A Phase II Study of Dasatinib and Dexamethasone As Primary Therapy Followed By Hematopoietic Cell Transplantation for Adults with Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia: CALGB Study 10701 (Alliance)

Background:

Potent inhibitors of BCR-ABL1have improved remission results and altered post-remission therapy for Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). Dasatinib plus dexamethasone followed by hematopoietic cell transplantation (HCT) promises high response rates, reduced toxicity, and durable remissions.

Methods:

We conducted a Phase II trial at 17 U.S. centers with the primary objective being to estimate the 3-year overall survival and disease-free survival of patients with Ph+ ALL treated with dasatinib and dexamethasone for remission induction and intensification, central nervous system (CNS) prophylaxis, consolidation with reduced-intensity conditioning (RIC) allogeneic HCT, autologous HCT, or etoposide and cytarabine, and dasatinib-based maintenance. Eligible patients had untreated Ph+ ALL, were ≥18 years old, and had normal cardiac function. Induction (Course I) used dasatinib 140 mg oral daily and dexamethasone 10 mg/m²/day oral or intravenous (IV) days 1-7. For patients with ≤20% blasts in the Course I, Day 15 bone marrow biopsy, intensification (course II) continued daily dasatinib with another 7 days of dexamethasone. Those with >20% lymphoblasts also received vincristine (VCR) and daunorubicin (DNR). Patients (n=3) not in CR/CRi after Course II received a second induction (Course III) with dasatinib, cyclophosphamide, VCR, DNR, and dexamethasone. After Course II or III, CNS prophylaxis (Course IV) consisted of IV VCR and IV, oral, and intrathecal methotrexate (MTX). Dasatinib was restarted at serum [MTX] <0.05 microM. Course V consisted of HCT or chemotherapy. Patients aged 18-70 years with an HLA-matched donor underwent RIC allogeneic HCT; otherwise they underwent autologous HCT. Allogeneic HCT conditioning used fludarabine 30 mg/m²/day IV day -7 through -3, alemtuzumab 20 mg/day IV day -7 through -3, and melphalan 140 mg/m² once on day -2. GVHD prophylaxis with tacrolimus began day -2. Patients undergoing autologous HCT received etoposide 10 mg/kg/day (age >65 years, 5 mg/kg/day) continuous IV for 4 days and cytarabine 2 g/m² (age >65 years, 1 g/m²) IV every 12 hours for 8 doses (EA) then G-CSF for mobilization. Autologous HCT conditioning used melphalan 100 mg/m²/day on days -2 and -1. Patients >70 years or unable to undergo HCT received EA alone. Dasatinib maintenance (Course VI) began on day 30 of Course V and continued for 12 months and until 2 consecutively negative bone marrow BCR-ABL1RT-PCR assays 3 months apart or until relapse. Dasatinib levels were measured on day 15 of induction.

Results:

Sixty-six patients enrolled from 12/15/2010 to 11/14/2014; 65 received dasatinib and are evaluable. Median age was 60 years (22-87); 49% were male. Median presenting WBC count was 23.1 x 10³/ul (0.3-453.6). No deaths occurred during induction or intensification. CR or CRi occurred 31 patients (48%) by Day 15 of induction and in 62 patients overall (95%; CR 86%). Median dasatinib levels in serum and CSF on Day 15 of induction were 30.3 ng/mL (<3-308) and 0.29 ng/mL (<0.2-1.37), respectively suggesting approximately 1% of plasma dasatinib penetrates into the CSF, less than the unbound fraction (6%). Fifty-four patients started Course IV, 38 Course V, and 37 Course VI. Fourteen patients continue on protocol therapy. Of 38 patients receiving Course V, 22 had allogeneic HCT, 6 had autologous HCT, and 10 had EA chemotherapy. Median age of allogeneic HCT recipients was 61 years (31-69). Robust autologous stem cell mobilization was observed [median CD34+ cell count, 90 x 10⁶/kg (31-166, n=6)]. Dasatinib maintenance was feasible after allogeneic HCT, autologous HCT, and chemotherapy alone with no missed doses in 59%, 83%, and 63% of cycles, respectively. Ten patients have relapsed with one isolated CNS relapse. No relapses have occurred after allogeneic HCT with 3 relapses after autologous HCT and one after Course V EA alone. Median follow up for survivors is 22.8 months (longest, 51 months). There have been 23 deaths: 5 treatment-related (4 after allogeneic HCT, 1 after course V EA), 16 disease-related and 2 unrelated.

Conclusions:

Dasatinib with dexamethasone yields CR rates comparable to those reported with tyrosine kinase inhibitors combined with conventional chemotherapy. Post-remission therapy with reduced-intensity allogeneic HCT, autologous HCT, or chemotherapy followed by dasatinib maintenance is feasible. Survival follow up is maturing.