Hyper-CVAD and Sequential Blinatumomab in Adults with Newly Diagnosed Philadelphia Chromosome-Negative B-Cell Acute Lymphoblastic Leukemia: Results from a Phase II Study

Background: For patients (pts) with Philadelphia chromosome (Ph)-negative B-cell acute lymphoblastic leukemia (ALL), combination chemotherapy achieves complete remission rates of 80-90%; however, many pts ultimately relapse, leading to a cure rate of only 40-50%. Blinatumomab is highly effective in both the relapsed/refractory setting and for eradication of measurable residual disease (MRD). We hypothesized that early incorporation of blinatumomab in pts with newly diagnosed Ph-negative B-cell ALL would decrease the need for intensive chemotherapy, lead to deeper and more durable responses, and improve survival.

Methods: Pts 14-59 years of age with newly diagnosed Ph-negative pre-B-cell ALL, including pts who had received no more than 1 prior cycle of chemotherapy, were eligible. Pts were required to have a performance status of ≤3, total bilirubin ≤2 mg/dl and creatinine ≤2 mg/dl. Pts received hyper-CVAD alternating with high-dose methotrexate and cytarabine for up to 4 cycles, followed by 4 cycles of blinatumomab at standard doses. Pts with CD20+ disease (≥1% cells) received 8 doses of ofatumumab (2000 mg) or rituximab (375 mg/m²). Eight administrations of prophylactic IT chemotherapy were given in the first 4 cycles. Maintenance was with alternating blocks of POMP (given in maintenance cycles 1-3, 5-7, 9-11, and 13-15) and blinatumomab (given in maintenance cycles 4, 8, and 12). After 2 pts with high-risk features experienced early relapse prior to blinatumomab administration, for pts #10+ the protocol was amended so that pts with high-risk disease features (e.g. CRLF2+ by flow cytometry, complex karyotype, KMT2A rearranged, low-hypodiploidy/near triploidy, TP53 mutation, or persistent MRD) started blinatumomab after 2 cycles of hyper-CVAD.

Results: 39 pts have been treated, 34 of whom are evaluable for efficacy (5 too early for assessment). 6 pts were in complete remission (CR) at enrollment and unevaluable for morphologic response. Pt characteristics of the 34 evaluable pts are summarized in Table 1. Median age was 36 years (range, 17-59 years). At least one high-risk feature was present in 19 pts (56%), including TP53 mutation in 27%, CRLF2+ in 20%, and an adverse-risk karyotype in 26%. 82% of pts received ofatumumab or rituximab.

Among 28 pts with active disease at study entry, 100% achieved CR, with 82% achieving CR after the first cycle. MRD negativity by 6-color flow cytometry was achieved in 20/23 responding pts (87%) after 1 cycle and 33/34 pts (97%) overall. There were no early deaths, and the 60-day mortality rate was 0%.

With a median follow-up of 22 months (range, 1-40 months), the 2-year continuous remission and OS rates were 79% and 86%, respectively (Figure 1). Overall, 5 pts (15%) relapsed, 12 (35%) underwent allogeneic SCT in first remission (including 1 additional pt who relapsed post-SCT), and 17 (50%) remain in continuous remission and are currently on treatment or have completed maintenance. All relapses occurred in pts with established poor-risk features, including 2 pts with KMT2A rearrangement, 2 pts with TP53 mutation (1 of whom was low hypodiploid), and 1 pt with baseline WBC count of 32 x 10⁹/L. Two of these relapses occurred during hyper-CVAD cycles before the amendment allowing for earlier integration of blinatumomab for pts with high-risk disease features.

Treatment was overall well-tolerated. Four pts developed grade 2-3 cytokine release syndrome (grade 2, n=3; grade 3, n=1) which resolved with corticosteroids and interruption of blinatumomab. Overall, 14 (41%) pts had a neurological AE of any grade due to blinatumomab. Only one pt discontinued blinatumomab due to blinatumomab-related adverse event (grade 2 encephalopathy and dysphasia).

Conclusion: Sequential combination of hyper-CVAD and blinatumomab is highly effective as frontline treatment of Ph-negative B-cell ALL, with a CR rate of 100% and 97% of pts achieving MRD negativity. Survival data are promising with an estimated 2-year OS of 86%, which compares favorably to historical controls. This study continues to accrue pts.