Nilotinib (Tasigna^®) and Low Intensity Chemotherapy for First-Line Treatment of Elderly Patients with BCR-ABL1-Positive Acute Lymphoblastic Leukemia: Final Results of a Prospective Multicenter Trial (EWALL-PH02)

Background. Tyrosine kinase inhibitors (TKI) are standard front-line therapy for patients with BCR-ABL1/Philadelphia positive ALL (Ph+ ALL), but the relative merits of available TKIs remain uncertain. Nilotinib is a potent inhibitor of BCR-ABL1 with broader activity against ABL kinase domain mutations than imatinib and greater selectivity than dasatinib or ponatinib. As there is a paucity of data on nilotinib as first-line therapy for Ph+ ALL, the EWALL (European Working Group for Adult ALL) conducted an international clinical trial to evaluate efficacy and safety of the combination of nilotinib with low intensity chemotherapy.

Patients and Methods. After a prephase with dexamethasone (DEX) and cyclophosphamide, nilotinib (400 mg BID) was given concurrently with the same chemotherapy backbone employed in the EWALL-PH01 assessing the combination with dasatinib (Rousselot et al, Blood 2016;128:774-82). Induction consisted of nilotinib combined with weekly vincristine (VCR, 1mg iv) and oral dexamethasone 40mg 2 days (20 mg over 70y). Nilotinib was continued throughout six consolidation cycles, followed by 24 months maintenance therapy with nilotinib, 6-MP, MTX and DEX/VCR boosts. Stem cell transplantation (SCT) was permitted as considered appropriate. BCR-ABL1 RTQ-PCR and kinase domain resistance mutations were centrally monitored. Primary endpoint was event-free survival (EFS) at 12 months, secondary endpoints included rates of CR, major and complete molecular response, relapse free survival (RFS), EFS and overall survival (OS).

Results. 72/79 enrolled pts. were evaluable for response, 3 withdrew consent, 4 did not meet eligibility criteria. Median age was 65.5 (55-85) years, male/female ratio 0.85, ECOG status 0 or 1 in 89% of pts., median CIRS comorbidity score 5(0-19). Baseline vascular risk factors including high blood pressure (grade ≥2) were present in 36% of pts.. Sixty-eight of 72 pts. (94.4%) achieved CR, one died during induction and one was refractory, 2 pts. discontinued study therapy. Non-hematologic adverse events (AE) grades 3/4 during induction (in ≥ 5% of pts. irrespective of causality) included infections (n=20), elevated transaminases or bilirubin (n=18) and gastrointestinal AEs (n=12). The spectrum of AEs was similar during consolidation, without concerns related to cardiovascular events. 24 pts. (61y; 55-69y) underwent allogeneic (9 MUD, 12 SIB, 3 Haplo) and 3 autologous SCT. 21 pts. received reduced intensity conditioning (including 8Gy TBI, n=11) regimens. Among all pts., relapse was the main cause of treatment failure (n=23; 17 BM, 2 CNS, 3 other sites, 1 na), 11 pts. died in CR (6 after HSCT), 34 are in ongoing CR. Based on Kaplan Meier analysis, EFS (events being resistant disease, relapse or death) at 12 months was 74%, with median follow-up of 39 (24-66) months for surviving pts., EFS and OS at 4 years was 42%, and 47%, respectively. By landmark analyses using median time to HSCT as cutoff, cumulative incidence of relapse in transplanted vs. non-transplanted pts. was 32% and 47%, OS at 4 years was 61% and 39%, median OS was not reached versus 3.6 years, respectively (p=ns). The proportion of pts. with a BCR-ABL1/ABL1 ratio ≤0.1% increased from 41% after induction to 86% after consolidation 2; that of pts. with undetectable or non-quantifiable BCR-ABL1 transcripts (sensitivity ≥10^-4) increased from 14% to 58%.

Conclusions. Nilotinib combined with low-intensity chemotherapy is well tolerated and highly effective in elderly pts. with Ph-positive ALL. OS and EFS compare favorably with previous similar studies testing imatinib or dasatinib. With 32% of pts. undergoing allogeneic HSCT and 61% survival at 4 years, transplantation is a viable option in this elderly cohort of pts..