Imatinib as Second-Line Therapy, Ameliorates or Maintains Molecular Responses Obtained with Ponatinib First-Line in Chronic Phase CML Patients

Background & aims

The third generation tyrosine kinase inhibitor (TKI) Ponatinib demonstrates extremely potent BCR-ABL inhibitory activity in CML patients in chronic or advanced phase, resistant to 1, 2 or 3 prior TKI (Cortes NEJM, 2013) and it seemed interesting to test this agent in the front-line setting of chronic phase patients. The EPIC trial was a phase III trial set up to compare the molecular outcomes of Imatinib 400 (IM400) versus Ponatinib 45 mg daily at one year. However, this trial has been abrogated at early stages by the FDA despite the impressive molecular efficacy of Ponatinib (Lipton, Lancet Oncol 2016) because of unexpected and unacceptable rates of arterial thrombotic events that occurred in another trial (PACE). A majority of patients in the Ponatinib arm were switched towards IM400, but their outcome is not known. The aim of this study was to analyse the general and molecular outcomes of such patients in our country.

Methods

This is an observational study following the rules and regulations of these studies in our country. Data were monitored and retrospectively collected in the 5 centers involved in the EPIC trial. Molecular analyses were performed locally during ponatinib exposure (in parallel with centralised assessments) and during IM treatment thereafter. Only local results, expressed in % BCR-ABL (IS), were used in this analysis, and all respective molecular biology laboratories have been involved in the Eutos/ELN BCR-ABL accreditation system.

Results

Thirteen patients were analysed, 9 males and 4 females, with a median age of 58.5 (range 19.5-69) years at chronic phase CML diagnosis. Sokal scores were low for 4, intermediate for 7, high for 2 patients, Euro score was low for 7, intermediate for 5 and high for 1, Eutos LTS score was low for 10, intermediate for 2 and high for 1. Patients were harbouring a "conventional" Philadelphia chromosome without clonal evolution (20-28 metaphases analysed/patient) at diagnosis. All patients were harbouring a Major BCR-ABL transcript. The median BCR-ABL transcript level was 109 (range 35-440) % at diagnosis. Blood pressure was normal in all patients at diagnosis except one. Ponatinib was initiated in all patients at 45 mg daily after a median of 1.5 (range 0.8-2.75) months after diagnosis. Median Ponatinib duration was 4 (range 0.5-6.3) months. Complete Hematologic Response was obtained in 0.98 (range 0.5-1) month in all patients. At 3 months, median BCR-ABL ratio was 0.19 (range 0.008-2.74) %, all patients being in early molecular response (EMR) and 4 patients being already in major molecular response (MMR). Median Ponatinib dose at cessation was 45 (range 0-45) mg daily. IM was started at 400 mg daily in all patients after a median of 1 (range 1-35) day after Ponatinib cessation and after a median of 4 (range 0.54-6.54) months after Ponatinib initiation.

The median BCR-ABL transcripts at 3, 6, 12, 18, 24, 30, 36 and 42 months of Ponatinib (i.e. after a median time of 7, 10, 16, 22, 28, 34, 40 and 46 months of IM) were 0.22 (range 0.01-27)%, 0.08 (0.005-8.99)%, 0.08 (0.01-2.01)%, 0.1 (0.003-1.9)%, 0.03 (0.001-1.61)%, 0.01 (<0.001-0.21)%, 0.01 (0.001-0.21) and 0.01 (0.001-0.02) respectively (see figure 1). On the 10 evaluable patients for molecular analyses, at Ponatinib cessation 40% of patients were >MMR, 40% of patients in MMR, 20% in MR4. At last follow-up, on IM400 10% of patients were in >MMR, 40% in MMR, 20% in MR4, 10% in MR4.5 and 20% in MR5, i. e. 50% in deep molecular response.

At last follow-up, all patients were alive, still on IM400 daily for 32 (27.75-37.4) months, except 4 [1 grade 3 asthenia (now on Dasatinib), 2 molecular failure (now on Dasatinib and Bosutinib)], 1 free of treatment]. None of the patients progressed towards advanced phases to date. No thrombotic events occurred in any of the patients on Ponatinib. Three patients developed hypertension on Ponatinib requiring treatment, still ongoing at last follow-up in all.

Conclusion

The use of Imatinib after Ponatinib first-line therapy for chronic phase CML patients is safe. Despite a significant tyrosine kinase inhibition inferior activity in vitro, it allows the maintenance or the improvement of molecular responses throughout time and serves as a consolidation therapy. These data might pave the way for the design of future clinical trials using Ponatinib in the front-line setting in conjunction with Ponatinib dose reduction.

Figure 1

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Figure 1

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