Manon Delafoy & al, HemaSphere, 2025

T-cell acute lymphoblastic leukemia (T-ALL) is a rare and aggressive hematological malignancy primarily affecting adolescents and young adults and is scarce in infants and toddlers under age 3.

Unlike B-ALL, T-ALL in this young population remains poorly characterized due to limited data and lacks evidence-based guidelines to help clinicians determine the optimal treatment approach.

In this study, we conducted a comprehensive genetic analysis of infant/toddler T-ALL cases from a French national cohort, utilizing high-throughput targeted sequencing, optical genome mapping, and RNA sequencing.

Genetic analysis revealed the absence of TLX1/3 dysregulation. Instead, we identified a significant prevalence of NKX2 rearrangements (n = 9, 33%), co-occurring with MYB alterations (n = 5/9) or chromothripsis-like events (n = 3/9). Additional findings included TAL1/-like anomalies (30%), STAG2::LMO2 (15%), ETS rearrangements (15%), and rarely, KMT2A rearrangements (7%).

Comparative analyses with 245 patients aged 3–18 years, enrolled in the pediatric FRALLE2000T French protocol, underscored the distinct clinical and genetic profiles of infants/toddlers.

Despite presenting with higher rates of hyperleukocytosis and slower responses to treatment, they demonstrated comparable survival outcomes to older pediatric patients, with a 5-year overall survival (OS) rate of 75.4% (95% confidence interval [CI]: 60.0%–94.8%) versus 75.2% (95% CI: 69.8%–81.1%), p = 0.86. Notably, alterations in NKX2, KMT2A, and STAG2::LMO2 delineated oncogenic subgroups exhibiting a remarkable 100% OS rate, while patients with TAL1 or ETS dysregulation experienced less favorable outcomes.

This was further supported by analyses of data from the COG AALL0434 trial, enhancing our understanding of T-ALL in infants/toddlers. Large-scale collaborative studies remain essential to confirm these findings and refine treatment strategies.

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