Photo courtesy of Amgen
Vials of blinatumomab powder and solution for infusion
Blinatumomab proved more effective than chemotherapy in a phase 3 trial of adults with Ph-negative, relapsed/refractory B-cell precursor acute lymphoblastic leukemia (B-ALL).
Blinatumomab produced higher remission rates and nearly doubled overall survival (OS) when compared to standard care, which encompassed 4 different chemotherapy regimens (investigator’s choice).
The incidence of grade 3 or higher adverse events (AEs) was higher for patients who received chemotherapy, but the incidence of serious AEs was higher in the blinatumomab arm.
These results were published in NEJM. The trial, known as TOWER, was sponsored by Amgen, the company developing blinatumomab.
“Results from the TOWER study reinforce the potential of this single-agent, bispecific T-cell engager immunotherapy, which helped a higher percentage of patients achieve minimal residual disease response versus standard of care chemotherapy, highlighting the depth and quality of remissions achieved,” said study author Hagop M. Kantarjian, MD, of The University of Texas MD Anderson Cancer Center in Houston.
Treatment
TOWER enrolled 405 patients with Ph-negative, relapsed/refractory B-ALL, 376 of whom ultimately received treatment.
The patients received blinatumomab (n=267) or investigator’s choice of 1 of 4 protocol-defined standard chemotherapy regimens (n=109):
- FLAG (fludarabine, high-dose cytarabine arabinoside, and granulocyte-colony stimulating factor), with or without an anthracycline (n=49, 45%)
- A high-dose cytarabine arabinoside-based regimen (n=19, 17%)
- A high-dose methotrexate-based regimen (n=22, 20%)
- A clofarabine-based regimen (n=19, 17%).
Patients who received blinatumomab received it as a continuous infusion, 4 weeks on and 2 weeks off, at 9 µg/day for 7 days, then 28 µg/day on weeks 2-4. They received 2 cycles of induction, which was followed by 3 cycles of consolidation if they had ≤5% blasts.
If patients still had ≤5% blasts after consolidation, they received up to 12 months of blinatumomab maintenance. Maintenance was a continuous infusion, 4 weeks on and 8 weeks off, at 28 µg/day.
Patients in the blinatumomab arm received a median of 2 cycles of therapy (range, 1-9). And patients in the chemotherapy arm received a median of 1 cycle (range, 1 to 4).
Thirty-two percent of patients in the blinatumomab arm received consolidation, as did 3% of patients in the chemotherapy arm.
Patients
Patient characteristics were similar between the treatment arms. The mean age was 41 in both arms (range, 18-80). Nearly 60% of patients in both arms were male.
About 40% of patients in the blinatumomab arm and 50% in the chemotherapy arm had not received any prior salvage regimens.
Thirty-five percent of patients in the blinatumomab arm and 34% in the chemotherapy arm had an allogeneic hematopoietic stem cell transplant (allo-HSCT) prior to study enrollment. Seventeen percent and 20%, respectively, relapsed after HSCT.
Forty-two percent and 40%, respectively, were refractory to primary or salvage therapy. Twenty-eight percent of patients in both arms were in their first relapse, and their first remission had lasted less than 12 months. Twelve percent of patients in both arms had an untreated second or greater relapse.
Remission
Within 12 weeks of treatment initiation, complete remission (CR) rates were significantly higher in the blinatumomab arm than the chemotherapy arm. (This was in the intent-to-treat population, which included 271 patients in the blinatumomab arm and 134 patients in the chemotherapy arm.)
The rate of CR with full hematologic recovery was 34% in the blinatumomab arm and 16% in the chemotherapy arm (P<0.001). The rate of CR with full, partial, or incomplete hematologic recovery was 44% and 25%, respectively (P<0.001).
Among patients who achieved a CR with full, partial, or incomplete hematologic recovery, 76% of those in the blinatumomab arm and 48% of those in the chemotherapy arm were negative for minimal residual disease.
Survival
At a median follow-up of 11.7 months for the blinatumomab arm and 11.8 months for the chemotherapy arm, the OS was significantly longer in the blinatumomab arm.
The median OS was 7.7 months and 4.0 months, respectively (hazard ratio for death=0.71, P=0.01).
The improvement in OS with blinatumomab was consistent across subgroups, regardless of age, prior salvage therapy, or prior allo-HSCT.
The investigators also considered the effect that post-treatment allo-HSCT might have on OS. Sixty-five patients in the blinatumomab arm and 32 in the chemotherapy arm went on to receive an allo-HSCT (24% of patients in both arms).
When the investigators censored for post-treatment allo-HSCT, the median OS was 6.9 months in the blinatumomab arm and 3.9 months in the chemotherapy arm (hazard ratio=0.66, P=0.004).
Safety
Nearly all patients in both arms (99%) experienced AEs. Grade 3 or higher AEs occurred in 87% of patients in the blinatumomab arm and 92% of those in the chemotherapy arm. Serious AEs occurred in 62% and 45%, respectively.
Grade 3 or higher AEs of interest, according to the researchers, were infection (34% with blinatumomab and 52% with chemotherapy), neutropenia (38% and 58%, respectively), elevated liver enzymes (13% and 15%, respectively), neurologic events (9% and 8%, respectively), cytokine release syndrome (5% and 0%, respectively), infusion reactions (3% and 1%, respectively), and lymphopenia (2% and 4%, respectively).
Fatal AEs occurred in 19% of patients in the blinatumomab arm and 17% of those in the chemotherapy arm.
Fatal AEs that occurred in at least 1% of patients in either arm (blinatumomab and chemotherapy, respectively) were sepsis (3% and 4%), septic shock (2% and 0%), multiorgan failure (1% and 0%), respiratory failure (<1% and 2%), and bacteremia (0% and 2%).