The fourth edition of the World Health Organization (WHO) classification of tumours of the central nervous system, published in 2007, lists several new entities, including angiocentric glioma, papillary glioneuronal tumour, rosette-forming glioneuronal tumour of the fourth ventricle, papillary tumour of the pineal region, pituicytoma and spindle cell oncocytoma of the adenohypophysis. Histological variants were added if there was evidence of a different age distribution, location, genetic profile or clinical behaviour; these included pilomyxoid astrocytoma, anaplastic medulloblastoma and medulloblastoma with extensive nodularity. The WHO grading scheme and the sections on genetic profiles were updated and the rhabdoid tumour predisposition syndrome was added to the list of familial tumour syndromes typically involving the nervous system. As in the previous, 2000 edition of the WHO ‘Blue Book’, the classification is accompanied by a concise commentary on clinico-pathological characteristics of each tumour type. The 2007 WHO classification is based on the consensus of an international Working Group of 25 pathologists and geneticists, as well as contributions from more than 70 international experts overall, and is presented as the standard for the definition of brain tumours to the clinical oncology and cancer research communities world-wide.

https://link.springer.com/content/pdf/10.1007%2Fs00401-007-0243-4.pdf

The 2007 WHO Classification of Tumours of the Central Nervous System

The new World Health Organization (WHO) classification of nervous system tumors, published in 2000, emerged from a 1999 international consensus conference of neuropathologists. New entities include chordoid glioma of the third ventricle, cerebellar liponeurocytoma, atypical teratoid/rhabdoid tumor, and perineurioma. Several histological variants were added, including tanycytic ependymoma, large cell medulloblastoma, and rhabdoid meningioma. The WHO grading scheme was updated and, for meningiomas, extensively revised. In recognition of the emerging role of molecular diagnostic approaches to tumor classification, genetic profiles have been emphasized, as in the distinct subtypes of glioblastoma and the already clinically useful 1p and 19q markers for oligodendroglioma and 22q/INI1 for atypical teratoid/rhabdoid tumors. In accord with the new WHO Blue Book series, the actual classification is accompanied by extensive descriptions and illustrations of clinicopathological characteristics of each tumor type, including molecular genetic features, predictive factors, and separate chapters on inherited tumor syndromes. The 2000 WHO classification of nervous system tumors aims at being used and implemented by the neuro-oncology and biomedical research communities worldwide.

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The WHO Classification of Tumors of the Nervous System

Background/methods Gliomas are common malignant neoplasms of the central nervous system. Among the major subtypes of gliomas, oligodendrogliomas are distinguished by their remarkable sensitivity to chemotherapy, with approximately two thirds of anaplastic (malignant) oligodendrogliomas responding dramatically to combination treatment with procarbazine, lomustine, and vincristine (termed PCV). Unfortunately, no clinical or pathologic feature of these tumors allows accurate prediction of their response to chemotherapy. Anaplastic oligodendrogliomas also are distinguished by a unique constellation of molecular genetic alterations, including coincident loss of chromosomal arms 1p and 19q in 50%-70% of tumors. We have hypothesized that these or other specific genetic changes might predict the response to chemotherapy and prognosis in patients with anaplastic oligodendrogliomas. Therefore, we have analyzed molecular genetic alterations involving chromosomes 1p, 10q, and 19q and the TP53 (on chromosome 17p) and CDKN2A (on chromosome 9p) genes, in addition to clinicopathologic features in 39 patients with anaplastic oligodendrogliomas for whom chemotherapeutic response and survival could be assessed. Results/conclusions Allelic loss (or loss of heterozygosity) of chromosome 1p is a statistically significant predictor of chemosensitivity, and combined loss involving chromosomes 1p and 19q is statistically significantly associated with both chemosensitivity and longer recurrence-free survival after chemotherapy. Moreover, in both univariate and multivariate analyses, losses involving both chromosomes 1p and 19q were strongly associated with longer overall survival, whereas CDKN2A gene deletions and ring enhancement (i.e., contrast enhancement forming a rim around the tumor) on neuroimaging were associated with a significantly worse prognosis. The inverse relationship between CDKN2A gene deletions and losses of chromosomes 1p and 19q further implies that these differential clinical behaviors reflect two independent genetic subtypes of anaplastic oligodendroglioma. These results suggest that molecular genetic analysis may aid therapeutic decisions and predict outcome in patients with anaplastic oligodendrogliomas.

Specific Genetic Predictors of Chemotherapeutic Response and Survival in Patients With Anaplastic Oligodendrogliomas

Glioblastoma is the most frequent and most malignant human brain tumor. The prognosis remains very poor, with most patients dying within 1 year after diagnosis. Primary and secondary glioblastoma constitute distinct disease subtypes, affecting patients of different age and developing through different genetic pathways. The majority of cases (>90%) are primary glioblastomas that develop rapidly de novo, without clinical or histological evidence of a less malignant precursor lesion. They affect mainly the elderly and are genetically characterized by loss of heterozygosity 10q (70% of cases), EGFR amplification (36%), p16INK4a deletion (31%), and PTEN mutations (25%). Secondary glioblastomas develop through progression from low-grade diffuse astrocytoma or anaplastic astrocytoma and manifest in younger patients. In the pathway to secondary glioblastoma, TP53 mutations are the most frequent and earliest detectable genetic alteration, already present in 60% of precursor low-grade astrocytomas. The mutation pattern is characterized by frequent G:C→A:T mutations at CpG sites. During progression to glioblastoma, additional mutations accumulate, including loss of heterozygosity 10q25-qter (∼70%), which is the most frequent genetic alteration in both primary and secondary glioblastomas. Primary and secondary glioblastomas also differ significantly in their pattern of promoter methylation and in expression profiles at RNA and protein levels. This has significant implications, particularly for the development of novel, targeted therapies, as discussed in this review.

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Genetic Pathways to Primary and Secondary Glioblastoma

Despite aggressive surgery, radiotherapy and chemotherapy, malignant gliomas remain uniformly fatal. To progress, these tumours stimulate the formation of new blood vessels through processes driven primarily by vascular endothelial growth factor (VEGF). However, the resulting vessels are structurally and functionally abnormal, and contribute to a hostile microenvironment (low oxygen tension and high interstitial fluid pressure) that selects for a more malignant phenotype with increased morbidity and mortality. Emerging preclinical and clinical data indicate that anti-VEGF therapies are potentially effective in glioblastoma — the most frequent primary brain tumour — and can transiently normalize tumour vessels. This creates a window of opportunity for optimally combining chemotherapeutics and radiation.

Angiogenesis in brain tumours

Introduction Histological Classification of CNS Tumours Definitions and Explanatory Notes Tumours of Neuroepithelial Tissue Astrocytic Tumours Ependymal Tumours Mixed Gliomas Choroid Plexus Tumours Neuroepithelial Tumours of Uncertain Origin Neuronal and Mixed Neuronal-Glial Tumours Pineal Parenchymal Tumours Embryonal Tumours Tumours of Cranial and Spinal Nerves Schwannoma Neurofibroma Malignant Peripheral Nerve Sheath Tumor Tumours of the Meninges Tumours of Menigothelial Cells Mesenchymal, Non-menigothelial Tumours Primary Melanocytic Lesions Lymphomas and Haemopoietic Neoplasms Germ Cell Tumours Cysts and Tumour-like Lesions Tumours of the Sellar Region Local Extensions from Regional Tumours Metastatic Tumours Unclassified Tumours Illustrations Subject Index Metat Cy Tu

O. G. Dodge

Papers

Histological Typing of tumours of the Central Nervous System