Background: In recent years, oncogenic understanding of T-ALL has led to the identification of multiple molecular markers. However, each molecular abnormality accounts for a small proportion of cases and risk stratification at diagnosis still relies on age, clinical presentation, and early response to therapy. NOTCH1 and/or FBXW7 mutations have been recently reported to be a recurrent abnormality in T-ALL, both leading to activation of the NOTCH pathway. Studies in pediatric series have suggested a favorable outcome for NOTCH1 mutated T-ALL, but this has not been evaluated in large series of adult cases. Furthermore, FBXW7 prognostic impact remains unknown in both populations.

Methods: In order to evaluate the incidence of these mutations and their prognostic impact in adults, we performed a retrospective analysis of 141 patients (median age, 28 years) with T-ALL treated within the LALA-94 (N=87) or the more recent GRAALL-2003 (N=54) French trials. These patients were representative of the overall population since their outcome did not differ from the overall T-ALL cases treated in either LALA-94 (estimated 3-year OS, 41%) or GRAALL-2003 (estimated 3-year OS, 66%) trial. Furthermore, the patients from the LALA-94 and the GRAALL-2003 trials did not differ with respect to sex ratio, age, WBC, and initial complete remission rate (92% and 98%, respectively). Exons 26 (HD N-terminal), 27 (HD C-terminal), 28 (juxtamembrane domain) and 34 (transactivation domain TAD and the PEST domain) of NOTCH1 and exons 9, 10 and 12 of WD40 domain of FBXW7 were sequenced.

Results: We identified 101 cases with NOTCH1 and/or FBXW7 mutations (72%) and 40 wild type (WT) samples (28%). NOTCH1 was mutated in 88 patients (59 HD only, 15 HD+PEST, 9 PEST only, 5 other). FBXW7 was mutated in 34 patients, alone in 13 cases or in association with NOTCH1 mutations in 21 cases. There was no significant correlation between NOTCH1 and/or FBXW7 mutations and immunophenotypic or oncogenetic features. There was a trend for a higher WBC and more frequent CNS involvement in patients demonstrating WT NOTCH1 and FBXW7. Similarly, high-risk MRC/ECOG criteria (age>35y and/or WBC>100G/L) were found in 56% of patients from the mutated subgroup versus 73% in the WT subgroup (P=0.06). The prognostic impact of NOTCH1 mutations alone did not reach statistical significance on multivariate analysis (P=0.09). On the other hand, multivariate analysis showed that the GRAALL-2003 trial and the presence of NOTCH1 and/or FBXW7 mutations were the only factors associated with a longer EFS (P=0.001 and 0.035, respectively). Median EFS was 36 months for patients with NOTCH1 and/or FBXW7 mutations versus 17 months for WT patients.

Conclusions: These data demonstrate that NOTCH pathway activation by either NOTCH1 or FBXW7 mutation identifies a large group of T-ALL adult patients (72%) with a favorable outcome that could be used for treatment stratification.

Disclosures: No relevant conflicts of interest to declare.

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