Abstracts Clinical Lymphoma, Myeloma & Leukemia September 2023 S246 ALL-301 Hematopoietic Stem Cell Transplantation From HLA‑Matched Sibling Donors in Children With Acute Lymphoblastic Leukemia: A Report From the Children’s Cancer Hospital in Egypt Mahmoud Hammad MD1, Hanafy Hafez MD1, Iman Sidhom MD1, Dina Yassin MD2, Sherine Salem MD2, Khaled Alsheshtawi MD3, Nayera Hamdy MD2, Nahla Elsharkawy MD2, Alaa Elhaddad MD1 1Paediatric Oncology Department National Cancer Institute, Cairo University and Children’s Cancer Hospital Egypt, Cairo, Egypt. 2Clinical Pathology Department National Cancer Institute, Cairo University and Children’s Cancer Hospital Egypt, Cairo, Egypt. 3Children’s Cancer Hospital Egypt, Cairo, Egypt Context: Allogeneic hematopoietic stem cell transplantation (HSCT) is widely used for high-risk acute lymphoblastic leukemia (ALL) patients in their first complete remission (CR1) and for relapsed patients in their second complete remission (CR2). Objective: We aimed to describe the outcomes (overall survival [OS], event-free survival [EFS], and non-relapse mortality [NRM]) and relapse probabilities in a group of pediatric ALL patients who had undergone HSCT in CR1 or CR2 from matched sibling donors (MSDs) using myeloablative conditioning (MAC) regimens. We further aimed to determine outcome differences in relation to indications for HSCT in patients transplanted in CR1. Patients and Methods: We retrospectively analyzed data for 67 children with ALL from a cancer center in a low/middle-income country who had undergone HSCT from human leukocyte antigen (HLA)-MSDs using MAC regimens between 2007 and 2020. We described the survival outcome and relapse probability after achieving CR1 and CR2 and determined outcome differences in relation to indications for HSCT in patients transplanted in CR1. All patients had achieved a negative minimal residual disease prior to transplant (<0.01%). Results: Forty-six patients (68.7%) were in CR1; 25 had adverse cytogenetics, including 18 patients with Philadelphia chromosomepositive ALL (Ph-positive ALL), and 21 had poor induction response. The 5-year OS, EFS, and cumulative incidence of relapse (CIR) for the whole cohort were 56.1% (95% CI, 42.8%-69.4%), 49% (95% CI, 35.7%-62.3%) and 33.5% (95% CI, 21.7%- 45.8%), respectively with better EFS and CIR in CR1 transplants compared to CR2 transplants (P=.02 and P=.03, respectively). Patients with Ph-positive ALL had better 5-year OS, EFS, and NRM compared with other CR1 transplants (P=.015, P=.009, and P=.028, respectively). Conclusion: HSCT from MSD for ALL in the CR1 group had superior outcomes compared to the CR2 group and was apparently a curable option for Ph-positive ALL without an increased risk of non-relapse mortality. Poorer survival rates and higher relapse probabilities were associated with HSCT conducted in patients who had a poor response to induction therapy or suffered a relapse. Keywords: ALL, matched sibling donor, hematopoietic stem cell transplantation, acute lymphoblastic leukemia, pediatric, low and middle-income countries ALL-327 Inotuzumab Ozogamicin and Liver Toxicity: Something Old, Something New, and Something to Consider Bryan Pham MD1, Suhani Dalal DO1, Daniel Park DO2, Austin Gray MD1, Kum Ja Lee PharmD1, Mojtaba Akhtari MD1 1Loma Linda University Medical Center, Loma Linda, USA. 2UCSFFresno, Fresno, USA Context: Inotuzumab ozogamicin (InO) is associated with sinusoidal obstruction syndrome (SOS), a potentially fatal complication that occurs frequently, even at higher incidence rates, after hematopoietic stem cell transplantation (HSCT). Currently only approved as prophylaxis for patients undergoing HSCT, ursodeoxycholic acid (UA) has been shown to not only delay the onset of liver toxicity (LT) but also reduce the incidence of SOS. However, SOS can still occur in patients on InO without HSCT, and the utilization of UA in all patients on InO is not a common practice. We report two patients with R/R B-ALL who received InO and developed LT, highly suspicious for SOS. A 42-yearold male with B-ALL, Ph+, who was on ponatinib and InO, had elevated liver enzymes. Hyperbilirubinemia and hyperammonemia were noted, and abdominal ultrasound showed hepatomegaly and portal hypertension, and subsequently, the patient passed away. This patient was on UA. A 29-year-old female with R/R B-ALL Ph- treated with InO also developed hepatosplenomegaly and LT. She was on prophylactic UA, and subsequently, InO was stopped. LFTs normalized, and the patient was started on alternative treatment. Objective: The aim of this case series is to emphasize the significance of LT with InO in patients with R/R B-ALL and to propose a new treatment protocol to reduce the incidence of LT. Methods: Herein, we describe two patients who developed significant LT. Conclusion: Although UA is currently only recommended for patients undergoing HSCT, our case series asserts that the risk of hepatotoxicity is still high regardless of HSCT status. We propose that close monitoring of liver function, avoiding hepatotoxic medications, and utilization of UA prophylaxis in all patients on InO should be considered and that these measures might improve morbidity and mortality and morbidity due to SOS and hepatic injury. Keywords: ALL, inotuzumab, ozogamicin, sinusoidal obstruction syndrome, ursodeoxycholic acid ALL-329 Ph‑Negative Acute Lymphoblastic Leukemia (ALL) in Adolescent and Young Adults: Long‑Term Outcomes After Treatment According to the Adult Strategy RALL Protocol Olga Aleshina MD, PhD1, Ekaterina Kotova MD1, Irina Galtseva MD, PhD1, Galina Isinova MD, PhD1, Anastasia Vasilieva MD1, Sergey Bondarenko MD, PhD2, Alina Antipova MD, PhD3, Olga Baranova MD, PhD3, Elena Borisenkova MD4, Olga Samoilova MD,
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