José Luis Fuster

Background: Methotrexate-induced neurotoxicity (MTX-NTX) is a severe complication during childhood acute lymphoblastic leukemia (ALL) treatment, yet its underlying pharmacogenetic determinants remain incompletely understood. Methods: A multicenter retrospective nationwide case–control study was performed including 71 pediatric ALL patients (34 MTX-NTX cases and 37 controls). Targeted next-generation sequencing of 17 genes involved in MTX transport, intracellular metabolism and folate pathways was performed. Results: Transport-related genes accounted for 61.4% of all detected variants and showed the highest number of nominally significant variants. Pathway-level burden analysis demonstrated a significant enrichment of transporter-related variants in patients with MTX-NTX compared with controls (FDR-adjusted p = 0.004), whereas the analysis for folate/metabolism-related genes did not remain significant after multiple-testing (FDR-adjusted p = 0.096). Similar findings were observed in the stroke-like syndrome (SLS) subgroup (FDR-adjusted p = 0.014 and 0.108, respectively). Gene-level burden analysis identified ABCG2 and ABCC4 as the predominant contributors, harboring both 18.4% of significant variants in the overall MTX-NTX analysis and 20.6% and 17.6%, respectively in the SLS phenotype. Moreover, the distribution of significant variants was strongly correlated between the overall MTX-NTX and SLS analyses (Spearman’s ρ = 0.549, p = 0.022). Volcano plot analysis revealed ABCG2 as the gene showing the most prominent pattern of nominal associations, containing both the variants associated with a protective direction (e.g., c.1728-46G>A, p = 2.6 × 10⁻⁴) and variants associated with increased risk, including c.34G>A and c.203+36A>G (p = 0.002) and c.263+10A>G (p = 0.0097). Phenotype-specific analyses revealed distinct genetic signatures across neurological manifestations, with transporter genes predominating in focal neurological deficits. Conclusions: Our findings suggest that genetic variability in ABC transporter genes may contribute to susceptibility to MTX-NTX, whereas folate metabolism genes may represent complementary phenotype-modifying factors. These findings are exploratory and require validation in larger, independent cohorts and functional studies.

Background: Methotrexate-induced neurotoxicity (MTX-NTX) is a severe complication during childhood acute lymphoblastic leukemia (ALL) treatment, yet its underlying pharmacogenetic determinants remain incompletely understood. Methods: A multicenter retrospective nationwide case-control study was performed including 71 pediatric ALL patients (34 MTX-NTX cases and 37 controls). Targeted next-generation sequencing of 17 genes involved in MTX transport, intracellular metabolism and folate pathways was performed. Results: Transport-related genes accounted for 61.4% of all detected variants and showed the highest overall variant burden. Pathway-level burden analysis demonstrated a significant enrichment of transporter-related variants in patients with MTX-NTX compared with controls (FDR-p = 0.004), whereas the analysis for folate/metabolism-related genes did not remain significant after multiple-testing (FDR-p = 0.096). Similar findings were observed in the stroke-like syndrome (SLS) subgroup (FDR-p = 0.014 and 0.108, respectively). Gene-level burden analysis identified ABCC4 as the predominant contributor, harboring 20.0% of significant variants in the overall MTX-NTX analysis and 22.8% in the SLS phenotype, followed by ABCC1 and MTHFR. Moreover, the distribution of significant variants was strongly correlated between the overall MTX-NTX and SLS analyses (Spearman’s ρ = 0.616, p = 0.011). Volcano plot analysis revealed ABCG2 as the main susceptibility locus, containing both the variants with the strongest protective associations (e.g., c.1728-46G>A, p = 2.6×10⁻⁵) and the highest-risk variants, including c.34G > A and c.203+36A > G (p = 0.002) and c.263+10A > G (p = 0.009). Phenotype-specific analyses revealed distinct genetic signatures across neurological manifestations, with transporter genes predominating in focal neurological deficits. Conclusion: Our findings suggest that genetic variability in ABC transporter genes may contribute substantially to susceptibility to MTX-NTX, whereas folate metabolism genes would act as complementary phenotype-modifiers factors.

KMT2A-rearranged B-cell acute lymphoblastic leukemia (KMT2A-r B-ALL) is an aggressive subtype of leukemia, characterized by high relapse rates, therapy resistance, and poor prognosis. Although CD19-targeted immunotherapies have significantly benefited patients with relapsed/refractory (R/R) disease, relapses remain common and long-term survival is especially poor in KMT2A-r B-ALL patients. We recently identified the membrane-bound proteoglycan NG2 (CSPG4) as direct transcriptional target of KMT2A fusions, with its expression associated with poor prognosis, early relapse, and glucocorticoid resistance in KMT2A-r B-ALL. However, the molecular mechanism underlying the aggressiveness of KMT2A-r B-ALL remains poorly understood. Here, we identify the α4 integrin subunit (ITGA4) and NG2 as a key biological axis contributing to leukemic aggressiveness. NG2 expression promotes proliferation and migration of KMT2A-r B-ALL cells and it is associated with Rho GTPase activity in an ITGA4-dependent manner. In vivo studies using immunodeficient mice demonstrated that ITGA4 and NG2 cooperate to promote leukemia progression as combined genetic ablation of both genes significantly delayed disease onset and prolonged survival. Notably, Natalizumab (NTZ) - an FDA/EMA-approved monoclonal antibody targeting ITGA4 - delayed leukemia progression and potentiated the efficacy of standard-of-care chemotherapy in KMT2A-r B-ALL patient-derived xenograft (PDX) models. Collectively, our findings define a novel ITGA4-NG2 signaling axis that drives the aggressiveness of KMT2A-r B-ALL and support the repurpose of NTZ as an adjuvant therapeutic strategy for this high-risk leukemia subtype.

Third allogeneic hematopoietic stem cell transplantation (HSCT3) is rarely performed in pediatric patients and is associated with high toxicity and mortality. Data on outcomes in this setting remain scarce. We conducted a retrospective multicenter study within the Spanish GETH‐TC Pediatric group including 29 children and adolescents who underwent HSCT3 between 2011 and 2024 for malignant ( n = 21) or nonmalignant ( n = 8) diseases. Patient‐, disease‐, and transplant‐related variables were analyzed, and survival outcomes were estimated using Kaplan–Meier methods. Engraftment was achieved in 22 patients (75.8%). Grade III–IV acute GvHD occurred in 7% and chronic GvHD in 11%. Severe viral infections were frequent (48%), as were bacterial (34%) and fungal infections (21%). By day +100, TRM was 31%, and overall mortality at last follow‐up was 66%, predominantly transplant‐related. Estimated 12‐month overall survival (OS) and event‐free survival (EFS) were 39.5% and 32.7%, respectively. Outcomes differed by indication: patients with malignant diseases had limited survival, particularly when transplanted with measurable residual disease, whereas outcomes were more favorable in nonmalignant disorders, with a 12‐month EFS of 50%. Survival was also associated with preserved performance status. HSCT3 in children remains a high‐risk procedure. Meaningful survival is restricted to carefully selected patients and appears more achievable in nonmalignant indications.

Diamond-Blackfan anemia syndrome (DBAS) is marked by defective erythropoiesis caused by impaired ribosome biogenesis and aberrant signaling. Here, we investigate how ribosomal stress-induced activation of the NLRP1 inflammasome affects erythroid differentiation in DBAS. We demonstrate that FDA/EMA-approved tyrosine kinase inhibitors (TKIs) effectively mitigate defective erythropoiesis by inhibiting NLRP1 inflammasome activation. In K562 cells, nilotinib suppresses the ZAKα/P38/NLRP1/CASP1 axis, leading to increased GATA1 levels and upregulation of key erythroid genes. These effects were validated in human CD34⁺ hematopoietic stem and progenitor cells (HSPCs) and zebrafish models, where nilotinib, imatinib, and dasatinib promoted erythropoiesis while reducing caspase-1 activity. In Rps19-deficient zebrafish, RPS19-deficient human HSPCs, and HSPCs from DBAS patients, TKIs rescued erythroid differentiation and restored hemoglobin levels. Our findings highlight that targeting the NLRP1 inflammasome with TKIs may provide a novel therapeutic strategy for DBAS and other ribosomopathies.

Background: Survival among children and adolescents and young adults (AYA) with cancer has improved substantially over recent decades; however, dominant survivorship models remain reactive—activated post-treatment and anchored to static exposure- and organ-based screening. This design underuses the anticipatory window at diagnosis and overlooks environmental and social determinants that modulate outcomes across the life course. Methods: We narratively reviewed international frameworks including the Children’s Oncology Group (COG), the International Late Effects of Childhood Cancer Guideline Harmonization Group (IGHG), the Pan-European Network for Care of Survivors after Childhood and Adolescent Cancer (PanCare) and the National Comprehensive Cancer Network (NCCN), and synthesized evidence on environmental determinants, exposomics, toxicogenomics, and implementation. Building on two decades of real-world practice, we describe the evolution from the Pediatric Environmental History (PEHis) to the Ambiomic Health Compass (AHC), integrating genomic, exposomic, geospatial, clinical, and biomonitoring layers into routine care. In this framework, survivorship is conceptualized as beginning at the time of cancer diagnosis (“day 0”). Results: PEHis operationalizes guideline-based care with structured environmental and social assessment, personalized plans, and community integration, contributing to improved survival, healthier behaviors, reduced treatment-related mortality and stronger oncology–primary-care coordination. AHC extends PEHis with dynamic risk recalibration, contextual alerts, targeted biomonitoring, and toxicogenomic interpretation, enabling anticipatory decisions from day 0. The manuscript summarizes the paradigm shift (current vs. Ambiomic models), the domain-specific expansion over existing guidelines, the core clinical/system tools, and time-bound metrics (12, 24, 60 months) to support implementation and evaluation. Conclusions: Survivorship should move upstream—from late surveillance to ambiomic, exposure-aware care beginning at diagnosis. Integrating advanced exposomics, mutational epidemiology, and explainable analytics can reduce preventable events and chronicity, enhance equity, and align pediatric oncology with planetary health. The PEHis–AHC continuum offers a scalable blueprint for next-generation survivorship programs in Europe and beyond. Ambiomic medicine does not replace precision medicine—it completes and extends it by integrating exposomics, social context, and anticipatory analytics from day 0.

Background. Survival after childhood and adolescent and young adult (AYA) cancer has improved substantially; however, dominant survivorship models remain reac-tive—activated post-treatment and anchored to static, exposure- and organ-based screening. This design underuses the anticipatory window at diagnosis and overlooks environmental and social determinants that modulate outcomes across the life course. Methods. We narratively reviewed international frameworks (COG, IGHG, PanCare, NCCN) and synthesized evidence on environmental determinants, exposomics, toxi-cogenomics, and implementation. Building on two decades of real-world practice, we describe the evolution from the Pediatric Environmental History (PEHis) to the Ambiomic Health Compass (AHC), integrating genomic, exposomic, geospatial, clinical, and bio-monitoring layers into routine care. In this framework, survivorship is conceptualized as beginning at the time of cancer diagnosis (“day 0”). Results. PEHis operationalizes guideline-based care with structured environmental and social assessment, personalized plans, and community integration, contributing to improved survival, healthier be-haviors, reduced treatment-related mortality and stronger oncology–primary-care coor-dination. AHC extends PEHis with dynamic risk recalibration, contextual alerts, targeted biomonitoring, and toxicogenomic interpretation, enabling anticipatory decisions from day 0. The manuscript summarizes the paradigm shift (current vs. Ambiomic models), the domain-specific expansion over existing guidelines, the core clinical/system tools, and time-bound metrics (12, 24, 60 months) to support implementation and evaluation. Conclusions. Survivorship should move upstream—from late surveillance to ambiomic, exposure-aware care beginning at diagnosis. Integrating advanced exposomics, muta-tional epidemiology, and explainable analytics can reduce preventable events and chronicity, enhance equity, and align pediatric oncology with planetary health. The PEHis–AHC continuum offers a scalable blueprint for next-generation survivorship programs in Europe and beyond. Ambiomic medicine does not replace precision medi-cine—it completes and extends it by integrating exposomics, social context, and antici-patory analytics from day 0.

Background/Objectives: Intrachromosomal amplification of chromosome 21 (iAMP21) represents a rare and heterogeneous distinct cytogenetic subgroup of B-cell precursor acute lymphoblastic leukemia (ALL) initially associated with a poor prognosis. Treatment intensification with additional doses of methotrexate and asparaginase was associated with better treatment outcomes. Methods: In this retrospective single-center study, we evaluated the impact of iAMP21 on treatment outcome in a cohort of pediatric patients treated with an intensified asparaginase regimen and describe the genomic landscape of four patients with iAMP21. Results: Four out of 89 patients > 1 year old were classified as iAMP21 positive. Five-year event-free survival (EFS) was inferior in the iAMP21-positive group: 25% versus 85.6% (p = 0.001). The cumulative incidence of relapse and treatment-related mortality were 50% vs. 9.9% and 0% vs. 2.38%, respectively, in the iAMP21-positive and non-iAMP21 groups (p = 0.02 and 0.76, respectively). These results did not translate into a significant difference in overall survival: 100% vs. 93.7% (p = 0.6). The presence of iAMP21 (HR 7.68, 95% CI 2.04–29.05; p = 0.002) and a measurable residual disease ≥1% after induction on day +33 (HR 8.82, 95% CI 2.6–29.91; p = 0.001) retained significant negative impact on EFS in multivariate analysis. Conclusions: We found an independent significant prognostic impact of iAMP21 on EFS among pediatric patients with ALL, and clinical presentation and early treatment response did not classify these patients as HR. Diverse genetic backgrounds among iAMP21-positive patients might influence the treatment response and outcome of this heterogeneous disease.