Impact of Inotuzumb Ozogamicin on Outcome in Relapsed or Refractory Acute B-Lymphoblastic Leukemia Patients Prior to Allogeneic Hematopoietic Stem Cell Transplantation

Background: The outcome of patients with relapsed or refractory (r/r) acute lymphoblastic leukemia (ALL) is poor. At present, allogeneic hematopoietic stem cell transplantation (allo-HCT) is considered the only curative option for patients with r/r B-ALL with best outcomes achieved after effective salvage re-induction therapy and transplantation in complete remission (CR). Veno-occlusive disease, also known as sinusoidal obstruction syndrome (VOD/SOS), is a potentially life-threatening complication of allo-HCT. Inotuzumab ozogamicin (INO) is a humanized anti-CD22 monoclonal antibody conjugated to calicheamicin, developed as a targeted therapy for B-cell malignancies. Rate of VOD/SOS is increased after therapy with INO.

Aims: To characterize a series of relapsed/refractory (r/r) ALL patients (pts) and evaluate outcome after treatment with INO prior to allo-HCT, particularly with respect to risk of VOD/SOS.

Methods: We studied 25 r/r pts (median age, 34 years; range, 16-64 years), who were treated with INO between 2016 and 2022 within a compassionate use program (n=7) or in-label after EMA approval (n=18) One of the 25 pts were previously treated with tyrosine kinase inhibitors for chronic myeloid leukemia and progressed to blast crisis of B-lymphoid lineage. All 25 pts were CD22 positive at relapse/progressive disease. Up to 4 INO cycles (≤2 cycles, n=22; 3-4 cycles, n=3) were administered according to the previously approved regimen.

Results: At the time of r/r B-ALL median white blood cell and platelet counts were 47.1/nl (range, 1.3-300/nl) and 33.5/nl (range, 5-313/nl), respectively. Five pts (20%) were female; ECOG was ≤ 2 in all pts. Cytogenetic analysis at the time of r/r EM-ALL was available in 14 pts. Six pts displayed a t(9;22), 6 had a normal karyotype, 1 was complex and 1 had a deletion 6q as well as trisomy 13. Seventeen (68%) patients achieved CR after the first INO cycle. Prior to allo-HCT, 17 (68%) pts achieved CR, 3 (12%) a partial remission, 4 (16%) were refractory and one (4%) relapsed after CR achievement.

Median follow-up was 41.6 months (95%-CI, 31.1-NR) and median overall survival (OS) was 9.0 months (95%-CI, 5.78-RD months; Figure 1). One- and two-years OS rates were 45.2% (95%-CI, 28.8-70.8%) and 40.7% (95%-CI, 24.8-66.7%), respectively. VOD/SOS after allo-HCT occurred in 7 (28%) pts. Of those, 5 pts died due to VOD and multi-organ failure, all had received ≤2 INO cycles. Risk factor for VOD/SOS was allo-HCT during first-line therapy (p=0.05), whereas age, gender, donor, dose intensity of conditioning or remission status before allo-HCT had no impact. Relapse/progressive disease occurred in eight (32%) pts and all pts succumbed of their disease. Cumulative incidences of relapse/progression or death after 12 months were 20.7% (standard error,E 8.5%) and 32.7% (standard error, 9.8%). Eight (32%) pts died in remission and nine (36%) pts are in ongoing CR.

Conclusions: This outcome analysis demonstrates that treatment with INO is an effective approach with successful bridge-to-transplant. However, risk of VOD/SOS is high, necessitating continuous monitoring and recognition of VOD/SOS risk factors.

Levis:Astellas, and FujiFilm: Research Funding; AbbVie, Amgen, Astellas, Bristol Myers Squibb, Daiichi-Sankyo, FujiFilm, Jazz Pharmaceuticals, and Menarini: Consultancy. Schlenk:AstraZeneca: Research Funding; Pfizer: Honoraria, Research Funding; Abbvie: Research Funding; BergenBio: Honoraria; Novartis: Honoraria; PharmaMar: Research Funding; Daiichi Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Papayannidis:Abbvie: Honoraria; Amgen: Honoraria; Astellas: Honoraria; Pfizer: Honoraria; Novartis: Honoraria; Blueprint: Honoraria; Incyte: Honoraria; GlaxoSmithKline: Honoraria; Bristol Myers Squibb: Honoraria.