Hiroko Ohgaki

International Society of Neuropathology‐Haarlem Consensus Guidelines for Nervous System Tumor Classification and Grading

Major discoveries in the biology of nervous system tumors have raised the question of how non‐histological data such as molecular information can be incorporated into the next World Health Organization (WHO) classification of central nervous system tumors. To address this question, a meeting of neuropathologists with expertise in molecular diagnosis was held in Haarlem, the Netherlands, under the sponsorship of the International Society of Neuropathology (ISN). Prior to the meeting, participants solicited input from clinical colleagues in diverse neuro‐oncological specialties. The present “white paper” catalogs the recommendations of the meeting, at which a consensus was reached that incorporation of molecular information into the next WHO classification should follow a set of provided “ISN‐Haarlem” guidelines. Salient recommendations include that (i) diagnostic entities should be defined as narrowly as possible to optimize interobserver reproducibility, clinicopathological predictions and therapeutic planning; (ii) diagnoses should be “layered” with histologic classification, WHO grade and molecular information listed below an “integrated diagnosis”; (iii) determinations should be made for each tumor entity as to whether molecular information is required, suggested or not needed for its definition; (iv) some pediatric entities should be separated from their adult counterparts; (v) input for guiding decisions regarding tumor classification should be solicited from experts in complementary disciplines of neuro‐oncology; and (iv) entity‐specific molecular testing and reporting formats should be followed in diagnostic reports. It is hoped that these guidelines will facilitate the forthcoming update of the fourth edition of the WHO classification of central nervous system tumors.

Comparative Study of p53 Gene and Protein Alterations in Human Astrocytic Tumors

The p53 gene is a tumor suppressor gene involved in many common malignancies, including astrocytomas. Genetic analysis of the p53 gene and immunohistochemistry of the p53 protein have each been used to screen astrocytomas. To compare these methods, we performed immunohistochemistry with the monoclonal antibody PAb 1801 and single-strand conformational polymorphism (SSCP) with sequence analysis on 34 astrocytic tumors (WHO grades II, III and IV). Seven cases had detectable p53 protein and gene mutations, while twelve cases had neither detectable protein nor gene mutations. Four tumors had frameshift mutations in the p53 gene that were not revealed by immunohistochemistry. One tumor had a genetic polymorphism and no detectable p53 protein. Ten tumors had p53 protein accumulation but no mutations by SSCP; these cases may represent p53 mutations outside of the conserved exons or elevated levels of wild-type p53 protein. Thus, some p53 mutations are missed with PAb 1801 immunohistochemistry alone. p53 immunohistochemistry, however, may reveal p53 accumulation independent of mutations in the conserved portions of the gene. Finally, we suggest that glioblastomas with p53 mutations in the conserved region of the gene may be a subset that are more common in women and in younger patients.

Primitive neuroectodermal tumors after prophylactic central nervous system irradiation in children : association with an activated K-ras gene

Three patients had supratentorial malignant brain tumors 7 to 9 years after prophylactic central nervous system (CNS) treatment for acute lymphocytic leukemia or malignant T‐cell lymphoma. Therapy was administered at the age of 3 to 8 years and included cranial irradiation (total dose, 1800 to 2400 cGy) and intrathecal methotrexate. The brain tumors had histologic and immunohisto chemical features of primitive neuroectodermal tumors (PNET), including neuroblastic rosettes, rhythmic arrangement of tumor cells, and immunohistochemical expression of glial, and in one patient neuronal, marker proteins. Using polymerase chain reaction‐mediated DNA amplification from paraffin‐embedded tissues and subsequent DNA sequence analysis, an activating point mutation was detected in the K‐ras protooncogene in one tumor. This mutation was a G to A transition in position 2 of codon 12, substituting aspartate (GAT) for glycine (GGT). This type of mutation has not been observed before in human brain tumors, but it is frequent in radiation‐induced murine lymphomas. These observations suggest that PNET can be induced after completion of the embryonal and fetal development of the human CNS. On‐cogene‐activating point mutations may represent a pathogenetic mechanism involved in the genesis of radiation‐induced brain tumors.

Type and frequency of p53 mutations in tumors of the nervous system and its coverings.

The p53 tumor suppressor gene encodes a nuclear phosphoprotein which is involved in the regulation of cell proliferation (Boyd and Barrett 1990). The wild-type p53 gene acts as a tumor suppressor gene, whereas some p53 mutations occurring within highly conserved regions not only cause loss of tumor suppressor function but may activate p53 to an oncogene in a dominant negative fashion (Finlay et al. 1989; Eiyahu et al. 1989). A variety of human tumors have been shown to contain either a loss of both alleles of the p53 gene, a loss of one allele of the p53 gene, and one p53 allele with an associated point mutation, insertion, or deletion of the remaining allele or an inactivation of the p53 gene in one allele but a normal (wild-type) sequence in the other. The rapidly accumulating data on p53 genetic alterations indicate that it may constitute the gene most frequently involved in human oncogenesis (Hollstein et al. 1991; Levine et al. 1991). In this review, we summarize all the available data on p53 mutations in human nervous system tumors.

DNA methylation in the digestive tract of F344 rats during chronic exposure toN-methyl-N-nitrosourea

SummaryThe formation ofO6-methyldeoxyguanosine (O6-MedGuo) was determined by an immuno-slot-blot assay in DNA of various tissues of F344 rats exposed toN-methyl-N-nitrosourea (MNU) in the drinking water at 400 ppm for 2 weeks. Although the pyloric region of the glandular stomach is a target organ under these experimental conditions, the extent of DNA methylation was highest in the forestomach (185 μmolO6-MedGuo/mol guanine). Fundus (91 μmol/mol guanine) and pylorus (105 μmol/mol guanine) of the glandular stomach, oesophagus (124 μmol/mol guanine) and duodenum (109 μmol/mol guanine) showed lower levels ofO6-MedGuo but differed little between each other. Thus, no correlation was observed between target organ specificity and the extent of DNA methylation. This is in contrast to the gastric carcinogen,N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), which preferentially alkylates DNA of the pylorus, the main site of induction of gastric carcinomas by this chemical. In contrast to MNU, the non-enzymic decomposition of MNNG is accelerated by thiol compounds (reduced glutathione,l-cysteine), which are present at much higher concentrations in the glandular stomach than in the forestomach and oesophagus. During chronic exposure to MNNG (80 ppm), mucosal cells immunoreactive toO6-MedGuo are limited to the luminal surface [Kobori et al. (1988) Carcinogenesis 9:2271–2274]. Although MNU (400 ppm) produced similar levels ofO6-MedGuo in the pylorus, no cells containing methylpurines were detectable by immunohistochemistry, suggesting a more uniform methylation of mucosal cells by MNU than by MNNG. After a single oral dose of MNU (90 mg/kg) cells containing methylpurines were unequivocally identified using antibodies toO6-MedGuo and the imidazole-ring-opened product of 7-methyldeoxyguanosine. In the gastric fundus, their distribution was similar to those methylated by exposure to MNNG, whereas the pyloric region contained immunoreactive cells also in the deeper mucosal layers. After a 2-week MNU treatment, the rate of cell proliferation, as determined by bromodeoxyuridine immunoreactivity, was only slightly enhanced in the oesophagus and in the fundus, but markedly in the forestomach and the pyloric region of the glandular stomach. It is concluded that the overall extent of DNA methylation, the distribution of alkylated cells within the mucosa and the proliferative response all contribute to the organ-specific carcinogenicity of MNU.