Additional Chromosomal Abnormalities in Philadelphia Chromosome-Negative Metaphases Appearing during Therapy with Imatinib, Dasatinib, Nilotinib and Ponatinib in Patients with Newly Diagnosed Chronic Myeloid Leukemia

Background

Additional chromosomal abnormalities (ACAs) in the Philadelphia chromosome (Ph)-negative metaphases that emerge as patients with chronic myeloid leukemia (CML) are treated with tyrosine kinase inhibitors (TKIs) have been reported during treatment with imatinib. It has been suggested that these might be associated with an inferior outcome and in rare instances lead to the emergence of a new malignant clone resulting in myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) (Jabbour et. al, Blood 2007). This phenomenon has not been well characterized when other TKIs are used. We conducted a retrospective analysis of patients treated on imatinib, dasatinib, nilotinib, and ponatinib frontline trials to assess the frequency and prognostic impact of ACAs appearing during the treatment after achieving cytogenetic response.

Patients and Methods

A total of 524 patients with CML were evaluated with a median age at diagnosis of 48 years (range 15 to 86). These included 236 patients treated with imatinib, 125 with nilotinib, 118 with dasatinib and 45 with ponatinib. All the patients were treated in clinical trials approved by the institutional board review and signed an informed consent in accordance with institutional guidelines and in accordance with the declaration of Helsenki. Conventional cytogenetic analysis was done in bone marrow cells using standard G-banding technique at baseline, every 3 months during the first year, then every 6-12 months. Clonal ACAs were identified as abnormalities present in ≥2/20 metaphases or, if only one metaphase, present in ≥2 consecutive assessments. 

Results

After a median follow-up of 83.8 months (range 0.3-176.6 months) 13% (72/524) patients had ACAs, of which 7% (41/524) were clonal. ACAs were seen in 11% (27/236) of patients on imatinib compared to 11% (13/118, p=0.9) on dasatinib, 19 % (24/125, p= 0.04) on nilotinib, and 17% (8/45, p=0.2) on ponatinib. Six patients had both clonal evolution (CE) and ACAs at different times. The median number of metaphases containing ACAs was 5/20 (range 1 to 20) with an average of 7/20. Most appeared within the first year of the start of the TKI (median 6 months, range 3-72 months); they first appeared after 12 months of therapy in 21 of the 72 (29%) patients. ACAs were transient and were detected in 2 or less time points in 52 of the 72 (72%) cases. The most common clonal ACAs were – Y (13/41) and +8 (4/41). The rates of cytogenetic and molecular responses were similar for patients with and without clonal ACAs (CCyR: 88% vs 91%; p=0.55) (MMR: 78% vs 86%, p=0.20). Having clonal ACAs did not affect the rate of deep molecular response either (MR^4.571% vs 67%; p =0.65). There was no significant difference in EFS and OS (5y EFS 73% vs 86%; p=0.19) (5y OS 77% vs 93%; p=0.06) although there was a trend for lower rates for both. Responses and clinical outcomes were similar between different TKIs for patients with and without clonal ACAs. One patient with -7 treated with ponatinib developed MDS. Monosomy 7 appeared 9 months from the start of treatment in 9/20 metaphases and persisted. He was taken off ponatinib because of pancytopenia. He subsequently received bosutinib, achieved and maintained a CCyR. A high-risk MDS was documented approximately 1 year after appearance of the -7 clone. He was started on decitabine and achieved a partial cytogenetic response for MDS. Another patient in the imatinib cohort with -7 developed secondary AML (CCyR for CML) and died from a multiple organ failure after allogeneic stem cell transplant from a one antigen-mismatched unrelated donor. There was a third patient with -7 that later had CE and developed Ph+ CML blast phase.

Conclusion

ACAs are rare and mostly transient events that appear during the treatment of CML with TKIs. These changes do not affect responses or clinical outcomes, independent of what TKI is used. A small subset of patients with -7 may develop AML or MDS warranting close monitoring of patients with changes that are reminiscent of those diseases. Molecular analysis after appearance of ACAs could help identify mutations driving the Ph-clone into AML or MDS.