B-cell lymphoblastic lymphoma (BCP-LBL) and B-cell acute lymphoblastic leukemia (BCP-ALL) are the malignant counterparts of immature B-cells. BCP-ALL is the most common hematological malignancy in childhood, while BCP-LBL accounts for only 1% of all hematological malignancies in children. Therefore, BCP-ALL has been well studied and treatment protocols have changed over the last decades, whereas treatment for BCP-LBL has stayed roughly the same. Clinical characteristics of 364 pediatric patients with precursor B-cell malignancies were studied, consisting of BCP-LBL (n = 210) and BCP-ALL (n = 154) patients. Our results indicate that based on the clinical presentation of disease, B-cell malignancies probably represent a spectrum ranging from complete isolated medullary disease to apparent complete extramedullary disease. Hepatosplenomegaly and peripheral blood involvement are the most important discriminators, as both seen in 80% and 95% of the BCP-ALL patients and in 2% of the BCP-LBL patients, respectively. In addition, we show that the overall survival rates in this cohort differ significantly between BCP-LBL and BCP-ALL patients aged 1–18 years (p = 0.0080), and that the outcome for infants (0–1 years) with BCP-LBL is significantly decreased compared to BCP-LBL patients of all other pediatric ages (p < 0.0001).

Pediatric B-cell precursor (BCP) lymphoblastic malignancies are neoplasms with manifestation either in the bone marrow or blood (BCP acute lymphoblastic leukemia [BCP-ALL]) or are less common in extramedullary tissue (BCP lymphoblastic lymphoma [BCP-LBL]). Although both presentations are similar in morphology and immunophenotype, molecular studies have been virtually restricted to BCP-ALL so far. The lack of molecular studies on BCP-LBL is due to its rarity and restriction on small, mostly formalin-fixed paraffin-embedded (FFPE) tissues. Here, to our knowledge, we present the first comprehensive mutational and transcriptional analysis of what we consider the largest BCP-LBL cohort described to date (n = 97). Whole-exome sequencing indicated a mutational spectrum of BCP-LBL, strikingly similar to that found in BCP-ALL. However, epigenetic modifiers were more frequently mutated in BCP-LBL, whereas BCP-ALL was more frequently affected by mutation in genes involved in B-cell development. Integrating copy number alterations, somatic mutations, and gene expression by RNA sequencing revealed that virtually all molecular subtypes originally defined in BCP-ALL are present in BCP-LBL, with only 7% of lymphomas that were not assigned to a subtype. Similar to BCP-ALL, the most frequent subtypes of BCP-LBL were high hyperdiploidy and ETV6::RUNX1. Tyrosine kinase/cytokine receptor rearrangements were detected in 7% of BCP-LBL. These results indicate that genetic subtypes can be identified in BCP-LBL using next-generation sequencing, even in FFPE tissue, and may be relevant to guide treatment.

Twenty percent of children with T‐cell lymphoblastic lymphoma (T‐LBL) will relapse and have an extremely poor outcome. Currently, we can identify a genetically low‐risk subgroup in pediatric T‐LBL, yet these high‐risk patients who need intensified or alternative treatment options remain undetected. Therefore, there is an urgent need to recognize these high‐risk T‐LBL patients through identification of molecular characteristics and biomarkers. By using RNA sequencing which was performed in 29/49 T‐LBL patients who were diagnosed in the Princess Maxima Center for Pediatric Oncology between 2018 and 2023, we discovered a previously unknown high‐risk biological subgroup of children with T‐LBL. This subgroup is characterized by NOTCH1 gene fusions, found in 21% of our T‐LBL cohort (6/29). All patients presented with a large mediastinal mass, pleural/pericardial effusions, and absence of blasts in the bone marrow, blood, and central nervous system. Blood CCL17 (C‐C Motif Chemokine Ligand 17, TARC) levels were measured at diagnosis in 26/29 patients, and all six patients with NOTCH1 gene fusions patients exclusively expressed highly elevated blood CCL17 levels, defining a novel and previously not known clinically relevant biomarker for T‐cell lymphoblastic lymphoma. Four out of these six patients relapsed during therapy, a fifth developed a therapy‐related acute myeloid leukemia during maintenance therapy. These data indicate that T‐LBL patients with a NOTCH1 fusion have a high risk of relapse which can be easily identified using a blood CCL17 screening at diagnosis. Further molecular characterization through NOTCH1 gene fusion analysis offers these patients the opportunity for treatment intensification or new treatment strategies.

Twenty percent of children with T-cell lymphoblastic lymphoma (T-LBL) will relapse and have an extremely poor outcome. Currently, we can identify a genetically low-risk subgroup in pediatric T-LBL, yet these high-risk patients who need intensified or alternative treatment options remain undetected. Therefore, there is an urgent need to recognize these high-risk T-LBL patients through identification of molecular characteristics and biomarkers. By using RNA sequencing which was performed in 29/49 T-LBL patients who were diagnosed in the Princess Maxima Center for Pediatric Oncology between 2018-2023, we discovered a previously unknown high-risk biological subgroup of children with T-LBL. This subgroup is characterized by NOTCH1 gene fusions, found in 21% of our T-LBL cohort (6/29). All patients presented with a large mediastinal mass, pleural/pericardial effusions, and absence of blasts in the bone marrow, blood, and central nervous system. Blood CCL17 (C-C Motif Chemokine Ligand 17, TARC) levels were measured at diagnosis in 26/29 patients, and all six patients with NOTCH1 gene fusions patients exclusively expressed highly elevated blood CCL17 levels, defining a novel and previously not known clinically relevant biomarker for T-cell lymphoblastic lymphoma. Four out of these six patients relapsed during therapy, a fifth developed a therapy related acute myeloid leukemia during maintenance therapy. These data indicate that T-LBL patients with a NOTCH1 fusion have a high risk of relapse which can be easily identified using a blood CCL17 screening at diagnosis. Further molecular characterization through NOTCH1 gene fusion analysis offers these patients the opportunity for treatment intensification or new treatment strategies.