With increasing survival in acute lymphoblastic leukemia (ALL), long-term toxicities have become a critical aspect. A novel measure, designated Severe Toxicity-free survival (STFS), was developed through international consensus to integrate the most severe, symptomatic organ toxicities in outcome evaluation. This measure has not been applied to real-world data before. We assessed the incidence of 21 predefined Severe Toxicities in a nationwide cohort of 506 ALL patients aged 1-45 years treated according to the NOPHO ALL2008 protocol. At five years, event-free survival was 84.4% (95% CI: 81.3-87.7%) and Severe Toxicity-event-free survival was 78.4% (95% CI: 74.9-82.1%), with significantly lower values in adults (aged 18-45 years) than children (61.6% [52.6-72.2%] vs 82.4% [78.8-86.2%]; log-rank p < 0.001). The most common Severe Toxicities were severe osteonecrosis limiting activities of daily function (N = 20) and disabling paralytic and neuropathic conditions (N = 16). Exploratory analyses showed that 10-17-year-olds had the highest risk of Severe Toxicities similar to that of adults. These findings highlight a burden of severe, long-term toxicities in ALL survivors overlooked by traditional outcome measures, also following frontline therapy only. STFS should be incorporated in future trials for meaningful outcome evaluation and international comparisons across treatment strategies.

The inclusion of nine myelodysplasia-related gene (MRG) mutations (ASXL1, BCOR, EZH2, RUNX1, SF3B1, SRSF2, STAG2, U2AF1, ZRSR2) as adverse risk factors in the ELN risk classification has reshaped classification in acute myeloid leukemia (AML). AML with FLT3-ITD mutations and co-occurring MRG alterations is now classified to the ELN adverse risk group although supporting evidence remains limited. Among 4,078 patients with AML with available molecular information included in the HARMONY platform, 862 harbored FLT3-ITD mutations and underwent intensive chemotherapy. Of these, 171 (20%) exhibited co-occurring MRG mutations at diagnosis. In this cohort, MRGs were not independently associated with relapse-free survival (RFS) or overall survival (OS). In the FLT3-ITD/NPM1 co-mutated subgroup, MRG mutations were rare (9%) and showed no prognostic impact. Conversely, in FLT3-ITD/NPM1 wildtype AML, MRG mutations were predictive of shorter RFS (HR 1.37, 95%CI 1.01 - 1.88, p = 0.046) and OS (HR 1.34, 95%CI 1.02-1.74, p = 0.032) in multivariable analysis with survival times comparable to the ELN adverse risk category. The allelic ratio of FLT3-ITD did not further stratify OS and RFS in this subgroup. These findings suggest that the prognostic relevance of MRG mutations in FLT3-ITD AML is modulated by NPM1 co-mutational status and mirror findings in AML lacking FLT3-ITD.

Hypoxia-inducible factors (HIFs) are master transcriptional regulators, central to cellular survival in hypoxia and frequently activated within malignancy. Whilst malignant context directs the role of HIFs within oncogenesis, these mechanisms are not well characterised. Applying the JAK2V617F myeloproliferative neoplasms (MPNs) oncogene-driver model, in which HIF-1α is stabilised in normoxia (20% O2), we sought to determine whether the modality of HIF-1 activation directs its function. Through direct analysis of hypoxia-activated vs. JAK2V617F-activated HIF-1 at the chromatin, we define a JAK2V617F-HIF-1 regulon that diverges from canonical HIF/hypoxia targets. In a cohort of 172 JAK2V617F-MPN patients, we observe significant association of the JAK2V617F-HIF-1 regulon, but not canonical HIF-1 gene signatures, with disease severity, progression, and patient survival. We further define a subset gene signature (HIF1-MPN-BP) significantly associated with spontaneous transformation to blast phase MPNs. Finally, we identify that JAK2V617F-induced HIF-1α stabilisation is mediated via PIM1 kinase. Our findings demonstrate that HIF-1 activation by the JAK2V617F-PIM1 axis significantly alters HIF-1 transcription function, desensitising HIF-1 activity to cellular oxygen levels, and restricting the HIF-1 regulon to a set of disease-associated target genes within JAK2V617F-MPNs. These findings restore the potential for specific therapeutic targeting of HIF-1 by delineating malignant activation from the physiological hypoxic response.