The proliferative potential of the pilocytic astrocytoma: the relation between MIB-1 labeling and clinical and neuro-radiological follow-up

Establishment and application of a novel patient-derived KIAA1549:BRAF-driven pediatric pilocytic astrocytoma model for preclinical drug testing

Pilocytic astrocytoma (PA) is the most frequent pediatric brain tumor. Activation of the MAPK pathway is well established as the oncogenic driver of the disease. It is most frequently caused by KIAA1549:BRAF fusions, and leads to oncogene induced senescence (OIS). OIS is thought to be a major reason for growth arrest of PA cells in vitro and in vivo, preventing establishment of PA cultures. Hence, valid preclinical models are currently very limited, but preclinical testing of new compounds is urgently needed. We transduced the PA short-term culture DKFZ-BT66 derived from the PA of a 2-year old patient with a doxycycline-inducible system coding for Simian Vacuolating Virus 40 Large T Antigen (SV40-TAg). SV40-TAg inhibits TP53/CDKN1A and CDKN2A/RB1, two pathways critical for OIS induction and maintenance. DNA methylation array and KIAA1549:BRAF fusion analysis confirmed pilocytic astrocytoma identity of DKFZ-BT66 cells after establishment. Readouts were analyzed in proliferating as well as senescent states, including cell counts, viability, cell cycle analysis, expression of SV40-Tag, CDKN2A (p16), CDKN1A (p21), and TP53 (p53) protein, and gene-expression profiling. Selected MAPK inhibitors (MAPKi) including clinically available MEK inhibitors (MEKi) were tested in vitro. Expression of SV40-TAg enabled the cells to bypass OIS and to resume proliferation with a mean doubling time of 45h allowing for propagation and long-term culture. Withdrawal of doxycycline led to an immediate decrease of SV40-TAg expression, appearance of senescent morphology, upregulation of CDKI proteins and a subsequent G1 growth arrest in line with the re-induction of senescence. DKFZ-BT66 cells still underwent replicative senescence that was overcome by TERT expression. Testing of a set of MAPKi revealed differential responses in DKFZ-BT66. MEKi efficiently inhibited MAPK signaling at clinically achievable concentrations, while BRAF V600E- and RAF Type II inhibitors showed paradoxical activation. Taken together, we have established the first patient-derived long term expandable PA cell line expressing the KIAA1549:BRAF-fusion suitable for preclinical drug testing.

Gamma Knife treatment of low-grade gliomas in children

BACKGROUND

Low-grade gliomas have good overall survival rates in pediatric patients compared to adults. There are some case series that reported the effectiveness and safety of Gamma Knife radiosurgery, yet they are limited in number of patients. We aimed to review the relevant literature for pediatric low-grade glial tumors treated with stereotactic radiosurgery, specifically Gamma Knife radiosurgery, and to present an exemplary case.

CASE DESCRIPTION

A 6-year-old boy was admitted to clinic due to head trauma. He was alert, cooperative, and had no obvious motor or sensorial deficit. A head CT scan depicted a hypodense zone at the right caudate nucleus. The brain magnetic resonance imaging (MRI) depicted a mass lesion at the same location. A stereotactic biopsy was performed. Histopathological diagnosis was low-grade astrocytoma (grade II, World Health Organization (WHO) classification, 2007). Gamma Knife radiosurgery was applied to the tumor bed. Tumor volume was 21.85 cm(3). Fourteen gray was given to 50% isodose segment of the lesion (maximal dose of 28 Gy). The tumor has disappeared totally in 4 months, and the patient was tumor-free 21 months after the initial treatment.

DISCUSSION AND CONCLUSION

The presented literature review represents mostly single-center experiences with different patient and treatment characteristics. Accordingly, a mean/median margin dose of 11.3-15 Gy with Gamma Knife radiosurgery (GKRS) is successful in treatment of pediatric and adult low-grade glial tumor patients. However, prospective studies with a large cohort of pediatric patients should be conducted to make a more comprehensive conclusion for effectiveness and safety of GKRS in pediatric low-grade glial tumors.

Postoperative Surveillance Magnetic Resonance Imaging for Cerebellar Astrocytoma

Introduction:

Patients with low grade astrocytomas generally have good prognosis when total resection can be achieved, but surveillance neuroimaging is commonly performed to detect recurrence or progression. This study evaluated the utility and yield of such strategy for pilocytic and non-pilocytic cerebellar astrocytomas.

Methods:

A 20-year retrospective review was performed of patients undergoing resection of cerebellar astrocytoma at a single institution. A negative MRI string (NMS) ratio was computed as the fraction of total follow-up period over which surveillance neuroimaging was negative for recurrence or progression. Chi-squared analysis differentiated NMS ratio by resection extent and lesion histopathology.

Results:

Twenty-eight patients with pilocytic (n=15) and non-pilocytic (n=13) astrocytoma underwent 34 craniotomies, with total resection in 19 cases. Surveillance MRIs (n=167) among total resection patients were uniformly negative for recurrent disease at average seven years follow-up (NMS ratio = 1.0). The 43 surveillance MRIs among subtotal resection patients revealed disease progression in two patients within six months of operation (NMS ratio = 0.78, p<0.05). No differences in NMS ratio were observed between pilocytic and non-pilocytic astrocytoma subtypes.

Discussion:

This study illustrates pediatric patients with low-grade cerebellar astrocytomas undergoing total resection may not benefit from routine surveillance neuroimaging, primarily because of low recurrence likelihood. Patients with subtotal resection may benefit from surveillance of residual disease, with further work aimed at exploring the schedule of such follow-up.

Pediatric low-grade gliomas: how modern biology reshapes the clinical field

Low-grade gliomas represent the most frequent brain tumors arising during childhood. They are characterized by a broad and heterogeneous group of tumors that are currently classified by the WHO according to their morphological appearance. Here we review the clinical features of these tumors, current therapeutic strategies and the recent discovery of genomic alterations characteristic to these tumors. We further explore how these recent biological findings stand to transform the treatment for these tumors and impact the diagnostic criteria for pediatric low-grade gliomas.

Pathological and molecular advances in pediatric low-grade astrocytoma

Pediatric low-grade astrocytomas are the most common brain tumors in children. They can have similar microscopic and clinical features, making accurate diagnosis difficult. For patients whose tumors are in locations that do not permit full resection, or those with an intrinsically aggressive biology, more effective therapies are required. Until recently, little was known about the molecular changes that drive the initiation and growth of pilocytic and other low-grade astrocytomas beyond the association of a minority of cases, primarily in the optic nerve, with neurofibromatosis type 1. Over the past several years, a wide range of studies have implicated the BRAF oncogene and other members of this signaling cascade in the pathobiology of pediatric low-grade astrocytoma. In this review, we attempt to summarize this rapidly developing field and discuss the potential for translating our growing molecular knowledge into improved diagnostic and prognostic biomarkers and new targeted therapies.

Postoperative imaging surveillance in pediatric pilocytic astrocytomas

OBJECT

Currently there is no consensus regarding the frequency of neuroimaging following gross-total resection (GTR) of pilocytic astrocytoma (PA) in children. Whereas several reports recommend no postoperative imaging, one study proposed surveillance MR imaging studies to detect delayed recurrences.

METHODS

The records of 40 consecutive pediatric patients who underwent GTR of infratentorial PAs were examined. All had follow-up duration of ≥ 2 years. Patients underwent early (< 48 hours) postoperative MR imaging, followed by surveillance imaging at 3-6 months, 1 year, and variably thereafter. The classification of GTR was based on a lack of nodular enhancement on early postoperative MR imaging. Demographic, clinical, and pathological variables were analyzed with respect to recurrence status. Univariate and multivariate analyses were performed to evaluate the association between pathological variables and recurrence-free survival (RFS).

RESULTS

Of 13 patients demonstrating new nodular enhancement on MR imaging at 3-6 months, the disease progressed in 10, with a median time to recurrence of 6.4 months (range 2-48.2 months). At last follow-up, 29 patients had no recurrence, whereas in 1 additional patient the tumor recurred at 48 months, despite the absence of a new contrast-enhancing nodule at 3-6 months (for a total of 11 patients with recurrence). No demographic variable was associated with recurrence. Nodular enhancement on MR imaging at 3-6 months was significantly associated with recurrence in both univariate (p < 0.0001) and multivariate (p = 0.0015) analyses. Among the pathological variables, a high Ki 67 labeling index (LI) was similarly significantly associated with RFS in both univariate (p = 0.0016) and multivariate (p = 0.034) analyses. Multivariate models that significantly predicted RFS included a risk score incorporating Ki 67 LI and CD68 positivity (p = 0.0022), and a similar risk score combining high Ki 67 LI with the presence of nodular enhancement on initial surveillance MR imaging (p < 0.0001).

CONCLUSIONS

Surveillance MR imaging at 3-6 months after resection predicts tumor recurrence following GTR. One patient suffered delayed recurrence, arguing against a "no imaging" philosophy. The data also highlight the pathological variables that can help categorize patients into groups with high or low risk for recurrence. Larger series are needed to confirm these associations.

Activation of the Hedgehog pathway in pilocytic astrocytomas

Pilocytic astrocytoma is commonly viewed as a benign lesion. However, disease onset is most prevalent in the first two decades of life, and children are often left with residual or recurrent disease and significant morbidity. The Hedgehog (Hh) pathway regulates the growth of higher WHO grade gliomas, and in this study, we have evaluated the activation and operational status of this regulatory pathway in pilocytic astrocytomas. Expression levels of the Hh pathway transcriptional target PTCH were elevated in 45% of tumor specimens analyzed (ages 1–22 years) and correlated inversely with patient age. Evaluation of a tissue array revealed oligodendroglioma-like features, pilomyxoid features, infiltration, and necrosis more commonly in specimens from younger patients (below the median patient age of 10 years). Immunohistochemical staining for the Hh pathway components PTCH and GLI1 and the proliferation marker Ki67 demonstrated that patients diagnosed before the age of 10 had higher staining indices than those diagnosed after the age of 10. A significant correlation between Ki67 and PTCH and GLI1 staining indices was measured, and 86% of Ki67-positive cells also expressed PTCH. The operational status of the Hh pathway was confirmed in primary cell culture and could be modulated in a manner consistent with a ligand-dependent mechanism. Taken together, these findings suggest that Hh pathway activation is common in pediatric pilocytic astrocytomas and may be associated with younger age at diagnosis and tumor growth.

Impact of morphology, MIB-1, p53 and MGMT on outcome in pilocytic astrocytomas

Pilocytic astrocytoma (PA) is the most common glioma in the pediatric population. PAs can exhibit variable behavior that does not always correlate with location, yet at present there is no way to predict which tumors will be more aggressive. To address this problem, an institutional cohort of 147 PAs (118 with outcome data) from both cerebellar and noncerebellar locations (spine, diencephalon, midbrain, brainstem and cortex) was utilized. Parameters included quantification of characteristic morphologic variables as well as genes previously shown to be of relevance in high-grade gliomas, including MIB-1, p53 and MGMT. In this cohort, the classic biphasic appearance was most common in cerebellar tumors, whereas noncerebellar tumors were predominantly microcystic. Associations with outcome suggest that the presence of degenerative atypia may be a favorable factor in PAs. Oligodendroglial morphology and the absence of leptomeningeal invasion are adverse histologic factors, but only in cerebellar tumors. Conversely, MIB-1 proliferation index and p53 and MGMT expression do not correlate with outcome. Morphologic biomarkers thus do exist for PAs, but the utility of each biomarker varies according to location. These results suggest that PAs differ fundamentally according to location; therefore, biological behavior may not simply depend on extent of resection.

Hemorrhagic onset of pilocytic astrocytoma and pilomyxoid astrocytoma

The incidence of hemorrhagic onset in pilocytic astrocytoma and pilomyxoid astrocytoma, and the clinical and histological characteristics, were compared to other types of neuroepithelial tumors or nonhemorrhagic pilocytic astrocytoma by retrospective review of 445 consecutive neuroepithelial tumors treated at our institute. Hemorrhagic onset was observed in 4 of 35 (11.4%) patients with pilocytic astrocytoma and pilomyxoid astrocytoma, with higher incidence than in glioblastoma (3.9%), anaplastic oligodendroglioma (7.7%), and anaplastic ependymoma (7.1%). The hemorrhagic onset occurred in 2 patients with sporadic pilocytic astrocytoma, 1 with pilocytic astrocytoma associated with neurofibromatosis type 1, and 1 with pilomyxoid astrocytoma. There was no correlation between hemorrhagic onset and clinical features, including age, sex, tumor location, proliferative activity, or microvascular proliferation. Hemorrhagic onset of pilocytic astrocytoma and pilomyxoid astrocytoma is not as uncommon as was previously thought, so pilocytic astrocytoma or pilomyxoid astrocytoma should be considered in the differential diagnosis of patients with brain tumors manifesting as hemorrhagic onset.

Gene expression profiling of NF-1-associated and sporadic pilocytic astrocytoma identifies aldehyde dehydrogenase 1 family member L1 (ALDH1L1) as an underexpressed candidate biomarker in aggressive subtypes

Pilocytic astrocytomas (PAs) are World Health Organization Grade I gliomas; they most often affect children and young adults and occur in patients with neurofibromatosis type 1 (NF1). To identify genes that are differentially expressed in sporadic (S-PA) versus NF1-associated PAs (NF1-PAs) and those that might reflect differences in clinical behavior, we performed gene expression profiling using Affymetrix U133 Plus2.0 GeneChip arrays in 36 S-PAs and 11 NF1-PAs. Thirteen genes were overexpressed, and another 13 genes were underexpressed in NF1-PAs relative to S-PAs. Immunohistochemical studies performed on 103 tumors, representing 2 independently generated tissue microarrays, confirmed the differential expression of CUGBP2 (p = 0.0014), RANBP9 (p = 0.0075), ITGAV1 (p = 0.0001), and INFGR1 (p = 0.024) proteins. One of the underexpressed genes, aldehyde dehydrogenase 1 family member L1 (ALDH1L1), was also reduced in clinically aggressive compared with typical PAs (p = 0.01) and in PAs with increased cellularity and necrosis. Furthermore, in an additional independent set of tumors, weak to absent ALDH1L1 expression was found in 13 (72%) of 18 clinically aggressive PAs, in 8 (89%) of 9 PAs with pilomyxoid features, in 7 (70%) of 10 PAs with anaplastic transformation, and in 16 (76%) of 21 diffusely infiltrating astrocytomas of various grades. In summary, we have identified a molecular signature that distinguishes NF1-PA from S-PA and found that ALDH1L1 underexpression is associated with aggressive histology and/or biologic behavior.

Expression of oligodendroglial differentiation markers in pilocytic astrocytomas identifies two clinical subsets and shows a significant correlation with proliferation index and progression free survival

The growth pattern of pilocytic astrocytoma (PAs) is unpredictable. Gene expression profiling has recently demonstrated an inverse relationship between myelin basic protein (MBP) expression and progression free survival (PFS) in PAs. We present here the pattern of expression of oligodendroglial differentiation markers (ODMs) in PAs by immunohistochemistry and their correlation with PI and PFS. Sixty-four cases of PA were reviewed and representative sections were stained for Ki-67 and ODMs, including MBP, platelet-derived growth factor receptor-alpha (PDGFR-alpha), Olig-1, and Olig-2. Sections were graded semi-quantitatively for intensity (I: 0-3+) and extent (E: 0-4+) of staining. PI was expressed as a percentage of Ki-67 positive cells. Immunoreactivity of MBP, PDGFR-alpha, Olig-1, and Olig-2 was observed in 84, 56, 97, and 75% of cases, respectively. There was a statistically significant inverse correlation between MBP expression and PI (r (2) = .696, p = .014). A positive correlation was observed between PDGFR-alpha and PI (r (2) = .727, p = .011). Further analysis showed a significant difference in PFS between low expressors [I + E score < or = 3] and high expressors (I + E score > or = 4) for PDGFR-alpha with p < .001. Notably, there was a significant difference in PFS between high expressors of MBP and high expressors of PDGFR-alpha with p < .001. These results suggest that expression of ODMs, especially MBP and PDGFR-alpha, may identify two clinical subsets of PA. In addition, we have shown the expression of 4 different ODMs in PAs, which may support the possibility that PAs arise from oligodendrocyte progenitor/precursor cells probably similar to the O2A progenitor cells in the mouse.

Pilocytic astrocytoma with spontaneous intracranial hemorrhages in an elderly adult

Pilocytic astrocytomas are relatively uncommon tumors found predominantly in the pediatric population. Reports of these tumors are extremely rare in the elderly. This is a report of a 75-year-old man presenting with two spontaneous intracranial hemorrhages and subsequent resection of a pilocytic astrocytoma. The history, evaluation, radiographic features, histopathology, rationale for surgery and potential mechanism of hemorrhage are discussed. A review of the literature summarizes the current field of knowledge of adult pilocytic astrocytomas in the setting of intracranial hemorrhage.

Vascularity and angiogenesis as predictors of growth in optic pathway/hypothalamic gliomas

OBJECT

The authors' aim in conducting this study was to investigate retrospectively the prognostic significance of angiogenic features in optic pathway/hypothalamic gliomas (OPHGs) in children.

METHODS

Patients were identified in whom a diagnosis of OPHG was made using pathological analysis at the Toronto Hospital for Sick Children between 1985 and 2002. Tumor specimens were reviewed for diagnostic accuracy and adequacy of the specimen. Sections were immunostained with factor VIII to assess microvessel density (MVD). A ratio of alpha-smooth muscle actin to factor VIII immunostaining was calculated to arrive at a vascular maturity index (VMI). Vascular endothelial growth factor (VEGF) and VEGF receptor (VEGFR) immunostaining were performed to evaluate angiogenic factors. In addition, the MIB-1 labeling index (LI) was used to assess proliferation. These factors were evaluated with respect to progression-free survival (PFS). Forty-one of 60 patients originally identified had adequate samples and follow up for inclusion in the study. Of these, eight patients had coexisting neurofibromatosis Type 1. Twenty-eight patients experienced tumor progression after the initial treatment (surgery with or without adjuvant treatment). Thirty-eight patients are still alive. A high MVD (> 21 vessels/1.2 mm2) was associated with a significantly higher rate of progression compared with a low MVD (< 21 vessels/1.2 mm2; p = 0.017). Microvessel density was also predictive of reduced PFS on multivariate analysis stratified for extent of resection (p = 0.04), and VMI as well as intensity and distribution of VEGF and VEGFR staining and the MIB-1 LI were not significantly associated with PFS.

CONCLUSIONS

These findings suggest that MVD is the best current predictor of PFS in incompletely resected OPHGs. This information highlights the importance of angiogenesis in regard to low-grade gliomas.

Les astrocytomes pilocytiques du diencéphale de l’enfant

BACKGROUND AND PURPOSE

Pilocytic astrocytoma (PA) is a WHO grade I tumor of the central nervous system mostly arising in children and young adults. Management of diencephalic PA is a difficult challenge. Surgical treatment has to cope with both the difficulties of deep location and eloquent area tumors.

MATERIALS AND METHODS

We retrospectively reviewed seven pediatric cases (female: 4, male: 3) of diencephalic PA. Opto-chiasmatic tumors were excluded from the series. Mean age at diagnosis was 108 months (9 years) (range: 4 month-18 years), median age was 111 months. Median follow-up for the series was 125 months. Tumor locations were as followed: right thalamus: 2, both thalami: 1, hypothalamus: 3, and right basal ganglia: 1. At the onset, the first symptom was mostly raised intracranial pressure. The delay in diagnosis ranged from 48 hours up to 6 years.

TREATMENT

a shunting procedure was performed in 3 patients, a direct surgical approach in 5 patients (gross total removal: 2; partial removal: 3) and one patient had only a biopsy. Three children were re-operated. Three patients were treated by radiationtherapy (RT) after surgery. Chemotherapy was delivered for 4 children.

RESULTS

The overall survival rate was 71.4 months (almost 6 years) (range: 3-184 months). Median survival rate was 42 months (3.5 years). Three children died, two by tumor progression and one death related to late side-effects of RT. Four patients have a good quality of life with GOS I (n = 3) or II (n = 1). We observed tumor regression in two patients at 1 and 17 years after the beginning of treatment. Correct diagnosis was only made for two cases at the initial pathological examination.

CONCLUSION

The course of diencephalic PA is still unpredictable. The tumor can be controlled by a partial surgical removal, and a residual tumor can sometimes decrease in size after surgery. Gross total removal of these tumors, although difficult, may be performed. With cranial navigation systems, the risk is low. Pathological diagnosis is sometimes difficult to assess.

Spontaneous regression of residual low-grade cerebellar pilocytic astrocytomas in children

BACKGROUND

Cerebellar low-grade astrocytomas (CLGAs) of childhood are benign tumours and are usually curable by surgical resection alone or combined with adjuvant radiotherapy.

OBJECTIVE

To undertake a retrospective study of our children with CLGA to determine the optimum schedule for surveillance imaging following initial surgery. In this report we describe the phenomenon of spontaneous regression of residual tumour and discuss its prognostic significance regarding future imaging.

MATERIALS AND METHODS

A retrospective review was conducted of children treated for histologically proven CLGA at Great Ormond Street Hospital from 1988 to 1998.

RESULTS

Of 83 children with CLGA identified, 13 (15.7%) had incomplete resections. Two children with large residual tumours associated with persistent symptoms underwent additional treatment. Eleven children were followed by surveillance imaging alone for a mean of 6.83 years (range 2-13.25 years). Spontaneous tumour regression was seen in 5 (45.5%) of the 11 children. There were no differences in age, gender, symptomatology, histological grade or Ki-67 fractions between those with spontaneous tumour regression and those with progression. There was a non-significant trend that larger volume residual tumours progressed.

CONCLUSIONS

Residual tumour followed by surveillance imaging may either regress or progress. For children with residual disease we recommend surveillance imaging every 6 months for the first 2 years, every year for years 3, 4 and 5, then every second year if residual tumour is still present 5 years after initial surgery. This would detect not only progressive or recurrent disease, but also spontaneous regression which can occur later than disease progression.

Techniques to assess the proliferative potential of brain tumors

Assessment of brain tumor proliferative potential provides important prognostic information that supplements standard histopathologic grading. Many laboratories rely on mitotic figures to quantify the proliferative potential of brain tumors, but this conventional cellular proliferative index is subject to inter-observer variability and not consistently predictive for low-and high-grade tumors. Recent advancements in technology have made it possible to use proliferative indices as a standard supplement in pathology laboratories. Non-invasive tumor tissue measurements of cell proliferation can be performed using- bromodeoxyuridine labeling index (BrdU LI), flow cytometry (FCM), MIB-1 antibody to the Ki-67 antigen (MIB-1), proliferating cell nuclear antigen (PCNA), and argyrophilic nucleolar organizing regions (AgNOR). Each of these assays has been described in the literature with respect to its ability to predict tumor grade or outcome. At the present time MIB-1 and AgNOR are the simplest and most reliable of these techniques. In addition, advances in our understanding of the genetic alterations associated with proliferation promise to provide more specific markers of proliferative potential. Beyond the pathology laboratory, radiographic studies such as positron emission tomography (PET), single photon emission computed tomography (SPECT), and most recently magnetic resonance spectroscopy (MRS) have been used as follow-up measures, assessing response to treatment and tumor recurrence, rather than as predictors of response to treatment. These radiographic tools, however, have the potential to provide an assessment of tumor proliferation without the need for invasive measures. In this article, we present a review of the current techniques utilized to understand the proliferative potential of brain tumors.

Prognosis-related histomorphological and immunohistochemical markers in central nervous system tumors of childhood and adolescence

Brain tumors account for approximately 20% of all childhood cancers, and are the leading cause of cancer morbidity and mortality among children. Although numerous demographic, clinical and therapeutic parameters have been identified over the past few years that have significant prognostic bearing for some pediatric brain tumors, predicting the clinical course and outcome among children with central nervous system tumors is still difficult. A survey of publications on prognosis-related histopathological and immunohistochemical features among pediatric brain tumors revealed 172 series, of which 91 presented statistically significant outcome-associated parameters as defined by a P value of less than 0.05. Most investigations revealing significant prognosis-related markers were performed on medulloblastomas (30 publications), ependymomas (25) and astrocytic tumors (18). In total, 16 cohorts consisted of more than 100 cases (5 on ependymomas, 3 each on medulloblastomas and astrocytic tumors). On the other hand, there were also 13 series with fewer than 20 cases (5 on medulloblastomas). Potentially prognostic histopathological markers vary among different entities and consist of assessment of necroses, mitoses, differentiation, vascular proliferation, and growth pattern, whereas immunohistochemical features include proliferation markers (Ki-67, MIB-1), expression of oncogenes/tumor suppressor genes and their proteins (TP53, c-erbB2), growth factor and hormonal receptors (VEGF, EGFR, HER2, HER4, ErbB-2), cell cycle genes (p27, p14ARF) and cell adhesion molecules, as well as factors potentially related to therapeutic resistance (DNA topoisomerase IIalpha, metallothionein, P-glycoprotein, tenascin). This review discusses the prognostic potential of histopathological and immunohistochemical markers that can be investigated by the practicing neuropathologist as part of the routine diagnostic workload, and scrutinizes their benefit for predicting therapy response and patient outcome among children with brain tumors.

Study of the MIB-1 labeling index as a predictor of tumor progression in pilocytic astrocytomas in children and adolescents

PURPOSE

The pilocytic astrocytoma (PA) is the most common childhood brain tumor. This report examines the MIB-1 labeling index (LI) as a predictor of progression-free survival (PFS) among childhood PAs.

PATIENTS AND METHODS

Consecutive PAs were examined to determine whether the MIB-1 LI was associated with tumor progression. Other variables evaluated included tumor location, use of adjuvant therapy, extent of resection, and age at diagnosis.

RESULTS

One hundred forty-one children were identified (mean +/- SD age, 7.6 +/- 4.7 years; range, 0.43 to 18.56 years); 118 children had adequate tissue for MIB-1 immunohistochemistry. The 5-year PFS was 61.25%. By log-rank analysis, an MIB-1 LI of more than 2.0 was associated with shortened PFS (P =.035). Patients with PAs who underwent complete surgical resection, had tumors located in the cerebellum, and were treated with surgery only also had more prolonged PFS (P =.001 for all). Tumors in the optic pathways were associated with a shorter PFS (P =.001). Restricting the evaluation of MIB-1 LI to only incompletely resected tumors revealed an insignificant trend of MIB-1 LI of more than 2.0 having a shortened PFS. Multivariate analysis demonstrated completely resected tumors and tumors located in the cerebellum as less likely to progress (P =.001 and.019, respectively).

CONCLUSION

Children with PAs with an MIB-1 LI of more than 2.0 have a shortened PFS. PAs that are completely resected and are located in the cerebellum have a prolonged PFS. This initial study suggests that the MIB-1 LI identifies a more aggressive subset of PAs. Further work should focus on elucidating features of pilocytic astocytomas that will identify prospectively children at risk for progression.

Enhanced apoptosis in pilocytic astrocytoma: a comparative study of apoptosis and proliferation in astrocytic tumors

Both cell proliferation and cell death occur simultaneously in tumor tissue, and extent of tumor growth reflects the net balance of these events. We correlated cell proliferation, spontaneous cell death, and alterations in tumor suppressor proteins with one another and with survival of patients with primary astrocytic tumors. In 39 astrocytic tumor specimens (6 pilocytic astrocytomas, 14 fibrillary astrocytomas, 9 anaplastic astrocytomas, and 10 glioblastomas), we determined the MIB-1 labeling index, the apoptotic ratio according to nick end labeling with morphologic confirmation, the p53 labeling index, and the presence of p53 or PTEN mutations. MIB- I labeling indices of pilocytic astrocytomas, fibrillary astrocytomas, anaplastic astrocytomas, and glioblastomas were 0.30+/-0.32; 1.84+/-1.87; 19.3+/-6.42; and 28.0+/-14.5 (mean +/- SD), respectively. Corresponding apoptotic ratios were 17.9+/-5.16; 3.96+/-3.57; 1.18+/-0.93; and 2.11+/-1.60 (mean +/- SD). The apoptotic ratio in pilocytic astrocytomas was significantly higher than in other astrocytic tumors (fibrillary astrocytomas, p < 0.05; anaplastic astrocytomas and glioblastomas, p < 0.01). MIB-1 showed a significant negative correlation with apoptosis (p < 0.01). MIB- I and apoptosis showed significant negative and positive correlations with patient survival (p < 0.01). Mutations of p53 and PTEN show no correlation with survival and apoptotic ratio. The apoptotic ratio can clearly distinguish pilocytic astrocytomas from other tumors, and this biological feature may reflect less aggressive growth of pilocytic astrocytomas.

Ki-67: a prognostic factor for low-grade glioma?

PURPOSE

Immunohistochemical techniques were used to detect the expression of Ki-67, a nuclear proliferation marker, in 180 low-grade glioma tumor specimens to determine whether Ki-67 is a prognostic predictor of survival or tumor recurrence.

MATERIALS AND METHODS

A clinical database of 180 low-grade glioma patients (35 children aged </=18 years and 145 adults) was compiled. Eighty patients had received postoperative radiotherapy (RT) and 100 patients had had RT deferred until the time of tumor progression/recurrence. Ki-67 indexes were evaluated retrospectively on tumor specimens from these patients using a semiautomated computer analysis technique. Ten observations were averaged per patient. The maximal Ki-67 value was recorded.

RESULTS

The correlation between the Ki-67 index and survival was much higher for the averaged Ki-67 value than for the maximal value. Of the tumor specimens, 29% had a negative Ki-67 index (i.e., zero Ki-67 positive cells) and 7.7% had an average Ki-67 index of >/=5%. An average Ki-67 value of >/=5% was prognostically significant for reduced cause-specific survival (CSS, p = 0.05) and a Ki-67 level >/=10% was strongly significant of a poor survival outcome (p = 0.009). Ki-67 was not prognostically significant for progression-free survival. Other prognostically significant factors for CSS included age (p = 0.05), Karnofsky performance status (p = 0.0001), radiation dose (p = 0.02), extent of surgical resection (biopsy vs. others, p = 0.004), and timing of radiation (p = 0.0005). Ki-67 did not remain an independent statistically significant factor for CSS on multivariate analysis. Age and Ki-67 positivity (both maximal and average values) directly correlated (i.e., advancing age was associated with a higher Ki-67 index). When the patient group was further subdivided by age and timing of RT (postoperative vs. deferred), the prognostic significance of Ki-67 for CSS was lost. Within the deferred RT subgroup, a maximal Ki-67 >2% was associated with a worsened CSS. Within the pediatric population, Ki-67-negative patients had a 5-year CSS and progression-free survival of 100%. The 5-year CSS and progression-free survival declined significantly to 84% and 67% for patients with tumors demonstrating any degree of Ki-67 positivity (p = 0.005 and p = 0.006, respectively).

CONCLUSION

Ki-67 is a useful predictor of CSS in low-grade gliomas; however, it is not independent of other prognostic factors, particularly age. Although Ki-67 was not helpful in predicting which adult patients were likely to benefit from postoperative RT, the results of the present study indicate a possible utility in the selection of pediatric patients for RT and in the selection of poorer prognosis patients for clinical trials.

DNA topoisomerase IIalpha expression in optic pathway gliomas of childhood

DNA topoisomerase IIalpha (Topo IIalpha) is linked to tumour cell growth and chemoresistance. We examined immunohistochemically Topo IIalpha expression levels in a series of 36 consecutive paediatric optic pathway glioma (OPG) patients. Topo IIalpha labelling index (LI) ranged from 0.0 to 11.6 and was significantly associated with patient age, with higher levels of Topo IIalpha in children < or = 3 years (P=0.031). Topo IIalpha expression did not correlate with patient survival. Topo IIalpha LI was not significantly increased in specimens of repeat surgery. Topo IIalpha LI closely correlated with MIB-1 LI (R=0.781, P<0.001). We conclude that Topo IIalpha expression correlates with tumour cell proliferation in paediatric OPGs. Assessment of cell proliferation, however, does not assist in refining prognostic predictions. Enhanced Topo IIalpha expression in children < or = 3.0 years suggests that Topo IIalpha-interfering anticancer compounds for adjuvant treatment of OPGs may be of particular benefit to young children.

Prognostic significance of Ki-67 (MIB-1) proliferation index in childhood primitive neuroectodermal tumors of the central nervous system

BACKGROUND

Primitive neuroectodermal tumors (PNET) of the central nervous system, including medulloblastomas, are the most common malignant brain tumors of childhood. Whereas some patients experience prolonged disease control after surgery and adjuvant therapy, others with tumors that appear comparable will relapse and eventually die from progressive disease.

PROCEDURE

Because proliferative activity may provide a potential correlate of biologic aggressiveness, PNETs of 78 well-characterized patients were evaluated by Ki-67 (MIB-1) immunohistochemistry. Proliferation indices (PI) were determined by counting Ki-67 (MIB-1) positive tumor cells either in the highest staining region (hot spot PI), or in at least 15 randomly chosen fields (random PI).

RESULTS

Twenty-five of 78 PNETs showed amore than twofold higher value of hot spot PI (median 9.3%; range 0.6-56%), compared to random PI (median 5.6%; range 0.2-41.3%), Univariate Cox regression analysis revealed that PNETs with a high hot spot PI had a significantly greater risk of progression and death than PNETs with a low hot spot PI (hazard ratio 1.58, P = 0.04). The hazard ratio remained significant after adjusting for M-stage in multivariate analysis. In contrast to hot spot PI, random PI proved not to be a significant prognostic predictor.

CONCLUSIONS

Hot spot PI is a significant and independent prognostic factor in PNETs. Its assessment is uncomplicated, reliable, and may supplement routine histologic examination as a means for improving the accuracy of predicting the biologic behavior of childhood PNETs.

Brain tumor invasion rate measured in vitro does not correlate with Ki-67 expression

The need for more accurate prediction of the biological behavior of brain tumors has lead to the use of immunohistochemical methods for assessment of proliferating cell nuclear antigens such as Ki-67. There is a variable association of glioma Ki-67 labeling index with patient survival. Brain invasion by individual tumor cells also defines biological aggressiveness, and can be assessed in vitro. Further, proliferation and migration seem to be mutually exclusive behaviors for a given cell at a point in time. We studied the relationship between Ki-67 labeling index and invasion rate in a group of 10 gliomas, and 2 meningiomas. Human tumor spheroids obtained from operative specimen were co-cultured with fetal rat brain aggregates, and invasion rate was measured by confocal microscopic observation. There was no correlation between two measures of invasion and Ki-67 labeling. This finding supports the dichotomous nature of glioma proliferation and invasion, and may in part explain the limited usefulness of proliferation marker labeling.