[Analysis of 8 children with TCF3:: HLF fusion gene positive acute lymphoblastic leukemia]

Objective: To summarize the clinical characteristics and key points of diagnosis and treatment in children with TCF3::HLF fusion gene-positive acute lymphoblastic leukemia (ALL). Methods: A case series study was conducted. Clinical data of 8 children diagnosed with TCF3::HLF positive ALL at the Hematology Center of Beijing Children's Hospital, Capital Medical University and the Hematology Oncology Department of Henan Children's Hospital between January 2019 and January 2024 were collected. Descriptive analysis was performed on their clinical features, laboratory findings, treatment regimens and prognosis. Results: The cohort included 8 children (3 males and 5 females) with the age of 5.5 (3.5, 7.0) years. Bone pain was the primary clinical manifestation in 4 cases, with multi-site skeletal involvement in 4 cases, hypercalcemia in 5 cases, and coagulation abnormalities in 6 cases. Immunophenotyping revealed common B-cell lineage with myeloid markers in 7 cases and common B-cell phenotype in 1 case. All 8 children were positive for the TCF3::HLF fusion gene. Regarding treatment, 1 case abandoned therapy after diagnosis, while the remaining 7 cases received chemotherapy following the Chinese Children's Leukemia Group-ALL2018 high-risk protocol. Only 1 case achieved minimal residual disease (MRD) negativity by day 33 of induction therapy. Among the 3 cases with MRD negativity before consolidation therapy, 1 case achieved it via conventional chemotherapy, while 2 cases required additional agents (venetoclax or blinatumomab). One case failed to achieve MRD negativity after consolidation therapy and later discontinued treatment (survival periods: 7months).Of the 4 cases who achieved MRD negativity after consolidation, 2 cases received conventional chemotherapy and 2 cases achieved negativity following chimeric antigen receptor T-cell therapy (CART). All 4 cases underwent hematopoietic stem cell transplantation (HSCT). Two cases in the CART combined with HSCT group survived as of the last follow-up (survival periods: 22 and 13 months). In the conventional chemotherapy combined HSCT group, 1 case relapsed and died (survival: 38 months), and 1 case died from transplant complications (survival: 11 months). The other 2 cases achieved MRD negativity before consolidation therapy but did not receive regular subsequent chemotherapy. After MRD recurrence, they underwent CART therapy without HSCT and remained alive at the last follow-up (survival periods: 49 and 12 months). Conclusions: Children with TCF3::HLF positive ALL often present with bone destruction accompanied by hypercalcemia and coagulopathy at initial diagnosis. This subtype of ALL shows poor response to conventional chemotherapy regimens, characterized by low early remission rates and high relapse risk even after HSCT. Better therapeutic outcomes have been observed with small molecule targeted drugs, immunotherapy and CART therapy.