p53 mutation as the second event in juvenile chronic myelogenous leukemia in a patient with neurofibromatosis type 1

Neurofibromatosis Type 1 and tumorigenesis: molecular mechanisms and therapeutic implications

Neurofibromatosis Type 1 (NF1) is a common autosomal dominant disease characterized by complex and multicellular neurofibroma tumors, and less frequently by malignant peripheral nerve sheath tumors (MPNSTs) and optic nerve gliomas. Significant advances have been made in elucidating the cellular, genetic, and molecular biology involved in tumor formation in NF1. Neurofibromatosis Type 1 is caused by germline mutations of the NF1 tumor suppressor gene, which generally result in decreased intracellular neurofibromin protein levels, leading to increased cascade Ras signaling to its downstream effectors. Multiple key pathways are involved with the development of tumors in NF1, including Ras/mitogen-activated protein kinase (MAPK) and Akt/mammalian target of rapamycin (mTOR). Interestingly, recent studies demonstrate that multiple other developmental syndromes (in addition to NF1) share phenotypic features resulting from germline mutations in genes responsible for components of the Ras/MAPK pathway. In general, a somatic loss of the second NF1 allele, also referred to as loss of heterozygosity, in the progenitor cell, either the Schwann cell or its precursor, combined with haploinsufficiency in multiple supporting cells is required for tumor formation. Importantly, a complex series of interactions with these other cell types in neurofibroma tumorigenesis is mediated by abnormal expression of growth factors and their receptors and modification of gene expression, a key example of which is the process of recruitment and involvement of the NF1+/– heterozygous mast cell. In general, for malignant transformation to occur, there must be accumulation of additional mutations of multiple genes including INK4A/ARF and P53, with resulting abnormalities of their respective signal cascades. Further, abnormalities of the NF1 gene and molecular cascade described above have been implicated in the tumorigenesis of NF1 and some sporadically occurring gliomas, and thus, these treatment options may have wider applicability. Finally, increased knowledge of molecular and cellular mechanisms involved with NF1 tumorigenesis has led to multiple preclinical and clinical studies of targeted therapy, including the mTOR inhibitor rapamycin, which is demonstrating promising preclinical results for treatment of MPNSTs and gliomas.

Facial papules as a marker of internal malignancy

Facial papules (bumps) confront the general practitioner during every face-to-face meeting with the patient. Increased awareness and recognition of the facial papules that represent cutaneous signs of internal malignancy will allow an early, aggressive workup and treatment of any associated cancer. This article details the clinical presentation, etiology, pathologic findings, and associated malignancy for such presentations. A skin biopsy for histopathologic diagnosis is necessary to distinguish these clues to underlying malignancy from the numerous benign lesions that cause facial papules.

Germline and somatic NF1 gene mutation spectrum in NF1-associated malignant peripheral nerve sheath tumors (MPNSTs)

About 10% of neurofibromatosis type 1 (NF1) patients develop malignant peripheral nerve sheath tumors (MPNSTs) and represent considerable patient morbidity and mortality. Elucidation of the genetic mechanisms by which inherited and acquired NF1 disease gene variants lead to MPNST development is important. A study was undertaken to identify the constitutional and somatic NF1 mutations in 34 MPNSTs from 27 NF1 patients. The NF1 germline mutations identified in 22 lymphocytes DNA from these patients included seven novel mutations and a large 1.4-Mb deletion. The NF1 germline mutation spectrum was similar to that previously identified in adult NF1 patients without MPNST. Somatic NF1 mutations were identified in tumor DNA from 31 out of 34 MPNSTs, of which 28 were large genomic deletions. The high prevalence (>90%) of such deletions in MPNST contrast with the =or<20% found in benign neurofibromas and is indicative of the involvement of different mutational mechanisms in these tumors. Coinactivation of the TP53 gene by deletion, or by point mutation along with NF1 gene inactivation, is known to exacerbate disease symptoms in NF1, therefore TP53 gene inactivation was screened. DNA from 20 tumors showed evidence for loss of heterozygosity (LOH) across the TP53 region in 11 samples, with novel TP53 point mutations in four tumors.

Molecular, genetic, and cellular pathogenesis of neurofibromas and surgical implications

Neurofibromatosis 1 (NF1) is a common autosomal dominant disease characterized by complex and multicellular neurofibroma tumors. Significant advances have been made in the research of the cellular, genetic, and molecular biology of NF1. The NF1 gene was identified by positional cloning. The functions of its protein product, neurofibromin, in RAS signaling and in other signal transduction pathways are being elucidated, and the important roles of loss of heterozygosity and haploinsufficiency in tumorigenesis are better understood. The Schwann cell was discovered to be the cell of origin for neurofibromas, but understanding of a more complicated interplay of multiple cell types in tumorigenesis, specifically recruited heterogeneous cell types such as mast cells and fibroblasts, has important implications for surgical therapy of these tumors. This review summarizes the most recent NF1 and neurofibroma literature describing the pathogenesis and treatment of nerve sheath tumors. Understanding the biological underpinnings of tumorigenesis in NF1 has implications for future surgical and medical management of neurofibromas.

Molecular genetic analyses in neurofibromatosis type 1 patients with tumors

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders. NF1 is clinically characterized by neurofibromas, pigmentation anomalies, and an increased risk of malignant tumors. The NF1 gene product, neurofibromin, has a GTPase-activating protein domain (GRD) that interacts with the Ras protein, which is crucial in regulating signal transduction and cell proliferation/differentiation. We performed mutation analyses in the NF1-GRD region (exons 21-27a) and in exons 4b, 16, 29, and 37, and intron 28 in 17 NF1 patients with tumors. We identified a large deletion in the NF1 gene in a patient with a rhabdomyosarcoma as well as a variation in intron 22 in a patient with an optic glioma. We also found a 4-base pair deletion in another patient with optic glioma. In addition, allelic loss of the NF1 locus was shown in a pilocytic astrocytoma. Functional analyses of mutations in the NF1 gene may provide further insights into the pathogenesis of NF1 tumors.

A case of neurofibromatosis and breast cancer: loss of heterozygosity of NF1 in breast cancer

Only a few cases with breast cancer and neurofibromatosis type 1 (NF1) have been reported in the literature. Here, we present a family with a history of neurofibromatosis and breast cancer. No hereditary NF1 mutation was observed in this case. Loss of heterozygosity (LOH) analyses of the breast tumor revealed LOH in the NF1 region. In this family, the proband and her mother had breast cancer. The proband was diagnosed with breast cancer at the age of 23 years. No BRCA1 or BRCA2 mutations were observed in the proband's peripheral blood DNA nor were such mutations observed in the immunohistochemically analyzed paraffin block of the tumor DNA. Neurofibromin, encoded by the NF1 gene region, was reported as nearly absent in human breast cancer-MDA-MP-231 cells. Neurofibromin is similar in function to the GTPase activating protein (GAP), p120 GAP. It also accelerates the inactivation of the RAS oncogene. Molecular alterations in NF1 gene region cause neurofibromatosis. LOH in the tumor tissue of our case supports the role of the NF1 gene in the etiology of some cases of breast cancer.

Characterization of the somatic mutational spectrum of the neurofibromatosis type 1 (NF1) gene in neurofibromatosis patients with benign and malignant tumors

One of the main features of neurofibromatosis type 1 (NF1) is benign neurofibromas, 10-20% of which become transformed into malignant peripheral nerve sheath tumors (MPNSTs). The molecular basis of NF1 tumorigenesis is, however, still unclear. Ninety-one tumors from 31 NF1 patients were screened for gross changes in the NF1 gene using microsatellite/restriction fragment length polymorphism (RFLP) markers; loss of heterozygosity (LOH) was found in 17 out of 91 (19%) tumors (including two out of seven MPNSTs). Denaturing high performance liquid chromatography (DHPLC) was then used to screen 43 LOH-negative and 10 LOH-positive tumors for NF1 microlesions at both RNA and DNA levels. Thirteen germline and 12 somatic mutations were identified, of which three germline (IVS7-2A>G, 3731delT, 6117delG) and eight somatic (1888delG, 4374-4375delCC, R2129S, 2088delG, 2341del18, IVS27b-5C>T, 4083insT, Q519P) were novel. A mosaic mutation (R2429X) was also identified in a neurofibroma by DHPLC analysis and cloning/sequencing. The observed somatic and germline mutational spectra were similar in terms of mutation type, relative frequency of occurrence, and putative underlying mechanisms of mutagenesis. Tumors lacking mutations were screened for NF1 gene promoter hypermethylation but none were found. Microsatellite instability (MSI) analysis revealed MSI in five out of 11 MPNSTs as compared to none out of 70 neurofibromas (p=1.8 x 10(-5)). The screening of seven MPNSTs for subtle mutations in the CDKN2A and TP53 genes proved negative, although the screening of 11 MPNSTs detected LOH involving either the TP53 or the CDKN2A gene in a total of four tumors. These findings are consistent with the view that NF1 tumorigenesis is a complex multistep process involving a variety of different types of genetic defect at multiple loci.

Malignancy: Tumor Suppressor Gene Aberrations in Acute Myelogenous Leukemia

Acute myelogenous leukemia is a heterogeneous disease that appears to evade the normal regulatory controls of tumor suppressor genes. Studies in AML have documented mutations in both p53 and Retinoblastoma (Rb) genes, but these mutations are relatively uncommon, especially compared to their mutational frequency in solid tumors. In addition, expression abnormalities have now been documented in several tumor suppressor genes or related genes including MDM2, p73, Rb, p14(ARF), p15(INK4B), and p16(INK4A). We review the current literature regarding tumor suppressor genes in AML and suggest how these genes may be involved in the development of the disease.