Philadelphia-Positive Acute Myeloblastic Leukemia: A Rare Entity

The Philadelphia chromosome was first discovered in Philadelphia in 1960. It corresponds to shortened chromosome 22 resulting from reciprocal translocation between long arm of chromosome 9 and short arm of chromosome 22, which is designated as t(9;22)(q34;q11). This gives rise to a BCR/ABL fusion gene, that juxtaposes the ABL1 gene on chromosome 9 (region q34) to a part of the BCR ("Breakpoint Cluster Region") gene on chromosome 22 (region q11). There are two major forms of the BCR/ABL fusion gene of different sizes involving ABL exon 2 with different exons of BCR gene. Major BCR (M-BCR) resulting in b2a2 and b3a2 mRNA transcripts, p210 chimeric protein, are most commonly involved in CML patients. Minor BCR (m-BCR), e1a2 mRNA transcripts and p190 chimeric protein, are most frequently associated with Ph positive Acute lymphoblastic leukemia (ALL) and in many patients with CML. Third less common fusion gene involving breakpoint in micro BCR (μ-BCR), e19a2 and result in p230 chimeric protein, may demonstrate prominent neutrophilic leukocytosis; these should be diagnosed as chronic neutrophilic leukaemia [1,2].