Medulloblastoma

The tumor biology and molecular characteristics of medulloblastoma identifying prognostic factors associated with survival outcomes and prognosis

Medulloblastomas (MB) are highly aggressive primitive neuroectodermal tumors (PNET) usually located in the posterior fossa. Current treatment for MBs, which includes a combination of surgery, chemotherapy and radiation, remain challenging especially in younger patients. However, advances in the understanding of regulatory pathways in cerebellar development have elucidated possible areas of dysfunction involved in tumorigenesis. Multiple studies have demonstrated the importance of the sonic hedgehog, Wnt, and Notch pathways in MB pathogenesis at the molecular level. While staging and prognosis are often based on the Chang classification system, future algorithms will involve identifying molecular markers in order to allow for more specific risk stratifications of various MB subtypes and provide improved correlation with staging and prognosis. Future development of novel therapies that target the heterogeneity of MB and are tailored to the tumor's unique molecular profile may yield improved outcomes for these patients.

Characterization of signaling function and expression of HLA class I molecules in medulloblastoma

Although known for the important function in the immune system, MHC class I molecules are increasingly ascribed an alternative role in modifying signal transduction. In medulloblastoma, HLA class I molecules are associated with poor prognosis, and can induce ERK1/2 activation upon engagement with ligands that bind to incompletely assembled complexes (so called open conformers). We here demonstrate that ERK1/2 activation in medulloblastoma can occur in the absence of endogenously synthesized β2m, formally excluding involvement of closed HLA class conformation. In addition, several experimental observations suggest that heterogeneity of HLA class I expression may be a reflection of the status of original cells before transformation, rather than a consequence of immune-based selection of HLA-loss mutants. These results contribute to our understanding of an immune system-independent role of HLA class I in the pathology of medulloblastoma, and cancer in general.

Pharmacokinetic analysis of etoposide distribution after administration directly into the fourth ventricle in a piglet model

We hypothesize that infusion of chemotherapeutic agents directly into the fourth ventricle potentially may play a role in treating malignant posterior fossa brain tumors. Accordingly, we used a piglet model developed in our laboratory to test the safety of etoposide infusions into the fourth ventricle and to study the pharmacokinetics associated with these infusions. In 5 piglets, closed-tip silicone catheters were inserted into the fourth ventricle and lumbar cistern. Five consecutive daily infusions of etoposide (0.5 mg) were administered via the fourth ventricle catheter. Serum and CSF from both catheters were sampled for measurement of etoposide level by reversed-phase high performance liquid chromatography (HPLC). For CSF samples, area under the concentration-time curve (AUC) was calculated. Piglets underwent daily neurological examinations, a 4.7 Tesla MRI scan, and then were sacrificed for post-mortem brain examination. No neurological deficits or signs of meningitis were caused by intraventricular chemotherapy infusions. MRI scans showed catheter placement within the fourth ventricle but no signal changes in the brain stem or cerebellum. In all piglets, the mean fourth ventricular CSF peak etoposide level exceeded the mean peak lumbar etoposide levels by greater than 10-fold. Statistically significant differences between fourth ventricle and lumbar AUC were noted at peaks (DeltaAUC = 3384196 ng h/ml with 95%CI: 1758625, 5009767, P = 0.0044) and at all collection time points (DeltaAUC = 1422977 ng h/ml with 95%CI: 732188, 2113766, P = 0.0046) but not at troughs (DeltaAUC = -29546 ng h/ml (95%CI: -147526, 88434.2, P = 0.5251). Serum etoposide was absent at two and four hours after intraventricular infusions in all animals. Pathological analysis demonstrated meningitis, choroid plexitis, and ependymitis in the fourth and occasionally lateral ventricles. Etoposide can be infused directly into the fourth ventricle without clinical or radiographic evidence of damage. Autopsy examination revealed ventriculitis and meningitis which did not have a clinical correlate. Etoposide does not distribute evenly throughout CSF spaces after administration into the fourth ventricle, and higher peak CSF levels are observed in the fourth ventricle than in the lumbar cistern.

Genetic Analyses Permit the Differentiation Between Reactive Malfunctions (‘Promyelocyte Arrest’) and Arising Promyelocyte Leukemia in a Pregnant Patient With a History of a Medulloblastoma

We report the case of a 24-year-old woman with a history of radiotherapy for a cerebellar medulloblastoma 2 years prior to detection of a lymph node metastasis of the former disease and a pancytopenia in the peripheral blood. On bone marrow (BM) examination promyelocyte leukemia vs. a reactive 'promyelocyte arrest' were discussed. The translocation t(15;17) was found in some nuclei and there was a PML-RARalpha gene rearrangement detectable by RT-PCR. Furthermore, there was BM infiltration by the primary cancer. All these results led to the diagnosis of a relapse of the medulloblastoma and of a beginning promyelocyte leukemia. As the patient was pregnant, she had to be parted with the baby to facilitate intensive chemotherapy. She did not respond to a therapeutic regimen specific for promyelocytic leukemia but achieved complete remission of the medulloblastoma as well as the leukemia after the administration of polychemotherapy specific for medulloblastoma. One year later, she suffered from a relapse of her leukemia. Now nearly all cells showed a t(15;17) aberration. Immunophenotype analyses showed a shift to a more undifferentiated blast phenotype that was, however, still HLA-DR negative. The patient again received chemotherapy for leukemia but developed a sepsis 3 months later and died of pancytopenia ensuing her leukemia. There was no clinical evidence for recurrence of the medulloblastoma.

111In-pentetreotide scintigraphy in medulloblastoma: a comparison with magnetic resonance imaging

Medulloblastoma (MB) is a primitive neuroectodermal tumour constituting a grade IV brain malignancy. Early and correct detection of recurrence or metastasis is desirable for follow-up of patients in this entity. Frequent expression of somatostatin receptors by MB lesions facilitates functional tumour imaging by somatostatin receptor scintigraphy (SRS). To investigate the value of SRS in the follow-up of MB, the results of ten consecutive patients (seven children and three adults) undergoing additional imaging with 111In-pentetreotide were reviewed. Four, 24 and 48 h p.i. planar and whole body images as well as a SPECT study at 4 h p.i. were acquired after intravenous injection of 109 +/- 35 MBq 111In-pentetreotide (Octreoscan). SRS yielded 11 positive and ten negative imaging results, compared to 17 positive and four negative in magnetic resonance imaging (MRI). The lesion-by-lesion analysis with a total of 44 lesions revealed a sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 42%, 83%, 94%, 18% for SRS and 89.5%, 50%, 92%, 43% for MRI. Based on a per-patient analysis, considering the patient as to be either tumour-free or tumour-positive by one imaging modality, the following values for sensitivity, specificity, PPV and NPV were obtained: 61%, 100%, 100%, 30% for SRS and 94%, 67%, 94%, 67% for MRI. MRI remains the first step imaging technique in medulloblastoma patients before and after surgery and during the follow-up providing the highest sensitivity. However, to improve specificity and contribute to correct diagnosis in MB 111In-pentetreotide scintigraphy should be considered as a confirmatory second step imaging tool, especially in case of equivocal MRI results. Moreover, a positive SRS scan might serve as a reference before and after somatostatin receptor targeted radiotherapy.

Hepatocyte growth factor enhances death receptor-induced apoptosis by up-regulating DR5

BACKGROUND

Hepatocyte growth factor (HGF) and its receptor c-MET are commonly expressed in malignant gliomas and embryonic neuroectodermal tumors including medulloblastoma and appear to play an important role in the growth and dissemination of these malignancies. Dependent on cell context and the involvement of specific downstream effectors, both pro- and anti-apoptotic effects of HGF have been reported.

METHODS

Human medulloblastoma cells were treated with HGF for 24-72 hours followed by death receptor ligand TRAIL (Tumor necrosis factor-related apoptosis-inducing ligand) for 24 hours. Cell death was measured by MTT and Annexin-V/PI flow cytometric analysis. Changes in expression levels of targets of interest were measured by Northern blot analysis, quantitative reverse transcription-PCR, Western blot analysis as well as immunoprecipitation.

RESULTS

In this study, we show that HGF promotes medulloblastoma cell death induced by TRAIL. TRAIL alone triggered apoptosis in DAOY cells and death was enhanced by pre-treating the cells with HGF for 24-72 h prior to the addition of TRAIL. HGF (100 ng/ml) enhanced TRAIL (10 ng/ml) induced cell death by 36% (P<0.001). No cell death was associated with HGF alone. Treating cells with PHA-665752, a specific c-Met receptor tyrosine kinase inhibitor, significantly abrogated the enhancement of TRAIL-induced cell death by HGF, indicating that its death promoting effect requires activation of its canonical receptor tyrosine kinase. Cell death induced by TRAIL+HGF was predominately apoptotic involving both extrinsic and intrinsic pathways as evidenced by the increased activation of caspase-3, 8, 9. Promotion of apoptosis by HGF occurred via the increased expression of the death receptor DR5 and enhanced formation of death-inducing signal complexes (DISC).

CONCLUSION

Taken together, these and previous findings indicate that HGF:c-Met pathway either promotes or inhibits medulloblastoma cell death via pathway and context specific mechanisms.

Chemotherapy administration directly into the fourth ventricle in a new piglet model. Laboratory Investigation

OBJECT

The authors hypothesized that chemotherapy infusions directly into the fourth ventricle may potentially play a role in treating malignant posterior fossa tumors. In this study the safety and pharmacokinetics of etoposide administration into the fourth ventricle was tested using an indwelling catheter in piglets.

METHODS

A closed-tip silicone lumbar drain catheter was inserted into the fourth ventricle via a posterior fossa craniectomy and 5 daily infusions of etoposide (0.5 mg in 5 animals) or normal saline (in 2 animals) were instilled. Piglets (10-18 kg, 2-3 months of age) underwent daily neurological examinations and 4.7-T magnetic resonance (MR) imaging after the final infusion and were then killed for postmortem examination. Pharmacokinetics were studied using reversed-phase high-performance liquid chromatography on cerebrospinal fluid (CSF) samples at 0.25, 1, 2, 4, 8, 12, and 24 hours after etoposide infusion. Peak and trough CSF etoposide levels were measured for each subsequent infusion. Serum etoposide levels were obtained at 2 and 4 hours after infusion.

RESULTS

All piglets remained neurologically intact, and MR images demonstrated catheter placement within the fourth ventricle without signal changes in the brainstem or cerebellum. Serum etoposide was absent at 2 and 4 hours after intraventricular infusions. When adequate samples could be obtained for analysis, CSF etoposide levels peaked 15 minutes after infusion and progressively decreased. Cytotoxic levels (> 0.1 microg/ml) were maintained for 5 consecutive peak and trough measurements with 1 exception. Etoposide-related neuropathology included moderate-to-severe T-lymphocytic meningitis and fourth and lateral ventricular choroid plexitis with associated subependymal inflammation.

CONCLUSIONS

Etoposide can be infused directly into the fourth ventricle without clinical or imaging evidence of damage. Cytotoxic CSF etoposide levels can be maintained for 24 hours with a single daily infusion into the fourth ventricle using an indwelling catheter. Intraventricular etoposide elicits an inflammatory response, the long-term effects of which are as yet undetermined.

Antiangiogenic strategies in medulloblastoma: reality or mystery

Medulloblastoma is the most common malignant brain tumor of childhood. Surgery, radiation therapy, and chemotherapy successfully cure many patients, but survivors can suffer long-term toxicities affecting their neurocognitive and growth potential; furthermore, there is no curative therapy in up to 30% of cases, mainly because of our incomplete understanding of many of the underlying molecular and cellular processes. Angiogenesis is a hallmark of the progression of medulloblastoma and, over the last years, investigators have sought to develop effective and less toxic antiangiogenic strategies, including the inhibition or destruction of abnormal blood vessels using either antiangiogenic or vascular disrupting agents. However, the results are conflicting principally because of the complex biology of tumor vasculature and the irregular geometry of the vascular system in real space. In addition, current targets of antiangiogenic therapy, such as vascular endothelial growth factor (VEGF), are thought to be critical for both physiologic and pathologic angiogenesis, and clinical side effects of anti-VEGF therapy are beginning to emerge. We here review the state-of-the-art concerning antiangiogenic targets for medulloblastoma treatment, and discuss the complexity of the vascular system that intrinsically limits the efficacy of current strategies.

The scatter factor/hepatocyte growth factor: c-met pathway in human embryonal central nervous system tumor malignancy

Embryonal central nervous system (CNS) tumors, which comprise medulloblastoma, are the most common malignant brain tumors in children. The role of the growth factor scatter factor/hepatocyte growth factor (SF/HGF) and its tyrosine kinase receptor c-Met in these tumors has been until now completely unknown. In the present study, we show that human embryonal CNS tumor cell lines and surgical tumor specimens express SF/HGF and c-Met. Furthermore, c-Met mRNA expression levels statistically significantly correlate with poor clinical outcome. Treatment of medulloblastoma cells with SF/HGF activates c-Met and downstream signal transduction as evidenced by c-Met, mitogen-activated protein kinase, and Akt phosphorylation. SF/HGF induces tumor cell proliferation, anchorage-independent growth, and cell cycle progression beyond the G1-S checkpoint. Using dominant-negative Cdk2 and a degradation stable p27 mutant, we show that cell cycle progression induced by SF/HGF requires Cdk2 function and p27 inhibition. SF/HGF also protects medulloblastoma cells against apoptosis induced by chemotherapy. This cytoprotective effect is associated with reduction of proapoptotic cleaved poly(ADP-ribose) polymerase and cleaved caspase-3 proteins and requires phosphoinositide 3-kinase activity. SF/HGF gene transfer to medulloblastoma cells strongly enhances the in vivo growth of s.c. and intracranial tumor xenografts. SF/HGF-overexpressing medulloblastoma xenografts exhibit increased invasion and morphologic changes that resemble human large cell anaplastic medulloblastoma. This first characterization establishes SF/HGF:c-Met as a new pathway of malignancy with multifunctional effects in human embryonal CNS tumors.

Conserved mechanisms across development and tumorigenesis revealed by a mouse development perspective of human cancers

Identification of common mechanisms underlying organ development and primary tumor formation should yield new insights into tumor biology and facilitate the generation of relevant cancer models. We have developed a novel method to project the gene expression profiles of medulloblastomas (MBs)--human cerebellar tumors--onto a mouse cerebellar development sequence: postnatal days 1-60 (P1-P60). Genomically, human medulloblastomas were closest to mouse P1-P10 cerebella, and normal human cerebella were closest to mouse P30-P60 cerebella. Furthermore, metastatic MBs were highly associated with mouse P5 cerebella, suggesting that a clinically distinct subset of tumors is identifiable by molecular similarity to a precise developmental stage. Genewise, down- and up-regulated MB genes segregate to late and early stages of development, respectively. Comparable results for human lung cancer vis-a-vis the developing mouse lung suggest the generalizability of this multiscalar developmental perspective on tumor biology. Our findings indicate both a recapitulation of tissue-specific developmental programs in diverse solid tumors and the utility of tumor characterization on the developmental time axis for identifying novel aspects of clinical and biological behavior.

Magnetic resonance imaging findings of an intracranial medulloblastoma in a Polish Lowland Sheepdog

Medullobastoma is an uncommon caudal fossa tumor. The imaging features of medullobastoma in the dog are poorly described. In this report, the magnetic resonance (MR) appearance of a cerebellar medullobastoma in a dog is described. The MR features were similar to medulloblastomas in adult humans, with the tumor arising laterally and extending to the surface of the cerebellar hemisphere. Correct localization of medulloblastoma may be difficult and it should be considered as a differential for both extra- and intra-axial caudal fossa masses.

Classifying the medulloblastoma: insights from morphology and molecular genetics

Significant advances in the treatment of the medulloblastoma (MB) have been made in the last 30 years, reducing mortality by 2-fold. Further improvements in the cure rate require an increased understanding of the biology of MBs, and this will translate into refinements in their classification. Scrutiny of the cytological variation found among MBs has recently led to the concept of the anaplastic MB, which overlaps the large-cell variant and appears to share its poor prognosis. In contrast, the MB with extensive nodularity, a distinctive nodular/desmoplastic variant occurring in infants, has a better outcome than most MBs in these young patients. Building on cytogenetic studies that have drawn attention to abnormalities on chromosome 17 in over a third of MBs, research shows non-random losses on chromosomes 8, 9, 10, 11 and 16, and gains on chromosomes 1, 7 and 9. Overexpression of ErbB2 receptors and losses on chromosome 17p have been proposed as independent indicators of aggressive behaviour, while high TrkC receptor expression indicates a favourable outcome. There is a strong association between anaplastic/large-cell tumours and MYC amplification, which has previously been linked with aggressive disease, but associations between abnormalities on chromosome 17 and anaplastic/large-cell MBs and between abnormalities in the shh/PTCH pathway and the desmoplastic variant are more controversial. Classification of the MB histopathologically and according to profiles of molecular abnormalities will help both to rationalize approaches to therapy, increasing the cure rate and reducing long-term side-effects, and to suggest novel treatments.

Calbindin-d(28k): a marker of recurrence for medulloblastomas

BACKGROUND

The expression of the Ca(2+)-binding protein calbindin-D(28k) was analyzed in medulloblastomas in relation to clinical features and other biologic markers related to cell proliferation, differentiation, p53, and cerebellar developmental regulated gene expression.

METHODS

Immunohistochemistry was carried out on histologic slides from a first retrospective series of 29 nonmetastatic and 10 metastatic medulloblastoma formalin-fixed, paraffin-embedded tissues, using specific antibodies against calbindin-D(28k), calretinin, alpha-parvalbumin and beta-parvalbumin, and S100 proteins. Informed consent was obtained from the subjects and/or guardians. Other biologic markers for differentiation, cell proliferation, the expression of the p53 tumor suppressor gene protein, and cerebellar developmental regulated genes were similarly investigated. A second series of 16 medulloblastomas from young patients (younger than 15 years) was added in order to validate the results obtained in the first series.

RESULTS

Of all the markers investigated, only calbindin-D(28k) was significantly associated with prognosis. Survival and remission (i.e. recurrence free) time analysis performed on all the cases (n = 55) confirmed a high risk of death (P = 0.004) and recurrence (P = 0.003) associated with calbindin-positivity. As calbindin-positivity was predominantly observed in tumors from young patients, the authors confirmed its prognostic value in the subgroup of patients younger than 15 years (n = 37). Cox regression analysis showed a significant and independent prognostic value for calbindin expression and, to a lesser extent, the type of surgery (total or subtotal). Three risk groups were thus identified, distinguishing among the cases characterized by a total resection and calbindin-negativity (good prognosis), by a subtotal resection and calbindin-negativity (intermediary), and by calbindin-positivity (bad prognosis).

CONCLUSIONS

The current study suggests that calbindin-positive medulloblastomas represent a subclass of aggressive tumors more frequently seen in younger patients.

Immunohistochemical markers for prognosis of average-risk pediatric medulloblastomas. The effect of apoptotic index, TrkC, and c-myc expression

Medulloblastomas (MB) are the most common central nervous system malignancies in children. Numerous publications describe certain efforts to identify predictive value of various patterns of MB pathology and immunohistochemistry but received data appear to be controversial. In the present study, the apoptotic index (AI) and immunoexpression of TrkC, and c-myc proteins were investigated in biopsy samples from 68 MB with an average clinical risk to determine their prognostic utility in this tumor category. The number of cases with AI > 1.5% was significantly greater in the group of tumors in patients with recurrent MB and the mean AI was significantly higher in this group -4.7% vs. 1.1%. Furthermore, the number of tumors with AI > 1.5% was greater in the group of tumors in deceased patients and the mean Al was also higher in this group -4.6% vs. 1.2%. Immunoreactivity of the c-myc and TrkC did not show any differences between groups of patients with various clinical outcomes. A close association between Al as a continuous variable and the progression-free and overall survival was found. We found no any differences in survival times for c-myc and TrkC immunoreactivity. Multivariate revealed analysis that AI is a single significant prognostic factor for MB survival. Perhaps, investigations of c-myc and TrkC mRNA levels should be useful for clinical purposes, but in order to introduce these biomolecular markers in clinical protocols its distinct prognostic significance needs to be proved by prospective studies.

A mouse model for medulloblastoma and basal cell nevus syndrome

Medulloblastoma (MB), a tumor of the cerebellum, is the most frequent type of malignant childhood brain tumor. Multiple genes are causally involved in medulloblastoma including PATCHED1 (PTCH). The Patchedl (Ptc1) protein is a receptor for Sonic hedgehog (Shh), a secreted protein ligand. Shh is involved in many signaling processes that control cell fate and growth, among which is its emission from Purkinje cells in the developing cerebellum. Purkinje cell-derived Shh stimulates mitosis of the granule cell precursors that may be the cell type of origin in medulloblastoma. Ptc1 limits the effects of the Shh signal, so mutations in PTCH may lead to persistent granule cell precursors susceptible to further genetic or environmental events that cause medulloblastoma. Mice heterozygous for patched (ptc1) mutations, like heterozygous PTCH humans, have a high rate of medulloblastoma as well as other tumors. We discuss features of the mouse model and how it is contributing to understanding the process of brain tumorigenesis.