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2827 Rescuing of the Chemotherapy Sensitivity in Relapsed/Refractory, Pediatric Acute Lymphoblastic Leukemia (r/r ALL) through the Combination of Navitoclax (NAV) and Venetoclax (VEN): Results of Compassionate Use across Four European Countries

Program: Oral and Poster Abstracts
Session: 613. Acute Lymphoblastic Leukemias: Therapies Excluding Allogeneic Transplantation: Poster II
Hematology Disease Topics & Pathways:
Combination therapy, Treatment Considerations
Sunday, December 8, 2024, 6:00 PM-8:00 PM

Francesca Del Bufalo, MD, PhD1*, Andrej Lissat, MD, PhD2*, Chiara Rosignoli, MD1*, Veerle Mondelaers, MD3*, Christophe Chantrain, MD, PhD4*, Jochen Büchner, MD, PhD5*, Roberto Carta, MD1*, Marco Becilli, MD1*, Jonas Eggeling, MD2*, Federica Galaverna, MD, PhD1*, Stefania Gaspari, MD1*, Maria Giuseppina Cefalo, MD1*, Arend von Stackelberg, MD2* and Franco Locatelli, MD1,6

1Department of Hematology-Oncology and Cell and Gene Therapy, IRCCS Bambino Gesù Children's Hospital, Rome, Italy
2Department of Hematology and Oncology, Charité Universitätsmedizin Berlin, Berlin, Germany
3Department of Pediatric Hematology-Oncology and Stem Cell Transplantation, UZ GENT, Ghent, BEL
4Division of Pediatric Hematology-Oncology, Centre Hospitalier Chrétien (CHC), MontLégia, Liege, Belgium
5Oslo University Hospital, Oslo, Norway
6Catholic University of the Sacred Heart, Rome, Italy

Despite improving survival rates of children and young adults with relapsed/refractory ALL, a significant number of patients still dies from relapsed and refractory (R/R) disease. This calls for combinations of new drugs to reinduce complete remissions (CR) and offer the possibility of long-term survival through consolidation with either allogeneic hematopoietic stem cell transplantation (allo-HSCT) or chimeric antigen receptor (CAR)-T cells. Whereas immunotherapies, including CAR-T cells, have increased the proportion of patients with B-ALL who are cured, the results for T-ALL are preliminary and data of long-term outcome in larger patient cohorts are not available yet. In addition, CAR T cells are associated with significantly improved survival if administered with low disease burden, a result that may be difficult to achieve in patients with advanced disease. B-cell lymphoma (BCL) family proteins have a key role in regulating the apoptotic response of blasts to the chemotherapy-induced damage. A Phase I study suggested that the combination of the BCL2 and BCL-XL/BCL2 inhibitors (VEN and NAV, respectively) with conventional chemotherapy could revert the resistance observed in r/r leukemia patients.

We retrospectively collected safety and efficacy data of VEN/NAV combined with chemotherapy in pediatric patients and young adults with r/r ALL treated under compassionate use in 5 European centers. Between 08/2021 and 04/2024, 30 children/young adults with B-ALL (n=17) or T-ALL (n=13) were treated. Eight B-ALL patients and 12 with T-ALL were male, the median age was 7 (range 3-19) and 10 (3-17), respectively. All patients were heavily pretreated, having received a median of 3 previous lines of therapy in both cohorts (range: 2-7, B-ALL; 1-5, T-ALL); 9 B-ALL patients and 5 T-ALL relapsed after allo-HSCT. Extramedullary sites were involved in 12/17 patients with B-ALL (including 3 CNS) and 4/13 T-ALL (4 CNS). Unfavorable cytogenetics characteristics were present in 6/17 B-ALL patients and 4/13 T-ALL patients.

NAV and VEN were administered continuously over 28 days in combination with different chemotherapy backbones. In B-ALL patients, dexamethasone and vincristine were administered in 15/17 children (alone – 8/15; in combination with PEG-asparaginase – 5/15; or with anthracyclines – 2/15). In patients with T-ALL, the chemotherapy backbones were more heterogeneous including citarabine in 8/13, daratumumab in 5/13, tyrosine kinase inhibitors in 4/13 and decitabine in 3/13 patients. The median number of NAV/VEN cycles administered was 1 (0.3 – 3). The main reasons for treatment discontinuation were: treatment failure (44.4%), consolidation with allo-HSCT/CAR-T cells (48.1%) or prolonged severe hematological toxicity (7.4%).

The most common toxicity was hematologic: overall, 93% of the patients developed grade 3-4 neutropenia, 67% grade 3-4 anemia and 81.5% grade 3-4 thrombocytopenia. Two patients developed bacterial sepsis during treatment-induced aplasia. Other severe toxicities were: paralytic ileus (14.8%), salt wasting tubulopathy (11.1%) and pancreatitis (7.4%). No fatal adverse event was recorded.

The overall response rate was 71% for the B-ALL cohort (12/17 patients) and 50% for the T-ALL cohort. In particular, in the B-ALL patients, 11/16 patients obtained CR in the BM (1 patient had EM isolated disease) and 10/12 in the EM compartment. Amongst T-ALL patients, 12/13 children were evaluable for response and 5/12 (42%) demonstrated CR in the bone marrow. Twelve patients in the B-ALL cohort and 4/12 in the T-ALL cohort received further consolidation with allo-HSCT and/or CAR-T cells. Five B-ALL patients and 2 T-ALL patients are alive and maintain the response, with a median follow-up of 24 months and 25 months, respectively. All patients who did not receive consolidation ultimately relapsed and died of disease.

Our experience underlines the strong potential of the combination of VEN/NAV with conventional chemotherapy to reinduce complete remission in heavily pretreated and refractory pediatric/young adult patients with either B- or T-ALL, offering a bridge to consolidative strategies that induce long term remission of these patients. The approach deserves further investigation of its full potential in a prospective clinical trial and in less advanced disease cohorts of patients, despite the recent announcement of discontinuation of development of NAV by the Company.

Disclosures: Büchner: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees.

*signifies non-member of ASH