Heterogenous expression of bcr‐abl fusion mRNA in a patient with Philadelphia‐chromosome‐positive acute lymphoblastic leukaemia

We performed molecular and cytogenetic analysis on a 56-year-old woman with Philadelphia chromosome (Ph1)-positive acute lymphoblastic leukaemia (ALL) having two types of major and minor bcr-abl (M-bcr-abl, m-bcr-abl) fusion mRNA at diagnosis. In the course of her disease, unexpected heterogenous bcr-abl fusion mRNA was detected by sequential analysis using the reverse transcription and polymerase chain reaction (RT-PCR). The RT-PCR analysis showed both M-bcr-abl (b2-a2 type) and m-bcr-abl at diagnosis. Although b2-a2 type M-bcr-abl disappeared after complete remission (CR) was achieved with intensive induction chemotherapy, expression of both m-bcr-abl and a new type of M-bcr-abl mRNA (b1-a2 type), which may have been produced through splicing out of exon b2, was detected in the early stage of CR. The leukaemic cells contained these heterogenous bcr-abl mRNAs in both the CR and relapsed state, and showed more stable expression of the m-bcr-abl type mRNA than that of the b2-a2 type. These findings of heterogenous bcr-abl mRNA due to alternative or missplicing during the disease course in the present ALL case may provide important evidence of disease progression.