Inotuzumab ozogamicin then blinatumomab for older adults with newly diagnosed, ph-negative, CD22-positive, B-cell acute lymphoblastic leukemia: Extended follow-up of alliance for clinical trials in oncology A041703 cohort 1 reveals durable remission

Abstract Background: Older adults with newly diagnosed ALL treated with conventional chemotherapy have poor survival due to high rates of toxic death and disease relapse. The Alliance A041703 trial (NCT0373981) tested chemotherapy-free treatment with the anti-CD22 antibody-drug conjugate inotuzumab ozogamicin (InO) followed by the anti-CD19-CD3 bifunctional T-cell engager blinatumomab (blina) without maintenance in older adults to reduce toxicity and increase efficacy of therapy for this patient (pt) population. We previously reported with 22-month (mo) median follow-up that the study met its primary endpoint with a 1-year (yr) event-free survival (EFS) of 75% (90% confidence interval [CI] 63-89% lower bound exceeding null rate of 10%; JCO 2023 41, 7006). Here we report secondary outcomes with 45-mo median follow-up: 3-yr EFS, 3-yr overall survival (OS), response, and relapse characteristics. Methods: Eligible pts were ≥60 yrs old with newly diagnosed, Ph-negative, CD22-positive (≥20% of blasts) B-cell ALL without planned allogeneic HCT (alloHCT), liver disease, or CNS involvement at enrollment. Induction IA was InO 0.8 mg/m2 day (d) 1, 0.5 mg/m2 d8, d15 IV on a 21d cycle. Pts with adequate cytoreduction (marrow blasts reduced ≥50% or marrow cellularity ≤20%) after IA went to IB if in CR/CRi (InO 0.5 mg/m2 d1, d8, d15 IV; 28d cycle) or IC if no CR/CRi (InO 0.8 mg/m2 on d1 and 0.5 mg/m2 on d8 and d15 IV; 28d cycle). Those without cytoreduction to IA started course II blina. Pts without events in IA/B/C received course II blina continuous IV (9 mcg/d x 7d then 28 mcg/d x 21d; 14d break; 28 mcg/d x28d). Pts with CR/CRi to InO received 2 more 28d cycles of blina; others received 3 more. CNS prophylaxis was methotrexate 15 mg intrathecal x 8 doses. EFS was time from therapy start to failure to achieve CR/CRh/CRi by the end of course II, progression, relapse, or death, whichever occurred first, censored at last follow up. OS was time from registration to death from any cause censored at the last known alive date. Results: The median age of the 33 treated pts was 71 yrs (range 60-84). Eight pts had prior therapy for alternate malignancy in CR for >2 yrs prior to enrollment (6 multiple myeloma, 1 non-Hodgkin lymphoma, 1 breast cancer). Median CD22 expression was 92% (range 21-100%) and 49% had NCCN poor-risk genetics. Five pts underwent alloHCT in first CR/CRi and 2 pts received POMP maintenance after early discontinuation of blina (1 toxicity, 1 physician choice). The CR/CRi rate after InO was 85% (1 early death/refractory, 2 refractory, 2 undetermined due to low marrow cellularity on remission assessment marrow) with CR/CRi rate of 97% by completion of course II blina. With 45 mo median follow-up, the estimated 3-yr EFS was 48% (95% CI 33-70%) with a median EFS of 31 mo (95% CI 17.4-not reached [NR]) and no events after 31 mo. Sixteen events occurred: 12 relapses, 1early death, and 3 deaths in remission (1 encephalopathy, 1 relapse of multiple myeloma, 1 pulmonary complications after alloHCT). No isolated CNS relapse has been reported. Among relapses, 10 had immunophenotyping. Four (40%) were CD19-negative, one of which was also CD22-negative. Among CD19-negative relapses, genetics were hypodiploid (2), Pax5alt (1), and ZNF384-like (1, also CD22-negative). TP53 mutation or loss was observed in 5/12 (42%) relapses. Thirteen pts died. The estimated 3-yr OS was 59% (95% CI 44-79%) with median OS NR (95% CI 32-NR) with no deaths after 36 mo. In univariate analysis, EFS and OS were not impacted by age, gender, genetic risk (NCCN), prior therapy for alternate malignancy, or alloHCT in first remission. EFS was better with higher CD22 expression at diagnosis (≥90% vs <90%, 3-yr EFS 60% vs 25%, P=0.044). EFS and OS were worse for detectable minimal residual disease (MRD) at any timepoint by ASO-PCR. Undetectable MRD after course IA (1 cycle InO induction) was associated with EFS with a 3-yr EFS of 52% vs 0% for detectable MRD (median NR vs 8 mo, hazard ratio [HR] 0.07, P=0.004) and a 3-yr OS of 100% vs 0% for detectable MRD (median NR vs 20 mo, HR 0.00, P=0.0014). Conclusions: Longer follow-up of chemotherapy-free treatment with InO and blina for older pts with newly diagnosed, Ph-negative, CD22-positive, B-cell ALL reveals durable remissions and survival. The A041703 regimen is a compelling option for first-line treatment of this pt population. Support: U10CA180821, U10CA18088; https://acknowledgments.alliancefound.org.