Background: Children with neurofibromatosis type 1 (NF1) are at increased risk of developing benign and malignant solid tumors as well as hematologic malignancies, including de novo juvenile chronic myelogenous leukemia, monosomy 7 syndrome, and acute myelogenous leukemia. The normal NF1 allele is frequently deleted in the bone marrow cells from NF1 patients with hematologic malignancies, suggesting a pathogenic role in primary leukemogenesis. The authors report monosomy 7 myelodysplastic syndrome (MDS) as a second malignant neoplasm (SMN) in five children with sporadic NF1, the results of molecular analysis for NF1 and ras alterations in their bone marrow, and summarize their experience with SMNs in pediatric patients with NF1.
Methods: Monosomy 7 MDS was diagnosed as an SMN in five children with NF1 by morphologic and cytogenetic studies of bone marrow specimens. DNA extracted from these malignant bone marrows was analyzed for allelic loss at the NF1 locus and for the presence of ras mutations. The Children's Hospital of Philadelphia (CHOP) Tumor Registry was also reviewed to estimate the incidence of SMNs in pediatric NF1 patients.
Results: Bone marrow specimens from four patients retained constitutional heterozygosity at the NF1 locus; one specimen was uninformative. There was no evidence of activating ras mutations. The risk of an SMN was approximately 11% among the 64 NF1 registrants with primary malignancies in the CHOP registry, but was 75% (6 of 8) among patients treated for a pediatric embryonal cancer.
Conclusions: Children with NF1 are susceptible to the development of malignant myeloid disorders both as a primary event and as an SMN. Additional molecular genetic analysis is necessary to determine if the NF1 gene is inactivated by somatic mutation in these secondary leukemias.