Imatinib Significantly Enhances Long-Term Outcomes In Philadelphia Positive Acute Lymphoblastic Leukaemia; Final Results of the UKALLXII/ECOG2993 Trial
Authors: Fielding Adele K. , Buck Georgina , Lazarus Hillard M. , Litzow Mark R. , Luger Selina , Marks David I. , McMillan Andrew , Moorman Anthony V. , Paietta Elisabeth , Richards Susan M , Tallman Martin S. , Rowe Jacob M. , Goldstone Anthony H. 
Published: October 2019

Abstract 169

The Philadelphia positive (Ph+) arm of the international adult acute lymphoblastic leukaemia (ALL) trial UKALL12/ECOG2993 opened in 1993 and is the largest single study of patients with Ph+ ALL, with a total of 441 participants. The first cohort of study patients was treated prior to Imatinib (N=266 “Pre Imatinib“) with 2 phases of induction therapy given over 2 months followed by matched sibling or unrelated donor myeloablative allogeneic haematopoietic stem cell transplant (alloHSCT) whenever possible. The treatment protocol and outcome for these patients has been published (Fielding et al, Blood 2009). Beginning March 2003, a second cohort of study patients had Imatinib 600mg daily added, as a consolidation block after the second induction chemotherapy, (N=86, “Late Imatinib”). From late 2005, a final cohort within the trial were given Imatinib earlier, in conjunction with the second phase of induction (N=89, “Early Imatinib”). Patients in both Imatinib cohorts resumed the drug for a further 2 years following alloHSCT, if tolerated. If alloHSCT was not possible, Imatinib was permitted for 2 years, with maintenance. The trial closed to recruitment in December 2006 (USA) and October 2008 (UK). All except 8 patients have now completed therapy. An earlier analysis of these data did not indicate a clear long-term advantage to receiving Imatinib.

We now report 3-year follow-up, which shows large outcome differences between the 3 groups. There were no pre-existing differences between the 3 cohorts in terms of gender, presenting white blood cell counts and presence of central nervous system disease at diagnosis. However, the Pre-Imatinib cohort was younger than the two Imatinib cohorts, due to an increase in the upper age limit for study entry.

Percentage complete remission (CR) rates and survival of induction therapy are shown in table 1. The total CR rate for the imatinib cohorts was significantly higher than for the pre-imatinib cohort (p=0.004).

Table 1 Pre-Imatinib With Imatinib N=266 Total With Imatinib N=175 Part 1 Late Imatinib N=86 Part 2 Early Imatinib N=89 Died in induction<d56 5 5 3 7 Survived induction but never achieved remission 13 3 5 1 Total not achieving CR 18 8 8 8 CR on protocol induction 67 77 73 80 Total CR rate (includes those achieving remission later than post induction) 82 92 92 92

Pre- Imatinib, only 28% of patients went on to receive alloHSCT as per protocol. With any Imatinib, 44% of patients received alloHSCT as per protocol.

Survival outcomes of patients in the 3 cohorts are shown in the table 2. Overall survival (OS), event free survival (EFS) and relapse free survival (RFS) are all at 3 years with 95% confidence intervals (CI) shown in brackets. The P values are for two comparisons - ** denotes the comparison between patients receiving any Imatinib and patients receiving none and ^ denotes the comparison between the Early and Late Imatinib cohorts.

Table 2 Pre-Imatinib With Imatinib Total With Imatinib Part 1 Late Imatinib Part 2 Early Imatinib % OS (95% CI) (see also Figure 1) 25 (20–30) 42 (34–49) 34 (24–44) 48 (36–60) p=0.0001** p=0.05^ % EFS (95% CI) 19 (14–24) 36 (29–44) 29 (19–38) 45 (34–56) p=0.0001** p=0.04^ % RFS (95% CI) 36 (28–43) 54 (45–63) 45 (33–57) 62 (50–75) p=0.0001** p=0.02^

Figure 1 Three-year OS for patients who received per protocol alloHSCT was 59% vs. 28% (with no plateau on the curve) for those who did not receive alloHSCT as per protocol. By comparison, pre-imatinib, 5 year OS was 40% for transplanted- and 19% for non-transplanted patients. Hence, the extent to which Imatinib without subsequent alloHSCT can improve the outcome for adult Ph+ ALL is not yet clear. Figure 1. Three-year OS for patients who received per protocol alloHSCT was 59% vs. 28% (with no plateau on the curve) for those who did not receive alloHSCT as per protocol. By comparison, pre-imatinib, 5 year OS was 40% for transplanted- and 19% for non-transplanted patients. Hence, the extent to which Imatinib without subsequent alloHSCT can improve the outcome for adult Ph+ ALL is not yet clear.

In conclusion, receiving any Imatinib during induction for Ph+ ALL significantly enhances CR rate and increase alloHSCT rate. This translates into a highly significant EFS, OS and RFS advantage to receiving Imatinib during therapy. An earlier start to Imatinib is significantly better than a later start. Though comparisons between study cohorts are not randomised, the large differences seen are unlikely to be explained by factors other than treatment. There can be no basis for omitting Imatinib from the initial therapy of adult patients with Ph+ ALL. However, our data show that the best outcome is seen when patients receive Imatinib followed by myeloablative alloHSCT, where nearly 60% of such patients survive 3 years from diagnosis.

Disclosures:

Goldstone: Roche: Honoraria, Speakers Bureau.