Discussion
Neurofibromatosis type I caused by NF1 mutations is classified as an RAS disease (RASopathy)3, with unique phenotypic characteristics, such as CALM, skin neurofibroma, bone dysplasia and Lisch nodules of the iris. Patients have a high risk of benign and malignant tumors4, with an estimated 59.6% lifetime cancer risk and a low long-term survival rate5. A follow-up study of 2,427 patients with neurofibromatosis type I revealed that 9 (0.6%) patients had comorbid ALL, 2 had AML, 2 had chronic myeloid leukemia, and one had chronic lymphocytic leukemia6. A study including 1,021 adult patients with newly developed AML revealed that 5% of patients had NF1 mutations, and one-third of the gene mutation loci were located at threonine 676 (p.Thr676fs*24). This locus is associated with a lower CR rate and shorter OS7. RAS pathway mutations occur in more than 40% of pediatric ALL patients,8 but the proportion of NF1 mutations is minimal, and no relevant large-scale study findings are available.
The NF1 gene is located at chromosome 17q11.2, which spans 350 kb, including 57 constitution exons and 4 alternative spliced exons (9a, 10a2, 23a, and 48a), and encodes neurofibromin. Neurofibromin is a RAS-GTP-activating protein that inactivates RAS-GTP by accelerating its hydrolysis to RAS-GDP. Loss of NF1 gene expression may cause abnormal activation of RAS and downstream signaling pathways, mainly the RAF-MEK-ERK pathway. However, this gene also interacts with the PI3K-AKT-mTOR pathway to influence the secondary regulation of cell proliferation, differentiation, migration and apoptosis9 and increases the genetic susceptibility to benign and malignant tumors. In addition, it has been reported thatNF1 splicing site variation may trigger exon skipping, which in turn may affect the structure and function of proteins10. The vast majority of NF1 mutations are intragenic, including point mutations (85% -90%) and single or multiple exon deletions or duplications (2%). Fewer than 10% of deletions involve the entire gene and flanking genomic regions11. There is a strong genotype‒phenotype correlation with 17q11.2 microdeletion syndrome12. Detecting these mutations is dependent on multiplex ligation-dependent probe amplification (MLPA)13. Specific mutation types were not distinguished in this study. Thus, further research and improvements are needed.
This study revealed that NF1 mutations do not affect the overall effect of treatment on pediatric acute leukemia patients. Survival outcomes are associated with adverse cytogenetic features, risk assessment, treatment protocols, and disease progression. Patients with germline NF1 gene mutations had a poorer prognosis than those with somatic mutations, especially children with AML. However, all three children with AML in this study had a high risk and concurrent adverse genetic variants, such as KMT2A-MLLT3, MLL-AF9, andNUP98-HoxA9 . These patients had a poor remission rate after induction therapy. Moreover, only a small number of patients were included in this study. Therefore, the associations with prognosis should be further investigated. ALL patients mainly had intermediate risk, whereas AML patients mostly had high risk. Stratified therapy based on MRD guidance has been adopted, and targeted drugs such as blinatumomab, venetoclax and gilteritinib have been administered simultaneously. Both the low 5-year survival rate and high recurrence rate of AML are bottlenecks in the treatment of acute leukemia. High-risk children should actively undergo transplantation or use targeted drugs and new treatment protocols. In terms of fusion genes, some ALL patients carried a ZNF384 fusion gene rearrangement, which has not been reported previously. The transcription factor zinc finger protein 384 gene is located at chromosome 12q13 and can fuse with a variety of upstream partner genes, causing defects in the integrin signaling pathway. This fusion gene is associated with premature migration of bone marrow hematopoietic stem cells into the peripheral blood and may be one of the mechanisms of ALL.
In this study, the clinical manifestations of neurofibromatosis included CALM, freckles, xanthogranuloma, scoliosis, and benign intracranial lesions. No other benign or malignant tumors were discovered. Neurofibromatosis was more common in patients with germline NF1 gene mutations, which is consistent with the findings of previous studies14,15. Somatic NF1 gene mutations were mostly acquired cytogenetic mutations secondary to leukemic tumor cells. However, the possibility of chimeric mutations should be considered when patients present with clinical symptoms of neurofibromatosis. The clinical symptoms of neurofibromatosis are atypical, variable and appear gradually over time because of incomplete penetrance of the NF1 gene in children and adolescents. When germline NF1 gene mutations are identified or the patient exhibits relevant clinical symptoms, the French Neurofibromatosis Type I Guidelines 2020 should be followed for clinical follow-up16.
In the CNS, bright signals in the cerebellum, brainstem, thalamus and basal ganglia occur in 70% of children with neurofibromatosis; these signals indicate benign brain lesions that appear at approximately 3 years of age and gradually disappear between 20 and 30 years of age17. In this study, abnormal head nuclear magnetic resonance signals were observed in all three neurofibromatosis patients at the first visit, and these signals were slightly reduced during chemotherapy. Patient ALL-3 had more abnormal signals after drug withdrawal than before withdrawal. These lesions do not affect brain function or intellectual development. Optic pathway gliomas (OPGs) are the most common CNS tumors in children under 7 years of age withNF1 mutations, with an incidence of 15–20%. However, these patients are mostly asymptomatic,18 and no OPGs were found in this study.
Patients with neurofibromatosis mainly receive symptomatic treatment. The MEK inhibitor selumetinib is approved by the US Food and Drug Administration for the treatment of children with NF1 -associated plexiform neurofibromas. Interestingly, some studies have shown that the TKI inhibitors imatinib and nilotinib may decrease the volume of plexiform neurofibromas19,20. These two drugs are also used in Philadelphia chromosome-positive ALL patients, suggesting that the potential value of targeted drugs deserves further investigation in these patients.
In conclusion, this study is a single-center retrospective study with the largest number of children with NF1 mutation-positive acute leukemia available in China. However, most children have not stopped drug treatment. Further follow-up studies are needed to determine the long-term prognosis of these patients.
Conflict of Interest statement: The manuscript has no conflicts of interest.
Acknowledgements: Thank all the leukemia patients and their parents who provided cases, and thank all the medical staff who worked hard for it.
Ethics statement: We have affirm that informed consent of the case patients has been properly documented.
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Table 1 Clinical characteristics of patients with NF1 mutation-positive acute leukemia