CML and controls together with 10 Ph(+)ALL and show how Significance Analysis of Microarrays (1) can be used to identify differences in the genome profile of de novo Ph(+)ALL and lymphoid blast transformation of CML. We show that lymphoid blast crisis CML differs significantly from Ph(+)ALL not only due to the presence of 9p deletions but also due to genomic gains in other chromosomes. Furthermore we identify a sub group of Ph(+)ALL with a distinctive genomic profile. Having identified genome regions of potential interest, ranked in order of significance, out of the 100's of thousands of array results, it is then a challenge to design further experiments to evaluate their contribution to the biology of the BCR/ABL positive disease.

1 Tusher V, Tibshirani R, Chu G: Significance analysis of microarrays applied to the ionizing radiation response. Proc Natl Acad Sci U S A 98:5116-5121 (2001).