Molecular and cytogenetic analysis of tumors in von Recklinghausen neurofibromatosis

Establishment and characterization of a recurrent malignant peripheral nerve sheath tumor cell line: RsNF

Malignant peripheral nerve sheath tumor (MPNST) is a highly aggressive and recurrent soft tissue sarcoma. It most commonly occurs secondary to neurofibromatosis type I, and it has a 5-year survival rate of only 8-13%. To better study the tumor heterogeneity of MPNST and to develop diverse treatment options, more tumor-derived cell lines are needed to obtain richer biological information. Here, we established a primary cell line of relapsed MPNST RsNF cells derived from a patient diagnosed with NF1 and detected the presence of NF1 mutations and SUZ12 somatic mutations through whole-exome sequencing(WES). Through tumor molecular marker targeted sequencing and single-cell transcriptome sequencing, it was found that chromosome 7 copy number variation (CNV) was gained in this cell line, and ZNF804B, EGFR, etc., were overexpressed on chromosome 7. Therefore, RsNF cells can be used as a useful tool in NF1-associated MPNST genomic amplification studies and to develop new therapeutic strategies.

Endoglin, a Novel Biomarker and Therapeutical Target to Prevent Malignant Peripheral Nerve Sheath Tumor Growth and Metastasis

PURPOSE

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive soft-tissue sarcomas that lack effective treatments, underscoring the urgent need to uncover novel mediators of MPNST pathogenesis that may serve as potential therapeutic targets. Tumor angiogenesis is considered a critical event in MPNST transformation and progression. Here, we have investigated whether endoglin (ENG), a TGFβ coreceptor with a crucial role in angiogenesis, could be a novel therapeutic target in MPNSTs.

EXPERIMENTAL DESIGN

ENG expression was evaluated in human peripheral nerve sheath tumor tissues and plasma samples. Effects of tumor cell-specific ENG expression on gene expression, signaling pathway activation and in vivo MPNST growth and metastasis, were investigated. The efficacy of ENG targeting in monotherapy or in combination with MEK inhibition was analyzed in xenograft models.

RESULTS

ENG expression was found to be upregulated in both human MPNST tumor tissues and plasma-circulating small extracellular vesicles. We demonstrated that ENG modulates Smad1/5 and MAPK/ERK pathway activation and pro-angiogenic and pro-metastatic gene expression in MPNST cells and plays an active role in tumor growth and metastasis in vivo. Targeting with ENG-neutralizing antibodies (TRC105/M1043) decreased MPNST growth and metastasis in xenograft models by reducing tumor cell proliferation and angiogenesis. Moreover, combination of anti-ENG therapy with MEK inhibition effectively reduced tumor cell growth and angiogenesis.

CONCLUSIONS

Our data unveil a tumor-promoting function of ENG in MPNSTs and support the use of this protein as a novel biomarker and a promising therapeutic target for this disease.

Malignant peripheral nerve sheath tumor in children: A clinicopathologic and molecular study with parallels to the adult counterpart

Malignant peripheral nerve sheath tumors (MPNST) are aggressive neoplasms, arising either sporadically, in the setting of neurofibromatosis type I (NF1) or post radiation. Most MPNST occur in adults and their pathogenesis is driven by the loss of function mutations in the PRC2 complex, regardless of their clinical presentation. In contrast, pediatric MPNST are rare and their pathogenesis has not been elucidated. In this study, we investigate a large cohort of 64 MPNSTs arising in children and young adults (younger than the age of 20 years) to better define their clinicopathologic and molecular features. Sixteen (25%) cases were investigated by MSK-IMPACT, a targeted NGS panel of 505 cancer genes. Most patients (80%) were aged 11-20 years. A history of NF1 was established in half of the cases. Mean tumor size was 8.5 cm. The most common locations included the extremities (34%) and abdomen/pelvis (27%). Histologically, 89% of high-grade MPNST showed conventional features, while the remaining three cases showed a predominant epithelioid phenotype. Heterologous differentiation occurred in 25% of high grade cases, with half showing rhabdomyoblastic differentiation. Tumors arose in a background of a plexiform neurofibroma (16%), neurofibroma (13%), and schwannoma in two cases (3%). Immunohistochemically, H3K27me3 expression was lost in 82% of conventional high-grade MPNST analyzed, while loss of SMARCB1 expression was seen in one epithelioid MPNST. Genomically, all cases showed more than one genetic abnormality, with 53% showing mutations in EED / SUZ12 genes, and 47% of cases harboring alterations in NF1 and CDKN2A/CDKN2B genes. At the last follow-up, 30% patients died of disease, 28% were alive with disease and 42% had no evidence of disease. NF1 status did not correlate with overall survival. In conclusion, half of pediatric and young adult MPNST were NF1-related and showed loss of function alterations in PRC2 complex, NF1, and CDKN2A, similar to the adult counterpart. Thus, H3K27me3 loss of expression may be used in the diagnosis of high grade MPNSTs in children. Moreover, a small subset of pediatric MPNST have an epithelioid morphology with different pathogenesis.

Malignant peripheral nerve sheath tumor: models, biology, and translation

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, invasive cancer that comprise around 10% of all soft tissue sarcomas and develop in about 8-13% of patients with Neurofibromatosis Type 1. They are associated with poor prognosis and are the leading cause of mortality in NF1 patients. MPNSTs can also develop sporadically or following exposure to radiation. There is currently no effective targeted therapy to treat MPNSTs and surgical removal remains the mainstay treatment. Unfortunately, surgery is not always possible due to the size and location of the tumor, thus, a better understanding of MPNST initiation and development is required to design novel therapeutics. Here, we provide an overview of MPNST biology and genetics, discuss findings regarding the developmental origin of MPNST, and summarize the various model systems employed to study MPNST. Finally, we discuss current management strategies for MPNST, as well as recent developments in translating basic research findings into potential therapies.

Pediatric Gliosarcoma With and Without Neurofibromatosis Type 1: A Whole-exome Comparison of 2 Patients

Gliosarcoma is rare among pediatric patients and among individuals with Neurofibromatosis Type 1 (NF1). Here we compare 2 pediatric gliosarcoma patients, one of whom has NF1. We performed whole-exome sequencing, methylation, and copy number analysis on tumor and blood for both patients. Whole-exome sequencing showed higher mutational burden in the tumor of the patient without NF1. Copy number analysis showed differences in chromosomal losses/gains between the tumors. Neither tumor showed O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation. The NF1 patient survived without progression while the other expired. This is the first reported case of gliosarcoma in a child with NF1.

The Role of Polycomb Repressive Complex in Malignant Peripheral Nerve Sheath Tumor

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft tissue sarcomas that can arise most frequently in patients with neurofibromatosis type 1 (NF1). Despite an increasing understanding of the molecular mechanisms that underlie these tumors, there remains limited therapeutic options for this aggressive disease. One potentially critical finding is that a significant proportion of MPNSTs exhibit recurrent mutations in the genes EED or SUZ12, which are key components of the polycomb repressive complex 2 (PRC2). Tumors harboring these genetic lesions lose the marker of transcriptional repression, trimethylation of lysine residue 27 on histone H3 (H3K27me3) and have dysregulated oncogenic signaling. Given the recurrence of PRC2 alterations, intensive research efforts are now underway with a focus on detailing the epigenetic and transcriptomic consequences of PRC2 loss as well as development of novel therapeutic strategies for targeting these lesions. In this review article, we will summarize the recent findings of PRC2 in MPNST tumorigenesis, including highlighting the functions of PRC2 in normal Schwann cell development and nerve injury repair, as well as provide commentary on the potential therapeutic vulnerabilities of a PRC2 deficient tumor cell.

Genetics of human malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are heterogeneous, highly aggressive tumors with no widely effective treatment other than surgery. Genomic architecture of MPNST is similar to other soft tissue sarcomas, with a relatively modest burden of single nucleotide variants and an elevated frequency of copy-number alterations. Recent advances in genomic studies identified previously unrecognized critical involvement of polycomb repressor complex 2 (PRC2) core components SUZ12 and EED in transition to malignancy. Notably, somatic changes in NF1, CDKN2A/B, and PRC2 are found in most MPNST regardless of their etiology (e.g. neurofibromatosis type 1-associated vs. sporadic vs. radiation-induced), indicating that similar molecular mechanisms impact pathogenesis in these neoplasms. The timing and specific order of genetic or epigenetic changes may, however, explain the typically poorer prognosis of NF1-associated MPNSTs. Studies that reveal genes and regulatory pathways uniquely altered in malignancies are essential to development of targeted tumor therapies. Characterization of MPNST molecular profiles may also contribute to tools for earlier detection, and prediction of prognosis or drug response. Here we review the genetic discoveries and their implications in understanding MPNST biology.

Salvage rates and prognostic factors after relapse in children and adolescents with malignant peripheral nerve sheath tumors

BACKGROUND

Malignant peripheral nerve sheath tumor (MPNST) is one of the most common nonrhabdomyosarcoma soft tissue sarcomas encountered in pediatric age, and it is generally characterized by poor outcome, particularly for relapsing patients.

MATERIALS AND METHODS

This study considered 73 patients <21 years of age with relapsing MPNST observed among 120 patients enrolled in Italian pediatric protocols from 1979 to 2004. With the aim of possibly establishing a risk-adapted stratification, patients' outcome was examined using univariate and multivariate analysis based on clinical features at onset, first-line treatments, clinical findings at the time of first relapse, and second-line treatments.

RESULTS

The time to relapse ranged from 1 to 204 months after first diagnosis (median 7 months). The first relapse event was mainly local. At the time of our analysis, nine patients were alive in remission. The median overall survival after first relapse was 11 months, and the survival rates were 39.2% at 1 year and 15.8% at 5 years. The factors revealing the greatest impact on prognosis were as follows: initial tumor invasiveness, time of relapse, and achievement of a secondary complete remission (which was related to the feasibility of radical surgery).

CONCLUSIONS

Our study confirmed the unsatisfactory prognosis for pediatric patients with relapsing MPNST and pointed to a risk-adapted stratification model for the purposes of deciding second-line treatments. For the time being, an aggressive surgical approach seems to be the only effective salvage treatment and should be recommended. New therapeutic approaches are under evaluation with a view to improving current outcomes.

Dual mTORC1/2 inhibition induces anti-proliferative effect in NF1-associated plexiform neurofibroma and malignant peripheral nerve sheath tumor cells

Approximately 30-50% of individuals with Neurofibromatosis type 1 develop benign peripheral nerve sheath tumors, called plexiform neurofibromas (PNFs). PNFs can undergo malignant transformation to highly metastatic malignant peripheral nerve sheath tumors (MPNSTs) in 5-10% of NF1 patients, with poor prognosis. No effective systemic therapy is currently available for unresectable tumors. In tumors, the NF1 gene deficiency leads to Ras hyperactivation causing the subsequent activation of the AKT/mTOR and Raf/MEK/ERK pathways and inducing multiple cellular responses including cell proliferation. In this study, three NF1-null MPNST-derived cell lines (90-8, 88-14 and 96-2), STS26T sporadic MPNST cell line and PNF-derived primary Schwann cells were used to test responses to AZD8055, an ATP-competitive “active-site” mTOR inhibitor. In contrast to rapamycin treatment which only partially affected mTORC1 signaling, AZD8055 induced a strong inhibition of mTORC1 and mTORC2 signaling in MPNST-derived cell lines and PNF-derived Schwann cells. AZD8055 induced full blockade of mTORC1 leading to an efficient decrease of global protein synthesis. A higher cytotoxic effect was observed with AZD8055 compared to rapamycin in the NF1-null MPNST-derived cell lines with IC50 ranging from 70 to 140 nM and antiproliferative effect was confirmed in PNF-derived Schwann cells. Cell migration was impaired by AZD8055 treatment and cell cycle analysis showed a G0/G1 arrest. Combined effects of AZD8055 and PD0325901 MEK inhibitor as well as BRD4 (BromoDomain-containing protein 4) inhibitors showed a synergistic antiproliferative effect. These data suggest that NF1-associated peripheral nerve sheath tumors are an ideal target for AZD8055 as a single molecule or in combined therapies.

Association Between Juvenile Myelomonocytic Leukemia, Juvenile Xanthogranulomas and Neurofibromatosis Type 1: Case Report and Review of the Literature

The occurrence of juvenile myelomonocytic leukemia (JMML), juvenile xanthogranuloma (JXG), and neurofibromatosis type 1 (NF1) together is relatively rare. Approximately only 20 cases have been reported in the literature. It is debated whether children with NF1 and JXG are at higher risk of developing JMML than children with NF1 alone. We present the case of a boy primarily diagnosed with NF1 with coexisting JXG who developed JMML at the age of 22 months. The clinical course from initial presentation to final diagnosis is detailed and the genetic features and hematologic characteristics are discussed. We report this case to underscore the importance of close monitoring of blood count and strict clinical follow-up in children presenting with concurrent NF1 and JXG and provide a possible explanation for this association.

The NF1 gene in tumor syndromes and melanoma

Activation of the RAS/MAPK pathway is critical in melanoma. Melanoma can be grouped into four molecular subtypes based on their main genetic driver: BRAF-mutant, NRAS-mutant, NF1-mutant, and triple wild-type tumors. The NF1 protein, neurofibromin 1, negatively regulates RAS proteins through GTPase activity. Germline mutations in NF1 cause neurofibromatosis type I, a common genetic tumor syndrome caused by dysregulation of the RAS/MAPK pathway, ie, RASopathy. Melanomas with NF1 mutations typically occur on chronically sun-exposed skin or in older individuals, show a high mutation burden, and are wild-type for BRAF and NRAS. Additionally, NF1 mutations characterize certain clinicopathologic melanoma subtypes, specifically desmoplastic melanoma. This review discusses the current knowledge of the NF1 gene and neurofibromin 1 in neurofibromatosis type I and in melanoma.

Connections between constitutional mismatch repair deficiency syndrome and neurofibromatosis type 1

Constitutional mismatch repair (MMR) deficiency (CMMRD) is a rare childhood cancer susceptibility syndrome resulting from biallelic germline loss-of-function mutations in one of the MMR genes. Individuals with CMMRD have high risk to develop a broad spectrum of malignancies and frequently display features reminiscent of neurofibromatosis type 1 (NF1). Evaluation of the clinical findings of genetically proven CMMRD patients shows that not only multiple café-au-lait macules but also any of the diagnostic features of NF1 may be present in a CMMRD patient. This phenotypic overlap may lead to misdiagnosis of CMMRD patients as having NF1, which impedes adequate management of the patients and their families. The spectrum of CMMRD-associated childhood malignancies includes high-grade glioma, acute myeloid leukaemia or rhabdomyosarcoma, also reported as associated with NF1. Reported associations between NF1 and these malignancies are to a large extent based on studies that neither proved the presence of an NF1 germline mutation nor ruled-out CMMRD in the affected. Hence, these associations are challenged by our current knowledge of the phenotypic overlap between NF1 and CMMRD and should be re-evaluated in future studies. Recent advances in the diagnostics of CMMRD should render it possible to definitely state or refute this diagnosis in these individuals.

The NF1 gene revisited - from bench to bedside

Neurofibromatosis type 1 (NF1) is a relatively common tumour predisposition syndrome related to germline aberrations of NF1, a tumour suppressor gene. The gene product neurofibromin is a negative regulator of the Ras cellular proliferation pathway, and also exerts tumour suppression via other mechanisms.

Recent next-generation sequencing projects have revealed somatic NF1 aberrations in various sporadic tumours. NF1 plays a critical role in a wide range of tumours. NF1 alterations appear to be associated with resistance to therapy and adverse outcomes in several tumour types.

Identification of a patient's germline or somatic NF1 aberrations can be challenging, as NF1 is one of the largest human genes, with a myriad of possible mutations. Epigenetic factors may also contribute to inadequate levels of neurofibromin in cancer cells.

Clinical trials of NF1-based therapeutic approaches are currently limited. Preclinical studies on neurofibromin-deficient malignancies have mainly been on malignant peripheral nerve sheath tumour cell lines or xenografts derived from NF1 patients. However, the emerging recognition of the role of NF1 in sporadic cancers may lead to the development of NF1-based treatments for other tumour types. Improved understanding of the implications of NF1 aberrations is critical for the development of novel therapeutic strategies.

Whole-exome sequencing of breast cancer, malignant peripheral nerve sheath tumor and neurofibroma from a patient with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a genetic disorder characterized by the development of multiple neurofibromas, cafe-au-lait spots, and Lisch nodules. Individuals with NF1 are at increased risk of developing various tumors, such as malignant peripheral nerve sheath tumor (MPNST), pheochromocytoma, leukemia, glioma, rhabdomyosarcoma, and breast cancer. Here, we describe the exome sequencing of breast cancer, MPNST, and neurofibroma from a patient with NF1. We identified a germline mutation in the NF1 gene which resulted in conversion of leucine to proline at amino acid position 847. In addition, we showed independent somatic NF1 mutations in all the three tumors (frameshift insertion in breast cancer (p.A985fs), missense mutation in MPNST (p.G23R), and inframe deletion in dermal neurofibroma (p.L1876del-Inf)), indicating that a second hit in NF1 resulting in the loss of function could be important for tumor formation. Each tumor had a distinct genomic profile with mutually exclusive mutations in different genes. Copy number analysis revealed multiple copy number alterations in the breast cancer and the MPNST, but not the benign neurofibroma. Germline loss of chromosome 6q22.33, which harbors two potential tumor suppressor genes, PTPRK and LAMA2, was also identified; this may increase tumor predisposition further. In the background of NF1 syndrome, although second-hit NF1 mutation is critical in tumorigenesis, different additional mutations are required to drive the formation of different tumors.

Impaired Pten expression in human malignant peripheral nerve sheath tumours

Malignant peripheral nerve sheath tumours (MPNST) are aggressive sarcomas that develop in about 10% of patients with the genetic disease neurofibromatosis type 1 (NF1). Molecular alterations contributing to MPNST formation have only partially been resolved. Here we examined the role of Pten, a key regulator of the Pi3k/Akt/mTOR pathway, in human MPNST and benign neurofibromas. Immunohistochemistry showed that Pten expression was significantly lower in MPNST (n = 16) than in neurofibromas (n = 16) and normal nervous tissue. To elucidate potential mechanisms for Pten down-regulation or Akt/mTOR activation in MPNST we performed further experiments. Mutation analysis revealed absence of somatic mutations in PTEN (n = 31) and PIK3CA (n = 38). However, we found frequent PTEN promotor methylation in primary MPNST (11/26) and MPNST cell lines (7/8) but not in benign nerve sheath tumours. PTEN methylation was significantly associated with early metastasis. Moreover, we detected an inverse correlation of Pten-regulating miR-21 and Pten protein levels in MPNST cell lines. The examination of NF1−/− and NF1+/+Schwann cells and fibroblasts showed that Pten expression is not regulated by NF1. To determine the significance of Pten status for treatment with the mTOR inhibitor rapamycin we treated 5 MPNST cell lines with rapamycin. All cell lines were sensitive to rapamycin without a significant correlation to Pten levels. When rapamycin was combined with simvastatin a synergistic anti-proliferative effect was achieved. Taken together we show frequent loss/reduction of Pten expression in MPNST and provide evidence for the involvement of multiple Pten regulating mechanisms.

High grade malignant peripheral nerve sheath tumors: outcome of 62 patients with localized disease and review of the literature

Malignant peripheral nerve sheath tumours (MPNST) are rare sarcomas with one of the poorest prognoses of all the soft tissue sarcomas. Information about adjuvant treatment is scarce and not homogeneous for this diagnosis. We analyzed retrospectively the outcome of patients with localized high grade MPNST admitted to our institute from 1969 to 2008. A review of the literature is also reported. Of 62 evaluable patients, 23 were females and 39 males, median age 39 years (17-71), 22/62 had neurofibromatosis type I. Median follow-up was 54 months (range 12-194). A total of 22/62 are alive; 26 patients had surgery alone, 18 received radiation therapy, 12 received radiation therapy and chemotherapy, and 6 received only adjuvant chemotherapy. The 5-year disease-free survival was 30% and 5-year overall survival was 38%. A positive trend for adjuvant radiation, but not for chemotherapy was observed according to univariate analysis only for disease-free survival and overall survival. Multivariate analysis indicated that primary site, size and surgical margins remained significant for disease-free survival and only site and size were significant for overall survival. New drugs employed successfully in advanced mpNSt should be employed also in the adjuvant setting.

Molecular cytogenetic analysis of a gliosarcoma with osseous metaplasia

Gliosarcoma, a rare glioblastoma variant, is composed of a glial and a mesenchymal component. Though the mesenchymal portion most commonly resembles a fibrosarcoma, other differentiation patterns have been observed. We present the first genomic characterisation (karyotyping followed by FISH and array comparative genomic hybridisation analysis) of a gliosarcoma with osseous metaplasia. In addition to chromosomal changes often found in gliomas (+7, -10, -13, and -22), the tumour cells also harboured a hitherto unknown t(3;21)(q13∼21;q21∼22).

Clinicopathologic study of glioblastoma in children with neurofibromatosis type 1

BACKGROUND

Neurofibromatosis type 1 (NF1) is characterized by low-grade tumors of the central and peripheral nervous system. There is also an increased risk of developing malignant tumors. Glioblastoma is an uncommon, malignant tumor of children that is even less frequently observed in children with NF1.

PROCEDURE

We performed a retrospective review of patients with NF1 and glioblastoma to determine specific clinical and pathologic indicators of overall prognosis.

RESULTS

Five patients were identified from the CHB/DFCI database for whom pathologic and imaging studies were available. All pathologic specimens demonstrated vascular proliferation and necrosis. All samples stained positively for p53. Chromogenic in situ hybridization (CISH) for epidermal growth factor receptor (EGFR) copy numbers was increased, PTEN copy numbers were normal and the promoter of the O(6)-methylguanine-DNA methyltransferase (MGMT) gene was unmethylated in the one patient evaluated. In the same time period, there were 56 patients without NF1 diagnosed with glioblastoma who were treated at our institution. Although the small sample size precludes formal statistical analysis, the 2-year survival of patients with NF1 is 60% with median overall survival of 9.25 years compared to non-NF1 patients with a 2-year survival of 25% and median overall survival 1.08 years.

CONCLUSIONS

This study provides preliminary evidence that children with NF1 may be at risk for glioblastoma, but that these patients have an increased survival compared to children without NF1. Additional molecular studies will be required to determine if the pathogenesis of these tumors differs from glioblastoma in children without NF1.

Transformation of intracranial anaplastic astrocytoma associated with neurofibromatosis type I into gliosarcoma: case report

Gliosarcoma is an uncommon malignant brain tumor composed of distinct sarcomatous and malignant glial cell elements. These tumors are defined as a variant of glioblastoma, and it can be developed by progression of the malignant glial cell tumors or primary tumors. We report a rare case with gliosarcomatous recurrence of anaplastic astrocytoma with neurofibromatosis type 1 (NF-1) followed by chemoradiation therapy. A 26-year-old male patient was presented with headache. Five years before admission, he had been diagnosed with NF-1. Magnetic resonance imaging (MRI) showed a well-demarcated, enhanced lesion in the right frontal lobe and multiple enhanced lesions in the scalp, lower cervical, thoracic, and upper lumbar regions. He underwent an osteoplastic craniotomy with total tumor resection. Histopathology of the tumor showed findings corresponding with anaplastic astrocytoma. He was followed by radiotherapy and chemotherapy postoperatively. A month later, his spinal lesion was also resected and confirmed pathologically as plexiform neurofibroma. The subsequent follow-up period of 27 months was uneventful until he developed a generalized tonic-clonic seizure. MRI showed tumor recurrence in the original site of the tumor. Re-exploration was carried out. Pathological examination displayed a biphasic pattern of the glial and sarcomatous components suggesting gliosarcoma.

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.

Intestinal neurofibromatosis and small-bowel adenocarcinoma: a single case study

OBJECTIVE

Patients with Von Recklinghausen's disease (neurofibromatosis type 1) are at increased risk of developing various tumours. However, the coexistence of neurofibromatosis with small-bowel adenocarcinoma is exceedingly rare. We present an uncommon case of neurofibromatosis type 1, involving the small bowel in a 73-year-old man, who was admitted to our department with signs of acute abdomen. At laparotomy, multiple mesenteric and intramural nodules were seen in the distal ileum. These nodules obstructed ileal lumen, while the intestine wall was perforated in one point. A wide resection of the affected ileum together with all visible nodules in the adjacent mesentery was performed. Histology revealed neurofibromatosis type 1 with malignant transformation to small-bowel adenocarcinoma. The patient had no additional therapy. In a follow-up of 2 years, the patient is very well and there was no recurrence of the disease. We suggest that adenocarcinoma of small bowel should be considered in the evaluation of acute abdominal pain in neurofibromatosis patients.

Mechanisms in the pathogenesis of malignant tumours in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a familial tumour syndrome. Malignant tumours can arise in the nervous and non-nervous system in either childhood or adulthood, with malignant peripheral nerve sheath tumours being most common. Rhabdomyosarcoma and neuroblastoma are paediatric neoplasms that are more common in children with NF1 than in those without the syndrome. Gastrointestinal stromal tumours, somatostatinomas, breast cancer, and phaeochromocytomas are seen in adults with NF1. Several pathways are thought to be involved in the development of tumours associated with NF1: rat sarcoma viral oncogene homologue (RAS)-mitogen activated protein kinase (MAPK), mammalian target of rapamycin (mTOR), and P21 protein (Cdc42/Rac)-activated kinase 1 (PAK1). New insights into the pathogenesis of these tumours will lead to a better understanding of tumour origin and development and will hopefully allow the discovery of new and specific treatments.

The Neurofibromatosis type 1:A dominantly inherited tumors-predisposing disorder

Neurofibromatosis type I (NF1) is a hereditary multisystem disease involving the skin and nervous system. It is the most common form of autosomal dominant phakomatoses with 100% penetrance but wide phenotypic variability. The NF1 gene is located on chromosome 17q11.2 and encodes for a tumour suppressor protein. Because affected individuals have an increased risk of tumor formation, this disorder is classified as inherited cancer syndrome. The risk of malignancies in NF1 affected patients is estimated to be 5–15% higher than in the general population. We reviewed clinical aspects and genetic mechanisms of tumorigenesis in NF1 affected patients.

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.

Neurofibromin as a regulator of melanocyte development and differentiation

Patients with the genetic disease type I neurofibromatosis (NF1) exhibit characteristic pigmentary lesions associated with loss of a single allele of NF1, encoding the 260 kDa protein neurofibromin. To understand the basis for these pigmentary problems, the properties of melanocytes haploinsufficient for the murine gene Nf1 were studied using Nf1+/– knockout mice. We demonstrate that neurofibromin regulates the Kit-Mitf signaling axis in vivo during melanocyte development. Primary Nf1+/– melanocytes were purified by FACS to measure melanogenic gene expression. We found that Nf1+/– melanocytes exhibit higher levels of melanogenic gene expression than their wild-type counterparts. Both prior to and following Kit stimulation, Nf1+/– melanocytes also exhibit increased activation of the MAP kinase pathway compared with primary cells. The melanogenic response of primary melanocytes to Mek inhibition is consistent with the changes observed with Nf1 haploinsufficiency; however, these changes differ from those observed with their immortalized counterparts. The observation that reduction of neurofibromin, either from haploinsufficiency in the case of primary melanocytes or from neurofibromin knockdown in the case of melan-a cells, enhances melanogenic gene expression suggests that neurofibromin plays a dominant role to MEK activity in controlling melanogenic gene expression in murine melanocytes.

Management of childhood malignant peripheral nerve sheath tumor

Malignant peripheral nerve sheath tumor (MPNST) is rare, but is one of the most frequent non-rhabdomyosarcoma soft-tissue sarcomas in the pediatric population. These tumors occur most frequently at axial sites and are characterized by local aggressiveness and a propensity to metastasize. They are often associated with neurofibromatosis type 1 (NF-1): the lifetime risk of patients with NF-1 developing MPNST has been estimated at 8-13%, compared with 0.001% in the general population. Because of the rarity of this tumor, little information is available on its clinical management, particularly in the pediatric age group. In a recent report on the clinical findings and treatment outcomes from a large number of children and adolescents with MPNST in an Italian and German series, less satisfactory overall outcomes than those for other pediatric sarcomas were described. Therefore, the approach to the treatment of patients with MPNST should be aggressive and risk adapted, and is necessarily complex. Patients should be referred to selected institutions with adequate experience in treating soft-tissue sarcomas, and with the multidisciplinary skills for enrolling patients in clinical trials. Surgical resection represents the mainstay of treatment, while the role of adjuvant treatment is not yet clear. Post-operative radiotherapy seems to have a role in improving local control, although the potential morbidity of irradiation should be taken into account, particularly when treating children. Although lack of local control is the major cause of treatment failure, MPNST may give rise to distant metastases. These tumors are usually considered as having uncertain chemosensitivity, but recent evidence suggests that there may be a role for chemotherapy in patients with a high-grade histology. For the near future, our hopes lie in the development of novel tailored therapies directed specifically against the molecular targets of the neoplastic cells: soft-tissue sarcomas seem particularly promising candidates for targeted therapy.

Soft-tissue sarcomas in children and adolescents with neurofibromatosis type 1

BACKGROUND

Patients affected by neurofibromatosis type 1 (NF1) are at higher risk of developing soft-tissue sarcomas (STS) than the general population. The clinical findings and outcome in 43 children and adolescents with NF1 treated for STS in the Italian protocols between 1988 and 2004 are reported.

METHODS

The study included 37 patients with neurogenic sarcomas (36 malignant peripheral nerve sheath tumors [MPNST], 1 triton tumor) and 6 cases of rhabdomyosarcoma (RMS). The prevalence of NF1 observed during the study period was 43% in the MPNST population and 1% in the RMS group.

RESULTS

Most patients with neurogenic sarcomas had large, invasive tumors. Five-year event-free and overall survival rates were 19% and 28%, respectively. Two of 16 patients with evaluable disease responded to chemotherapy. All 6 RMS patients were </=3 years old and had embryonal subtype, 5 of 6 arising in the genitourinary tract or pelvis (paravesical); 4 were alive in first remission at the time of the analysis, 1 was alive in second remission after a local recurrence, and 1 died of disease.

CONCLUSIONS

The occurrence of STS in pediatric patients with NF1 syndrome in Italy is discussed, confirming that NF1 patients have a high risk of developing STS, and particularly MPNST, often with an aggressive clinical presentation and poor outcome. Cases of RMS tended to have particular features (early age, embryonal histotype, genitourinary site) and their outcome seemed to resemble that of the general RMS population.

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.

Large-scale molecular comparison of human schwann cells to malignant peripheral nerve sheath tumor cell lines and tissues

Malignant peripheral nerve sheath tumors (MPNST) are highly invasive soft tissue sarcomas that arise within the peripheral nerve and frequently metastasize. To identify molecular events contributing to malignant transformation in peripheral nerve, we compared eight cell lines derived from MPNSTs and seven normal human Schwann cell samples. We found that MPNST lines are heterogeneous in their in vitro growth rates and exhibit diverse alterations in expression of pRb, p53, p14(Arf), and p16(INK4a) proteins. All MPNST cell lines express the epidermal growth factor receptor and lack S100beta protein. Global gene expression profiling using Affymetrix oligonucleotide microarrays identified a 159-gene molecular signature distinguishing MPNST cell lines from normal Schwann cells, which was validated in Affymetrix microarray data generated from 45 primary MPNSTs. Expression of Schwann cell differentiation markers (SOX10, CNP, PMP22, and NGFR) was down-regulated in MPNSTs whereas neural crest stem cell markers, SOX9 and TWIST1, were overexpressed in MPNSTs. Previous studies have implicated TWIST1 in apoptosis inhibition, resistance to chemotherapy, and metastasis. Reducing TWIST1 expression in MPNST cells using small interfering RNA did not affect apoptosis or chemoresistance but inhibited cell chemotaxis. Our results highlight the use of gene expression profiling in identifying genes and molecular pathways that are potential biomarkers and/or therapeutic targets for treatment of MPNST and support the use of the MPNST cell lines as a primary analytic tool.

Pediatric malignant peripheral nerve sheath tumor: the Italian and German soft tissue sarcoma cooperative group

PURPOSE

To assess the value of chemotherapy and radiotherapy in children with malignant peripheral nerve sheath tumors (MPNSTs) and to identify risk factors associated with outcome.

PATIENTS AND METHODS

A total of 167 untreated eligible patients enrolled onto the Italian and German studies between 1975 and 1998 entered this analysis. Seventeen percent of patients had neurofibromatosis type 1 (NF1). Chemotherapy was administered to 74% of patients; radiotherapy was administered to 38% of patients.

RESULTS

With a median follow-up of 7 years, 5-year overall survival (OS) and progression-free survival (PFS) were 51% and 37%, respectively. The 5-year OS and PFS by Intergroup Rhabdomyosarcoma Study (IRS) groupings were as follows: group I, 82% and 61%; group II, 62% and 37%; group III, 32% and 27%; group IV, 26% and 21%, respectively. Univariate analysis identified IRS groups, size, invasiveness, primary site, age, and presence of NF1 as prognostic factors; multivariate analysis identified absence of NF1, tumor invasiveness T1, IRS groups I to II and extremity of primary site as independent favorable factors for OS. A trend was observed toward a benefit from radiotherapy after initial gross resection. The overall response rate to primary chemotherapy, including minor responses, in group III patients was 45%.

CONCLUSION

MPNST is an aggressive tumor for which complete surgical resection is the mainstay of successful treatment. Postoperative radiotherapy may have a role in improving local control in patients with minimal residual tumor. The reported responses to primary chemotherapy suggest that it may be effective in patients with tumor considered unresectable at diagnosis.

Expression patterns of cell cycle components in sporadic and neurofibromatosis type 1-related malignant peripheral nerve sheath tumors

The molecular biology underlying the development of highly malignant peripheral nerve sheath tumors (MPNSTs) remains mostly unknown. In the present study, the expression pattern of 10 selected cell cycle components is investigated in a series of 15 MPNSTs from patients with (n = 9) or without (n = 5) neurofibromatosis type 1 (NF1). Thirteen tumors did not express the cyclin-dependent kinase inhibitor, p16(INK4A), an observation that was related to homozygote gene deletions in three tumors, heterozygote deletions in five, and gross gene rearrangements in five. The absence of protein expression in the tumors with one seemingly intact allele was not caused by promoter hypermethylation of p16(INK4A) or p14(ARF). All tumor samples expressed normal sized RB1, cyclin D3, CDK2, CDK4, p21(CIP1), and p27(KlP1) proteins, and only a single tumor showed an aberrant protein band for one of these proteins, p21(CIP1). Cyclin D1 was absent in four tumors; all except one tumor showed expression of TP53 protein, and three of nine MPNSTs had expression of normal-sized MDM2. In conclusion, this study shows that the vast majority of MPNSTs had gross rearrangements of the p16(INK4A) gene, explaining the absence of the encoded protein in the same tumors. The level of expression was equally distributed between the familial (NF1) and sporadic cases, although it should be noted that the 2 cases with p16(INK4A) expression were sporadic. The data imply that the complete absence of p16(INK4A) is sufficient for activation of the cell cycle in most MPNSTs; thus, it is not necessary for tumor proliferation to further stimulate the cycle through alteration of other central components.

La neurofibromatose 1 (NF1) ou maladie de Von Recklinghausen

OBJECTIVES

Neurofibromatosis 1(NF1) is one of the most common genetic diseases. NF1 is an autosomal dominant genetic disorder and half of affected individuals have NF1 as the result of a new gene NF1 mutation. The offspring of an affected individual have a 50% risk of inheriting the altered NF1 gene. The disease manifestations are extremely variable, even within a family. NF1 is characterized by multiple cafe au lait spots, axillary and inguinal freckling, multiple discrete dermal neurofibromas, and iris Lisch nodules. Learning disabilities are frequent. Less common but potentially more serious manifestations include plexiform neurofibromas, optic and other central nervous system gliomas, malignant peripheral nerve sheath tumors, vasculopathy, and osseous lesions.

CURRENT KNOWLEDGES AND KEY POINTS

Since the original National Institutes of Health consensus Development Conference in 1987, there have been significant progress toward a more complete understanding of the molecular-bases for neurofibromatosis 1 and the routine follow-up for the care of the NF1 patients. The authors review the present data on the clinical and molecular aspects of the neurofibromatosis 1.

FUTURE PROSPECTS AND PROJECTS

NF1 requires life-long management adapted to age and multidisciplinary structures are particularly well adapted to the diversity of the manifestations of this pathology. The French NF-France Network has been created in 2001 to federate the French multidisciplinary structures for neurofibromatosis and harmonize the follow-up of NF1 patients in France.

Genetic and phenotypic characterization of tumor cells derived from malignant peripheral nerve sheath tumors of neurofibromatosis type 1 patients

Neurofibromatosis type 1 (NF1) patients have an 8-13% lifetime risk of developing malignant peripheral nerve sheath tumors (MPNST) which have a very poor prognosis. In this study, cells from eight MPNSTs (six primary and two recurrences) of six clinically and genetically well-characterized NF1 patients were taken into culture. Tracing of loss of heterozygosity (LOH) of the NF1, p53, and p16 gene regions or of abnormal karyotypes enabled identification of tumor cells from five MPNSTs. In two other MPNST-derived cell cultures, LOH of the relevant regions in the original tumors could not be detected, indicating that the obtained cells were nonneoplastic cells. Cells from most MPNSTs grew only under standard culture conditions but not under conditions optimized for Schwann cells. These cells were S100-negative and did not exhibit spindle shape which is a characteristic of Schwann cells. Drastically increased proliferation rates were found for most of the MPNST cells in comparison to Schwann cells derived from benign neurofibromas. Our study demonstrates that genetic analysis is effective and essential for verification of MPNST tumor cells in culture. These verified MPNST cells are valuable for further investigations of the biology and pathogenesis of this malignancy as well as for in vitro pharmacologic studies essential for the development of new therapies.

Malignant peripheral nerve sheath tumor with rhabdomyoblastic differentiation (malignant triton tumor) with balanced t(7;9)(q11.2;p24) and unbalanced translocation der(16)t(1;16)(q23;q13)

Malignant peripheral nerve sheath tumors (MPNST) with skeletal muscle differentiation are termed malignant triton tumors. A case of malignant triton tumor arising in a patient without signs of neurofibromatosis with two consistent chromosomal abnormalities is described. The first was of a balanced translocation between the long arm of chromosome 7 and the short arm of chromosome 9. The second was an unbalanced rearrangement between chromosomes 1 and 16, leading to partial trisomy for the long arm of chromosome 1 and partial monosomy for the long arm of chromosome 16. Review of previous reports on chromosomal abnormalities in malignant triton tumors revealed consistent abnormalities involving chromosome 1, regardless of the presence or absence of neurofibromatosis. This finding may relate to the observed poor prognostic outcome in this type of sarcoma. Also unique to our case is the translocation involving 7q and 9p, both regions may play a role in MPNST.

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.

Genetics of Neurofibromatosis 1-Associated Peripheral Nerve Sheath Tumors

Neurofibromatosis 1, an inherited disorder that affects 1/3500 individuals worldwide, predisposes to the development of benign and malignant peripheral nerve sheath tumors. The disorder results from inactivation of one of the NFI genes. The second NFI gene is typically inactivated in Schwann cells during tumor formation. This article reviews the different types of genetic alterations in NFI in both constitutional and tumor tissues and genetic alterations of other genes that may affect tumorigenesis. These studies have provided insight into the genetic basis of both the variable expression of the disorder and of benign and malignant peripheral nerve sheath tumorigenesis.

Modified allelic replication in lymphocytes of patients with neurofibromatosis type 1

Transcription activity of genes is related to their replication timing, accordingly gene activation is coupled with a shift from late replication to early replication and vice versa. The relationship between replication timing and gene expression is best manifested by monoallelically expressed genes which show an asynchronous pattern of allelic replication, with the active allele replicating earlier than the inactive counterpart. Biallelically expressed genes, which normally replicate highly synchronously, when present in lymphocytes derived from patients with various types of malignancies or premalignancies, replicate highly asynchronously, similar to monoallelically expressed genes. Since neurofibromatosis-type 1 (NF1) patients are at an increased risk to develop malignancies, we used the fluorescence in situ hybridization (FISH) replication assay and evaluated the level of replication synchrony of three cancer-implicated genes (RB1, AML1, and CMYC) in lymphocytes derived from patients with NF1 without malignancy. Each gene, which normally displayed synchrony in allelic replication, in the patients' cells displayed loss of synchrony. The loss of replication synchrony, of each gene, in the patients' cells was achieved by an advanced replication of a single allele, which replicated remarkably earlier than its normal scheduled timing. In addition, the second allele showed slightly earlier replication timing than that normal for the gene. Thus, it is assumed that the NF1 condition is associated with activation of cancer-implicated genes that may be the cause for increased risk of patients to develop malignancies. As loss of synchrony in allelic replication timing differentiates well between NF1 patients and control subjects, this marker may have a potential use for identification of presymptomatic carriers of NF1 disorders.

Malignant peripheral nerve sheath tumor cell invasion is facilitated by Src and aberrant CD44 expression

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive malignancies that arise within peripheral nerves. These tumors occur with increased incidence in patients with neurofibromatosis type 1 (NF1), exhibiting increased Ras activity due to loss of the NF1 gene product, neurofibromin, and abnormal expression of the epidermal growth factor receptor (EGFR). We previously found that MPNSTs express increased levels of the CD44 family of transmembrane glycoproteins that have been implicated in tumor cell invasion and metastasis. In two MPNST cell lines, we have found that elevated CD44 expression and cell invasion are dependent on Src kinase activity but are independent of mitogen-activated protein kinases (MAPK) kinase (MEK) activity. In contrast, inhibition of Src kinase activity has no influence on MPNST cell proliferation. Reduction of CD44 levels, using antisense oligonucleotides, results in reduced MPNST cell invasion in vitro, suggesting that Src contributes in part to MPNST cell invasion by increasing CD44 levels. At least some of this increased CD44 expression results from elevated EGFR levels through a Src-dependent mechanism, consistent with the notion that EGFR promotes constitutive Src activation in MPNSTs. These data indicate that Src and CD44 are putative targets for the treatment of MPNST invasion and metastasis.

Pathogenesis of hereditary tumors: beyond the "two-hit" hypothesis

Knudson's 'two-hit' hypothesis has provided extremely important insights into the pathogenesis of tumors in autosomal dominant tumor predisposition syndromes, but recent evidence suggests that some such tumors may occur without a 'second hit' or require more than two mutations. Inactivation of both RB1 alleles appears to be insufficient by itself to cause malignancy in the tumors that develop in patients with hereditary retinoblastoma. On the other hand, certain tumors in patients with tuberous sclerosis complex appear to develop in haploinsufficient tissues that do not have 'second hit' mutations of a tuberous sclerosis gene. The molecular pathogenesis of certain other tumors in patients with tuberous sclerosis complex or neurofibromatosis 1 may not be fully explained by the 'two-hit' hypothesis either. Hereditary tumors, like non-hereditary tumors, may arise by a variety of molecular mechanisms, with loss of both alleles of a particular tumor suppressor gene being a frequent, but not invariably necessary or sufficient, event. Four models are presented to explain how various tumors may arise in patients with inherited tumor predisposition syndromes such as hereditary retinoblastoma, tuberous sclerosis complex or neurofibromatosis 1. Even tumors of one particular type may develop by more than one mechanism.

Frequent genomic imbalances in chromosomes 17, 19, and 22q in peripheral nerve sheath tumours detected by comparative genomic hybridization analysis

Comparative genomic hybridization (CGH) was used to detect changes in relative chromosome copy number in 50 cases of peripheral nerve sheath tumour (PNSTs), including nine malignant peripheral nerve sheath tumours (MPNSTs), 27 neurofibromas (with three plexiform neurofibromas) and 14 schwannomas. Chromosome imbalances were frequently detected in benign as well as malignant PNSTs. In both NF1-associated and sporadic MPNSTs, the number of gains was higher than the number of losses, suggesting proto-oncogene activation during MPNST progression. NF1-asociated MPNSTs exhibited gains of chromosomes 17q and X (2/4 cases each), whereas sporadic MPNSTs showed gains of chromosome 4q (3/5 cases). On the other hand, in benign neurofibromas and schwannomas, the number of losses was higher than the number of gains, suggesting a predominant role of tumour suppressor genes in tumourigenesis. Both sporadic and NF1-associated neurofibromas exhibited losses at chromosome 22q in more than 50% of cases. These chromosomal regions may contain common chromosomal abnormalities characteristic of both types of neurofibromas. In NF1-associated neurofibromas, most frequent losses were found in chromosomes 17 [17p11.2-p13 in nine cases (60%); 17q24-25 in 6 cases (40%)] and 19 [19p13.2 in eight cases (53%); 19q13.2-qter in eight cases (53%)], whereas in sporadic neurofibromas and schwannomas losses of chromosomes 17 and 19 were detected in less than 50% of cases. Since this 17p11.2-p13 region is known to contain the tumour suppressor gene TP53, patients with NF1 may be at high risk of malignant neoplasms including MPNSTs. Gains were more frequently detected in plexiform neurofibromas (2/3 cases) than other benign tumours, suggesting proto-oncogene activation in tumourigenesis of plexiform neurofibroma. The significance of the losses of chromosome 19 in these cases is not clear at present, but in NF1-associated neurofibromas, the presence of some as yet unknown tumour suppressor genes on chromosome 19 cannot be ruled out.

Abdominal migraine in children with neurofibromatosis type 1: a case series and review of gastrointestinal involvement in NF1

BACKGROUND

Symptomatic involvement of the gastrointestinal tract in children with neurofibromatosis type 1 (NF1) is rare. Most reported complications in adults are caused by the presence of neurofibromas in the stomach, small bowel, or mesentery. In contrast, abdominal pain in children with NF1 may be the result of nonanatomic causes, such as migraine. There are no previous reports of an association between abdominal migraine and NF1.

METHODS

Children with abdominal migraine were identified from a group of children with NF1, all of whom had been followed up for a minimum of 3 years. Medical records of cases were reviewed independently by two authors. MEDLINE was searched via PubMed for all reports of children with NF1 and any associated gastrointestinal involvement.

RESULTS

Six children with NF1 and intermittent, episodic, severe abdominal pain are reported. Investigations for obstructive or inflammatory causes of abdominal pain were negative. All patients had previously been diagnosed with migraine headaches by a neurologist. In five of the six patients, propranolol (10-15 mg three times daily) resulted in relief of their abdominal pain within days of starting therapy. Our review identified 24 children in the medical literature with gastrointestinal complications of NF1, mostly secondary to visceral neurofibromas. In almost all of these cases, clinical examination and simple radiologic investigations led to the definitive diagnosis. There were no reports of abdominal migraine complicating NF1.

CONCLUSIONS

Abdominal pain secondary to migraine is an unrecognized cause of abdominal pain in children with NF1 and may be more common than anatomic causes of abdominal pain in children with NF1. In children with NF1 and severe recurrent abdominal pain in whom an evaluation for anatomic lesions is negative, a trial of migraine therapy may be indicated.

Cytogenetic characterization of six malignant peripheral nerve sheath tumors: comparison of karyotyping and comparative genomic hybridization

We analysed six malignant peripheral nerve sheath tumors (MPNSTs) from four patients using metaphase preparations and compared the results with those obtained by using comparative genomic hybridization (CGH). All six tumors showed structural and numerical chromosomal aberrations, mostly of chromosomes 1, 5, 7-10, 14-17, 19, 21, and 22. The number of chromosomes per tumor cell ranged from 42 to 104. We could not find a recurrent specific pattern of structural changes after comparing the MPNSTs of different patients. However, aberrations of different tumors from the same patient were nearly identical. In the four patients, we found a total of 117 breakpoints, mostly in 21q11.2 (seven times), in 8q11.2 and 14q10 (six times each), in 5q11.2 and 15q26 (four times each), in 8p11.2, 10q11.2, 16q22, 19q13.3, and 22q10 (three times each). In three MPNSTs, double minute chromosomes (dmin) we detected with metaphase investigations and high-level amplifications by using CGH, respectively. C-MYC gene amplification and loss of the P53 gene could be ruled out by locus-specific probes for the common gain of 8q and for losses of 17p. When comparing the CGH results with those of karyotyping an overlap in the most frequent gains in 7q, 8q, 15q, and 17q was observed. However, we found more frequent losses in 19q in the metaphase investigations.

Schwann cell proliferative responses to cAMP and Nf1 are mediated by cyclin D1

In most mammalian cells, the cAMP-dependent protein kinase A pathway promotes growth arrest and cell differentiation. However in Schwann cells, the reverse is true. Elevated levels of cAMP function as the cofactor to a broad range of mitogenic cues in culture and in animals. Previous studies have suggested that cAMP acts at an early point in the Schwann cell mitogenic response, perhaps by stimulating the expression of growth factor receptors. We show here that cAMP acts downstream rather than upstream of growth factor receptor expression. The essential function(s) of cAMP is exerted as Schwann cells progress through the G(1) phase of the cell cycle. Ectopic expression studies using an inducible retroviral vector show that the G(1) phase requirement for cAMP can be alleviated by a single protein, cyclin D1. We show, in addition, that at least one function of the Nf1 tumor suppressor is to antagonize the accumulation of cAMP and the expression of cyclin D1 in Schwann cells. Thus a G(1) phase-specific protein, cyclin D1, accounts for two salient features of Schwann cell growth control: the promitotic response to cAMP and the antimitotic response to the Nf1 tumor suppressor.

Rb and TP53 pathway alterations in sporadic and NF1-related malignant peripheral nerve sheath tumors

SUMMARY

Karyotypic complexities associated with frequent loss or rearrangement of a number of chromosome arms, deletions, and mutations affecting the TP53 region, and molecular alterations of the INK4A gene have been reported in sporadic and/or neurofibromatosis type I (NF1)-related malignant peripheral nerve sheath tumors (MPNSTs). However, no investigations addressing possible different pathogenetic pathways in sporadic and NF1-associated MPNSTs have been reported. This lack is unexpected because, despite similar morphologic and immunophenotypic features, NF1-related cases are, by definition, associated with NF1 gene defects. Thus, we investigated the occurrence of TP53 and p16(INK4A) gene deregulation and the presence of microsatellite alterations at markers located at 17p, 17q, 9p21, 22q, 11q, 1p, or 2q loci in MPNSTs and neurofibromas either related (14 cases) or unrelated (14 cases) to NF1. Our results indicate that, in MPNSTs, p16(INK4A) inactivation almost equally affects both groups. However, TP53 mutations and loss of heterozygosity involving the TP53 locus (43% versus 9%), and p53 wild type overexpression, related or not to mdm2 overexpression (71% versus 25%), seem to mainly be restricted to sporadic MPNSTs. In NF1-associated MPNSTs, our microsatellite results are consistent with the occurrence of somatic inactivation by loss of heterozygosity of the second NF1 allele.