Activation of the neuregulin-1/ErbB signaling pathway promotes the proliferation of neoplastic Schwann cells in human malignant peripheral nerve sheath tumors

Patients with neurofibromatosis type 1 develop aggressive Schwann cell neoplasms known as malignant peripheral nerve sheath tumors (MPNSTs). Although tumor suppressor gene mutations play an important role in MPNST pathogenesis, it is likely that dysregulated signaling by as yet unidentified growth factors also contributes to the formation of these sarcomas. To test the hypothesis that neuregulin-1 (NRG-1) growth factors promote mitogenesis in MPNSTs, we examined the expression and action of NRG-1 in human MPNSTs and neurofibromas, the benign precursor lesions from which MPNSTs arise. Multiple alpha and beta transmembrane precursors from the class II and III NRG-1 subfamilies are present in both tumor types. Neoplastic Schwann cells within these neoplasms variably express the erbB kinases mediating NRG-1 responses (erbB2, erbB3 and/or erbB4). Human MPNST cell lines (Mash-1, YST-1, NMS-2 and NMS-2PC cells) similarly coexpress multiple NRG-1 isoforms and erbB receptors. These MPNST lines are NRG-1 responsive and demonstrate constitutive erbB phosphorylation. Treatment with PD168393 and PD158780, two structurally and mechanistically distinct erbB inhibitors, abolishes erbB phosphorylation and reduces DNA synthesis in these lines. These findings suggest that autocrine and/or paracrine NRG-1/erbB signaling promotes neoplastic Schwann cell proliferation and may be an important therapeutic target in neurofibromas and MPNSTs.     

Notch and Schwann cell transformation

Benign plexiform neurofibromas in NF1 patients can transform spontaneously into malignant peripheral nerve sheath tumors (MPNSTs). Although mutations in the p53 gene have been found in a subset of MPNSTs and mouse models support a role for p53 mutations in malignant conversion, we found that each of three Schwann cell lines derived from human MPNSTs possessed active p53. One of the lines expressed the Notch intracellular domain (NICD), indicative of ongoing Notch signaling. Consistent with a role in malignancy, NICD was able to transform primary rat Schwann cells. Transformation was robust--NICD-transduced cells generated tumors in nude rats--and was associated with the loss of markers associated with Schwann cell differentiation. These data suggest that aberrant Notch signaling may contribute to the conversion of benign neurofibromas to MPNSTs.     

MicroRNA-204 critically regulates carcinogenesis in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue sarcomas accounting for 3%-10% of all soft tissue sarcomas. Neurofibromatosis type 1 (NF1) is the most important known risk factor. MPNSTs are often diagnosed at an advanced stage when distant metastases have developed. Although surgical resection remains the main treatment for MPNSTs, complete surgical resection is rarely possible. The prognosis for patients with MPNSTs is poor. There is an urgent need for improved therapies. To this end, we investigated whether microRNA (miR), specifically miR-204, might be implicated in MPNSTs because it is located at a cancer-associated genomic region exhibiting high frequency of loss of heterozygosity in tumors. We show that miR-204 expression is downregulated in NF1 and non-NF1 MPNST tumor tissues and in tumor cell lines. Restoring miR-204 expression in MPNST cell lines STS26T (non-NF1), ST88-14 (NF1), and T265p21 (NF1) significantly reduces cellular proliferation, migration, and invasion in vitro. Restoring miR-204 expression in STS26T decreases tumor growth and malignant progression in vivo. We also report that miR-204 inhibits Ras signaling and expression of high mobility group gene A2. These findings support the hypothesis that miR-204 plays critical roles in MPNST development and tumor progression. miR-204 may represent a novel biomarker for diagnosis and a candidate target with which to develop effective therapies for MPNSTs.     

Fatty acid synthase is a metabolic oncogene targetable in malignant peripheral nerve sheath tumors

BackgroundMalignant peripheral nerve sheath tumors (MPNSTs) are soft tissue sarcomas with minimal therapeutic opportunities. We observed that lipid droplets (LDs) accumulate in human MPNST cell lines and in primary human tumor samples. The goal of this study was to investigate the relevance of lipid metabolism to MPNST survival and as a possible therapeutic target.MethodsBased on preliminary findings that MPNSTs accumulate LDs, we hypothesized that a deregulated lipid metabolism supports MPNST cell survival/proliferation rate. To test this, we examined respiration, role of fatty acid oxidation (FAO), and the enzyme fatty acid synthase involved in de novo fatty acid synthesis in MPNSTs using both genetic and pharmacological tools.ResultsWe demonstrate that LDs accumulate in MPNST cell lines, primary human and mouse MPNST tumors, and neural crest cells. LDs from MPNST cells disappear on lipid deprivation, indicating that LDs can be oxidized as a source of energy. Inhibition of FAO decreased oxygen consumption and reduced MPNST survival, indicating that MPNST cells likely metabolize LDs through active FAO. FAO inhibition reduced oxygen consumption and survival even in the absence of exogenous lipids, indicating that lipids synthesized de novo can also be oxidized. Consequently, inhibition of de novo fatty acid synthesis, which is overexpressed in human MPNST cell lines, effectively reduced MPNST survival and delayed induction of tumor growth in vivo.ConclusionOur results show that MPNSTs depend on lipid metabolic pathways and suggest that disrupting lipid metabolism could be a potential new strategy for the development of MPNST therapeutics.     

Co-targeting the MAPK and PI3K/AKT/mTOR pathways in two genetically engineered mouse models of schwann cell tumors reduces tumor grade and multiplicity

Malignant peripheral nerve sheath tumors (MPNSTs) are soft tissue sarcomas that occur spontaneously, or from benign plexiform neurofibromas, in the context of the genetic disorder Neurofibromatosis Type 1 (NF1). The current standard treatment includes surgical resection, high-dose chemotherapy, and/or radiation. To date, most targeted therapies have failed to demonstrate effectiveness against plexiform neurofibromas and MPNSTs. Recently, several studies suggested that the mTOR and MAPK pathways are involved in the formation and progression of MPNSTs. Everolimus (RAD001) inhibits the mTOR and is currently FDA approved for several types of solid tumors. PD-0325901 (PD-901) inhibits MEK, a component of the MAPK pathway, and is currently in clinical trials. Here, we show in vitro than MPNST cell lines are more sensitive to inhibition of cellular growth by Everolimus and PD-901 than immortalized human Schwann cells. In combination, these drugs synergistically inhibit cell growth and induce apoptosis. In two genetically engineered mouse models of MPNST formation, modeling both sporadic and NF1-associated MPNSTs, Everolimus, or PD-901 treatment alone each transiently reduced tumor burden and size, and extended lifespan. However, prolonged treatment of each single agent resulted in the development of resistance and reactivation of target pathways. Combination therapy using Everolimus and PD-901 had synergistic effects on reducing tumor burden and size, and increased lifespan. Combination therapy allowed persistent and prolonged reduction in signaling through both pathways. These data suggest that co-targeting mTOR and MEK may be effective in patients with sporadic or NF1-associated MPNSTs.     

Tamoxifen inhibits malignant peripheral nerve sheath tumor growth in an estrogen receptor-independent manner

Few therapeutic options are available for malignant peripheral nerve sheath tumors (MPNSTs), the most common malignancy associated with neurofibromatosis type 1 (NF1). Guided by clinical observations suggesting that some NF1-associated nerve sheath tumors are hormonally responsive, we hypothesized that the selective estrogen receptor (ER) modulator tamoxifen would inhibit MPNST tumorigenesis in vitro and in vivo. To test this hypothesis, we examined tamoxifen effects on MPNST cell proliferation and survival, MPNST xenograft growth, and the mechanism by which tamoxifen impeded these processes. We found that 1-5 μM 4-hydroxy-tamoxifen induced MPNST cell death, whereas 0.01-0.1 μM 4-hydroxy-tamoxifen inhibited mitogenesis. Dermal and plexiform neurofibromas, MPNSTs, and MPNST cell lines expressed ERβ and G-protein-coupled ER-1 (GPER); MPNSTs also expressed estrogen biosynthetic enzymes. However, MPNST cells did not secrete 17β-estradiol, exogenous 17β-estradiol did not stimulate mitogenesis or rescue 4-hydroxy-tamoxifen effects on MPNST cells, and the steroidal antiestrogen ICI-182,780 did not mimic tamoxifen effects on MPNST cells. Further, ablation of ERβ and GPER had no effect on MPNST proliferation, survival, or tamoxifen sensitivity, indicating that tamoxifen acts via an ER-independent mechanism. Consistent with this hypothesis, inhibitors of calmodulin (trifluoperazine, W-7), another known tamoxifen target, recapitulated 4-hydroxy-tamoxifen effects on MPNST cells. Tamoxifen was also effective in vivo, demonstrating potent antitumor activity in mice orthotopically xenografted with human MPNST cells. We conclude that 4-hydroxy-tamoxifen inhibits MPNST cell proliferation and survival via an ER-independent mechanism. The in vivo effectiveness of tamoxifen provides a rationale for clinical trials in cases of MPNSTs.     

Efficacy and selectivity of nilotinib on NF1-associated tumors in vitro

Neurofibromatosis type 1 is a tumor suppressor gene disorder which predisposes patients to cutaneous neurofibromas, plexiform neurofibromas (PNFs) and malignant peripheral nerve sheath tumors (MPNSTs) among other neoplasias and manifestation. In this study, we examined the efficiency of nilotinib on PNF-derived Schwann cells and on cells of established MPNST lines in vitro. Nilotinib treatment for 10 days led to decreased proliferation, viability and vitality of the cells with 50 % inhibitory concentration (IC₅₀) for proliferation varying from 3.1 to 9.0 μM. We further addressed selectivity of the drug for tumor cells by simultaneously examining its efficacy on tumor cells (Schwann cells) and non-tumor cells (fibroblasts) from the same tumor. For four out of the six PNFs studied, IC₅₀ was lower in Schwann cells than in fibroblasts for all parameters measured (proliferation, vitality and viability), indicating good drug selectivity. In addition, nilotinib induced apoptosis and suppressed collagenase activity. Our results suggest that nilotinib may provide a treatment option for some PNFs and MPNSTs and our in vitro model of comparative treatment on tumor and non-tumor cells may provide a prototype of preclinical drug screening system toward personalized treatment.     

Protein expression of BIRC5, TK1, and TOP2A in malignant peripheral nerve sheath tumours – A prognostic test after surgical resection

No consensus treatment regime exists beyond surgery for malignant peripheral nerve sheath tumours (MPNST), and the purpose of the present study was to find new approaches to stratify patients with good and poor prognosis and to better guide therapeutic intervention for this aggressive soft tissue cancer.From a total of 67 MPNSTs from Scandinavian patients with and without neurofibromatosis type 1, 30 MPNSTs were investigated by genome‐wide RNA expression profiling and 63 MPNSTs by immunohistochemical (IHC) analysis, and selected genes were submitted to analyses of disease‐specific survival.The potential drug target genes survivin (BIRC5), thymidine kinase 1 (TK1), and topoisomerase 2‐alpha (TOP2A), all encoded on chromosome arm 17q, were up‐regulated in MPNST as compared to benign neurofibromas. Each of them was found to be independent prognostic markers on the gene expression level, as well as on the protein level. A prognostic profile was identified by combining the nuclear expression scores of the three proteins. For patients with completely resected tumours only 15% in the high risk group were alive after two years, as compared to 78% in the low risk group.In conclusion, we found a novel protein expression profile which identifies MPNST patients with inferior prognosis even after assumed curative surgery. The tested proteins are drug targets; therefore the expression profile may provide predictive information guiding the design of future clinical trials. Importantly, as the effect is seen on the protein level using IHC, the biomarker panel can be readily implemented in routine clinical testing.     

MicroRNA‐10b regulates tumorigenesis in neurofibromatosis type 1

MicroRNAs (miRNAs) are frequently deregulated in human tumors, and play important roles in tumor development and progression. The pathological roles of miRNAs in neurofibromatosis type 1 (NF1) tumorigenesis are largely unknown. We demonstrated that miR‐10b was up‐regulated in primary Schwann cells isolated from NF1 neurofibromas and in cell lines and tumor tissues from malignant peripheral nerve sheath tumors (MPNSTs). Intriguingly, a significantly high level of miR‐10b correlated with low neurofibromin expression was found in a neuroectodermal cell line: Ewing’s sarcoma SK‐ES‐1 cells. Antisense inhibiting miR‐10b in NF1 MPNST cells reduced cell proliferation, migration and invasion. Furthermore, we showed that NF1 mRNA was the target for miR‐10b. Overexpression of miR‐10b in 293T cells suppressed neurofibromin expression and activated RAS signaling. Antisense inhibition of miR‐10b restored neurofibromin expression in SK‐ES‐1 cells, and decreased RAS signaling independent of neurofibromin in NF1 MPNST cells. These results suggest that miR‐10b may play an important role in NF1 tumorigenesis through targeting neurofibromin and RAS signaling. (Cancer Sci 2010)     

PTEN and NF1 inactivation in Schwann cells produces a severe phenotype in the peripheral nervous system that promotes the development and malignant progression of peripheral nerve sheath tumors

The genetic evolution from a benign neurofibroma to a malignant sarcoma in patients with neurofibromatosis type 1 (NF1) syndrome remains unclear. Schwann cells and/or their precursor cells are believed to be the primary pathogenic cell in neurofibromas because they harbor biallelic neurofibromin 1 (NF1) gene mutations. However, the phosphatase and tensin homolog (Pten) and neurofibromatosis 1 (Nf1) genes recently were found to be comutated in high-grade peripheral nerve sheath tumors (PNST) in mice. In this study, we created transgenic mice that lack both Pten and Nf1 in Schwann cells and Schwann cell precursor cells to validate the role of these two genes in PNST formation in vivo. Haploinsufficiency or complete loss of Pten dramatically accelerated neurofibroma development and led to the development of higher grade PNSTs in the context of Nf1 loss. Pten dosage, together with Nf1 loss, was sufficient for the progression from low-grade to high-grade PNSTs. Genetic analysis of human malignant PNSTs (MPNST) also revealed downregulation of PTEN expression, suggesting that Pten-regulated pathways are major tumor-suppressive barriers to neurofibroma progression. Together, our findings establish a novel mouse model that can rapidly recapitulate the onset of human neurofibroma tumorigenesis and the progression to MPNSTs.     

EGFR and erbB2 in malignant peripheral nerve sheath tumors and implications for targeted therapy

Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas with poor prognosis and limited treatment options. Evidence for a role of epidermal growth factor receptor (EGFR) and receptor tyrosine kinase erbB2 in MPNSTs led us to systematically study these potential therapeutic targets in a larger tumor panel (n = 37). Multiplex ligation-dependent probe amplification and fluorescence in situ hybridization analysis revealed increased EGFR dosage in 28% of MPNSTs. ERBB2 and three tumor suppressor genes (PTEN [phosphatase and tensin homolog deleted on chromosome 10], CDKN2A [cyclin-dependent kinase inhibitor 2A], and TP53 [tumor protein p53]) were frequently lost or reduced. Reduction of CDKN2A was linked to appearance of metastasis. Comparison of corresponding neurofibromas and MPNSTs revealed an increase in genetic lesions in MPNSTs. No somatic mutations were found within tyrosine-kinase-encoding exons of EGFR and ERBB2. However, at the protein level, expression of EGFR and erbB2 was frequently detected in MPNSTs. EGFR expression was significantly associated with increased EGFR gene dosage. The EGFR ligands transforming growth factor alpha and EGF were more strongly expressed in MPNSTs than in neurofibromas. The effects of the drugs erlotinib and trastuzumab, which target EGFR and erbB2, were determined on MPNST cell lines. In contrast to trastuzumab, erlotinib mediated dose-dependent inhibition of cell proliferation. EGF-induced EGFR phosphorylation was attenuated by erlotinib. Summarized, our data indicate that EGFR and erbB2 are potential targets in treatment of MPNST patients.     

Distinct roles for RB loss on cell cycle control, cisplatin response, and immortalization in Schwann cells

Schwann cells play a critical role in peripheral nerve function. Regulated proliferation of Schwann cells is an important facet of the response to nerve injury; however, aberrant proliferation can give rise to Schwann cell tumors such as malignant peripheral nerve sheath tumors (MPNST). These tumors exhibit a range of genetic lesions that include loss of the retinoblastoma tumor suppressor (RB) pathway. RB plays a critical role in the regulation of cellular proliferation and its loss is a common event in human cancers. Here, the specific action of RB loss on Schwann cell proliferation and response to therapeutic intervention was explored. In primary mouse Schwann cells, conditional RB loss led to increased levels of critical cell cycle regulatory gene products, yet provided only a modest influence on proliferation. However, RB-deficient Schwann cells efficiently bypassed the cell cycle inhibitory response to the chemotherapeutic agent cisplatin, which is used in the treatment of MPNST and other glial tumors. Surprisingly, RB loss did not facilitate Schwann cell immortalization; and RB-deficient cells actually were less prone to immortalization than cells containing RB. Furthermore, RB-deficient cells that ultimately re-entered the cell cycle had lost both Schwann cell morphology and markers. Since, RB loss is likely a late event in Schwann cell tumor progression, the action of acute RB loss in immortalized Schwann cells was investigated. In this context, loss of RB had a profound effect on expression of target genes and the response to cisplatin. Thus, the loss of RB in both primary and immortal Schwann cells disrupted the response to anti-mitogenic signals and has implications for therapeutic intervention.     

Poly (ADP) ribose polymerase inhibition: A potential treatment of malignant peripheral nerve sheath tumor

Poly (ADP) ribose polymerase (PARP) inhibitors, first evaluated nearly a decade ago, are primarily used in malignancies with known defects in DNA repair genes, such as alterations in breast cancer, early onset 1/2 (BRCA1/2). While no specific mutations in BRCA1/2 have been reported in malignant peripheral nerve sheath tumors (MPNSTs), MPNST cells could be effectively targeted with a PARP inhibitor to drive cells to synthetic lethality due to their complex karyotype and high level of inherent genomic instability. In this study, we assessed the expression levels of PARP1 and PARP2 in MPNST patient tumor samples and correlated these findings with overall survival. We also determined the level of PARP activity in MPNST cell lines. In addition, we evaluated the efficacy of the PARP inhibitor AZD2281 (Olaparib) in MPNST cell lines. We observed decreased MPNST cell proliferation and enhanced apoptosis in vitro at doses similar to, or less than, the doses used in cell lines with established defective DNA repair genes. Furthermore, AZD2281 significantly reduced local growth of MPNST xenografts, decreased the development of macroscopic lung metastases, and increased survival of mice with metastatic disease. Our results suggest that AZD2281 could be an effective therapeutic option in MPNST and should be further investigated for its potential clinical use in this malignancy.     

Suppression of proliferation of two independent NF1 malignant peripheral nerve sheath tumor cell lines by the pan-ErbB inhibitor CI-1033

Neurofibromatosis Type 1 (NF1) is characterized by the abnormal proliferation of neuroectodermal tissues and the development of certain tumors, particularly neurofibromas, which may progress into malignant peripheral nerve sheath tumors (MPNSTs). Effective pharmacological therapy for the treatment of NF1 tumors is currently unavailable and the prognosis for patients with MPNSTs is poor. Loss of neurofibromin correlates with increased expression of the epidermal growth factor receptor (EGFR) and ErbB2 tyrosine kinases and these kinases have been shown to promote NF1 tumor-associated pathologies in vivo. We show here that while NF1 MPNST cells have higher EGFR expression levels and are more sensitive to EGF when compared to a non-NF1 MPNST cell line, the ability of the EGFR inhibitor gefitinib to selectively inhibit NF1 MPNST cell proliferation is marginal. We also show that NF1 MPNST proliferation correlates with activated ErbB2 and can be suppressed by nanomolar concentrations of the pan-ErbB inhibitor CI-1033 (canertinib). Consequently, targeting both EGFR and ErbB2 may prove an effective strategy for suppressing NF1 MPNST tumor growth in vivo.     

Analysis of steroid hormone effects on xenografted human NF1 tumor Schwann cells

The neurofibroma, a common feature of neurofibromatosis type 1 (NF1), is a benign peripheral nerve sheath tumor that contains predominantly Schwann cells (SC). There are reports that neurofibroma growth may be affected by hormonal changes, particularly in puberty and pregnancy, suggesting an influence by steroid hormones. This study examined the effects of estrogen and progesterone on proliferation and apoptosis in a panel of NF1 tumor xenografts. SC-enriched cultures derived from three human NF1 tumor types [dermal neurofibroma, plexiform neurofibroma and malignant peripheral nerve sheath tumor (MPNST)] were xenografted in sciatic nerves of ovariectomized scid/Nf1^−/+ mice. At the same time, mice were implanted with time-release pellets for systemic delivery of progesterone, estrogen or placebo. Proliferation and apoptosis by the xenografted SC were examined two months after implantation, by Ki67 immunolabeling and TUNEL. Estrogen was found to increase the growth of all three MPNST xenografts. Progesterone was associated with increased growth in two of the three MPNSTs, yet decreased growth of the other. Of the four dermal neurofibroma xenografts tested, estrogen caused a statistically significant growth increase in one and progesterone did in another. Of the four plexiform neurofibroma SC xenografts, estrogen and progesterone significantly decreased growth in one of the xenografts, but not the other three. No relationship of patient age or gender to steroid response was observed. These findings indicate that human NF1 Schwann cells derived from some tumors show increased proliferation or decreased apoptosis in response to particular steroid hormones in a mouse xenograft model. This suggests that antiestrogen or anti-progesterone therapies may be worth considering for specific NF1 neurofibromas and MPNSTs.Key words: NF1, neurofibroma, steroid hormones, estrogen, xenograft, MPNST, progesterone     

Overexpression of Midkine in malignant peripheral nerve sheath tumor cells inhibits apoptosis and increases angiogenic potency

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft tissue tumors arising sporadically although more frequently in patients with Neurofibromatosis type 1. Prognosis remains dismal as chemo- and radiotherapy have not been shown to be successful. The heparin-binding growth factor, Midkine (MK), is implicated in the tumorigenesis of benign and plexiform neurofibromas, and thereof arising MPNSTs. MK is mitogenic, anti-apoptotic, angiogenic and can promote tumorigenicity in several cell types. Thus, we investigated the role of MK in malignant biology and tumorigenicity in MPNSTs by stable transfection into MPNST cell lines. Overexpression of MK in the MPNST cell line, S462, increased cell viability and protected cells from apoptosis under serum deprivation, but did not induce proliferation. In addition, MK-transfected S462 cells were partially protected from vincristine-induced cell death. Conditioned medium of MK-transfected S462 cells was a potent mitogen for human umbilical venous endothelial cells. Furthermore, MK overexpression in S462 cells was accompanied by higher levels of VEGF mRNA. Yet, stable overexpression of MK in S462 as well as in ST88-14 cells was not sufficient to promote xenograft tumor growth in nude mice. However, increasing survival and enhanced angiogenic potency of MK-transfected S462 cells highlight the importance of developing specific inhibitors for MK as part of new therapeutic concepts against MPNSTs.     

Identification of p53 as a strong predictor of survival for patients with malignant peripheral nerve sheath tumors

The purpose of this study was to identify new prognostic biomarkers with clinical impact in malignant peripheral nerve sheath tumor (MPNST), a highly aggressive malignancy for which no consensus therapy exists besides surgery. We have used tissue microarrays (TMAs) to assess in situ expression of 14 cell-cycle–regulating proteins in 64 well-characterized MPNST patients: 36 sporadic and 28 with neurofibromatosis type 1 (NF1). We developed a new software application for evaluation and logistics of the TMA images and performed a literature survey of cell cycle proteins in MPNST. For NF1-associated patients, there was a clear association between nuclear expression of p53 and poor survival (p = 0.004). Among the other proteins analyzed, we also found significant associations between survival and clinical variables, but none were as strong as that for p53. For the total series of MPNSTs, p53 was shown to be an independent predictor of survival, and patients without remission, with tumor size larger than 8 cm, and with positive p53 expression had a 60 times greater risk of dying within the first 5 years compared with the remaining patients (p = 0.000002). This is the most comprehensive study of in situ protein expression in MPNST so far, and expressed p53 was found to be a strong surrogate marker for outcome. Patients in complete remission with a primary p53-positive MPNST diagnosis may be considered in a high-risk subgroup and candidates for adjuvant treatment.     

p15INK4b, p14ARF, and p16INK4a inactivation in sporadic and neurofibromatosis type 1-related malignant peripheral nerve sheath tumors.

PURPOSE: Malignant peripheral nerve sheath tumor (MPNST) can arise sporadically or in association with neurofibromatosis type 1. Deletions at the 9p21 locus have been reported in these tumors. To additionally characterize the status of this chromosomal region, in this study we performed a comprehensive, mostly PCR-based molecular analysis of the three tumor suppressor genes p15(INK4b), p14(ARF) and p16(INK4a) located at the 9p21 locus in 26 cryopreserved MPNSTs. EXPERIMENTAL DESIGN: Fourteen neurofibromatosis type 1-related and 12 sporadic cases were investigated for homozygous deletion coupled with fluorescent in situ hybridization, promoter methylation, and mutational analysis, as well as m-RNA expression. RESULTS: The results showed that an inactivation of one or more genes occurred in 77% of MPNSTs and was mainly achieved through homozygous deletion (46%), which, in turn, encompassed all of the three tandemly linked genes in 83% of the deleted cases. Promoter methylation was at a less extent involved in gene silencing (18%), and no mutations were found. Loss of function at DNA level strongly correlated with loss of mRNA expression accounting for 80% of the cases. Because of the close relationship between p14(ARF) and TP53 and between p15(INK4b)/p16(INK4a) and Rb, these results support a model of a coinactivation of TP53 and Rb pathways in 75% of MPNSTs, with functional consequences on cell growth control and apoptosis. CONCLUSIONS: The inactivation of the 9p21 locus is a frequent and peculiar hallmark of MPNST genetic profile leading also to an impaired apoptosis that could be taken into account in treatment planning of these tumors.     

Pediatric and adult malignant peripheral nerve sheath tumors: an analysis of data from the surveillance,epidemiology, and end results program

Malignant peripheral nerve sheath tumors (MPNSTs) are rare soft tissue sarcomas that arise predominantly from Schwann cells. Despite the fact that MPNSTs have high local recurrence rates and are generally associated with poor prognosis, little is known about prognostic factors or effective clinical management for this tumor type. The purpose of this study was to describe the distributions of patient and tumor characteristics and to identify predictors of cause-specific survival among MPNST cases reported to SEER between 1973 and 2008. Patient and tumor characteristics were compared between pediatric and adult MPNST cases. Cox regression and tree-based survival analysis were used to examine factors associated with MPNST-related mortality separately among adults and children. A total of 1,315 MPNST cases were isolated from the 1973–2008 SEER dataset. Among pediatric cases, sex, race, and radiation therapy predicted MPNST survival, whereas among adults, tumor site, tumor grade, number of primary tumors, and tumor size were significant predictors. As tumor size at diagnosis/resection may be the only somewhat “modifiable” prognostic factor, future studies should aim to identify biological and social attributes associated with tumor size at diagnosis, separately among individuals with and without NF-1, in order to help identify earlier opportunities for clinical intervention.     

A retroperitoneal NF1-independent malignant peripheral nerve sheath tumor with elevated serum CA125: case report and discussion

Malignant peripheral nerve sheath tumors (MPNSTs) are usually located in the trunk, extremities, head, or neck, and most occur with neurofibromatosis type 1 (NF1; von Recklinghausen's disease). No biomarkers have previously been found to be associated with their progression. Retroperitoneal NF1-independent MPNSTs are rare; they are considered to be less aggressive and to have better prognoses compared to NF1-related tumors. Currently, en bloc excision is the only consensus treatment approach. In a 27-year-old male with a giant retroperitoneal MPNST and no stigmata or family history of neurofibromatosis type-1 (NF1), a remarkable elevation of serum CA125 was detected. The high-grade tumor displayed a striking progression: the primary lesion, 25 cm in diameter, recurred in its previous site as a 17-cm MPNST less than 50 days after total excision. Subsequent treatment with microwave ablation and huachansu, a traditional Chinese medication, proved ineffective, and the patient died within 3 months. Our case suggests that retroperitoneal MPNSTs can deteriorate rapidly even if NF1 independent, that aggressive treatment may not benefit large high-grade MPNSTs, and that novel and effective treatment is urgently needed. Our case also suggests the possibility of using serum tumor markers in the early detection and monitoring of MPNSTs.