Chronic Myeloid Leukemia (CML) Patients With Atypical e1a2 P190 BCR-ABL Translocation Show a Poor Response To Therapy With Tyrosine Kinase Inhibitors (TKI)

P210 BCR-ABL translocation resulting from rearrangements within the major breakpoint cluster region (M-BCR), either e13a2 or e14a2, is the molecular hallmark of chronic myeloid leukemia (CML). However, some CML patients may harbor atypical BCR-ABL rearrangements such e1a2 P190 BCR-ABL which involves the minor breakpoint cluster region (m-BCR). Response to therapy with tyrosine kinase inhibitors (TKI) and outcome of such atypical patients is not well defined.

To evaluate response to TKI therapy of CML patients with the atypical e1a2 P190 BCR-ABL translocation.

Since 2009, 4 patients with CML in chronic phase and with atypical e1a2 P190 BCR-ABL rearrangement have been recruited in various institutions belonging to the Hematological Molecular Biology Group (GBMH) of the Spanish Society of Hematology (SEHH). Patient characteristics, treatments administered and response to therapy for the 4 patients is shown in Table 1. BCR-ABL transcripts were revealed at diagnosis by quantitative PCR followed by conventional agarose electrophoresis of PCR products. Molecular follow-up of BCR-ABL transcripts throughout treatment was performed by quantitative PCR following the guidelines of the European Leukemia Net.

One patient received treatment (HU and INF+araC) prior to TKI (Pat. 1; Table 1). All 4 patients received Imatinib as initial TKI treatment. Two of the patients treated with Imatinib (Pat. 1,2) obtained a complete molecular response (CMR) and the other 2 (Pat. 3,4) only achieved a complete hematological response (CHR) as best response (Table 1). All patients had to switch to a second generation TKI (3 Nilotinib and 1 Dasatinib) due to intolerance to Imatinib (n=1; Pat. 1) or resistance (n=3; Pat. 2-4). The patient who received Dasatinib as second line TKI (Pat. 3) only achieved a partial hematologic response (PHR) and was changed to Nilotinib as third line TKI, achieving CHR after which the patient entered in blast crisis and died 36 months after diagnosis (Table 1). Overall, only 1 (Pat. 1) out of the 4 patients included in the present study achieved a sustained molecular response with Imatinib. At last follow-up, among the 4 patients included in the study, all 4 had needed a change of TKI, 1 had died due to disease progression (Pat. 3) and only 2 of them retained a molecular response (Pat. 1,2).

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CML patients harboring atypical e1a2 P190 BCR-ABL transcripts show a poor response and short-lived responses to TKI therapy and therefore should be identified as high-risk patients at diagnosis. These patients must be closely monitored during therapy with TKI and should be treated upfront with a second generation TKI or even be considered for allogeneic SCT in the early phase of the disease.

Paper presented on behalf of the Hematological Molecular Biology Group (GBMH) of the Spanish Society of Hematology (SEHH). AJ-V and IB contributed equally to this work.

No relevant conflicts of interest to declare.