Germline mutations of the PTEN gene in Cowden disease, an inherited breast and thyroid cancer syndrome

Genotypic analysis of tumor suppressor genes PTEN/MMAC1 and p53 in head and neck squamous cell carcinomas

OBJECTIVES

Tumor suppressor gene mutations in both p53 and PTEN/MMAC1 genomic DNA have been detected in many types of cancer. The purpose of this study was to investigate the presence and importance of PTEN/MMAC1 mutations in squamous cell carcinomas.

METHODS

Exons of each gene were amplified after polymerase chain reaction (PCR) using genomic DNA derived from cell lines of squamous cell carcinoma of the head and neck (SCCHN) and snap-frozen biopsy specimens from primary established head and neck tumors. The amplified and purified DNA was then sequenced directly.

RESULT

As anticipated, point mutations of the p53 gene were found in 80% of cell lines examined. A single base mutation in codon 151 was found in six of 10 cell lines studied. PTEN/MMAC1 gene mutations were found in neither the cell lines tested nor the tumor biopsy samples.

CONCLUSION

This study, as well as a large volume of data, confirms that mutations of the p53 gene are frequent events in head and neck cancer cell lines. Although PTEN/MMAC1 gene mutations have been found in a variety of carcinomas, this gene was not found to be mutated in SCCHN cell lines or in primary squamous cell carcinomas of the head and neck. This information is useful for further studies of mutations in these cell lines.

Mutational analysis of the PTEN gene in head and neck squamous cell carcinoma

Loss of heterozygosity (LOH) at chromosome band 10q23 occurs frequently in a wide variety of human tumors. A recently identified candidate tumor suppressor gene, PTEN located on 10q23, is mutated in multiple advanced cancers. To explore whether PTEN is associated with human squamous cell carcinoma of the head and neck (SCCHN), DNAs from both normal muscle and tumor tissue in 19 SCCHN were used for detecting LOH at chromosome 10q23 and mutational analysis of PTEN by direct polymerase chain reaction (PCR)-DNA sequencing. LOH at 10q23 was identified in 6/15 SCCHN. Mutation of PTEN was identified in 3/19 SCCHN. Of these 3 patients, 2 had stage IV disease; the third patient, with recurrent, metastatic and stage III disease, showed a 36 bp germline heterozygous deletion within intron 7. Furthermore, a missense mutation at codon 501 (TCT --> TTT: Ser --> Phe) in exon 8 was also found in tumor from the same patient. Our results suggest that PTEN may play a role in the genesis of some SCCHNs.

In vitro loss of heterozygosity targets the PTEN/MMAC1 gene in melanoma

Gross genetic lesions of chromosome 10 occur in 30-50% of sporadic human melanomas. To test the functional significance of this observation, we have developed an in vitro loss of heterozygosity approach in which a wild-type chromosome 10 was transferred into melanoma cells, where there was selection for its breakage and regional deletion to relieve its growth suppressive effects. The overlap of these events was at band 10q23, the site of the recently isolated PTEN/MMAC1 tumor suppressor gene, suggesting it as a potential target. Although the gene was expressed in the parental cells, both of its chromosomal alleles contained truncating mutations. In vitro loss of heterozygosity resulted in loss of the chromosomally introduced wild-type PTEN/MMAC1, and ectopic expression of the gene caused cell growth suppression. Thus, this approach identified PTEN/MMAC1 as a target in malignant melanoma and may provide an alternative means to localizing tumor suppressor genes.

Pten is essential for embryonic development and tumour suppression

The PTEN gene encodes a dual-specificity phosphatase mutated in a variety of human cancers. PTEN germline mutations are found in three related human autosomal dominant disorders, Cowden disease (CD), Lhermitte-Duclos disease (LDD) and Bannayan-Zonana syndrome (BZS), characterized by tumour susceptibility and developmental defects. To examine the role of PTEN in ontogenesis and tumour suppression, we disrupted mouse Pten by homologous recombination. Pten inactivation resulted in early embryonic lethality. Pten-/- ES cells formed aberrant embryoid bodies and displayed an altered ability to differentiate into endodermal, ectodermal and mesodermal derivatives. Pten+/- mice and chimaeric mice derived from Pten+/- ES cells showed hyperplastic-dysplastic changes in the prostate, skin and colon, which are characteristic of CD, LDD and BZS. They also spontaneously developed germ cell, gonadostromal, thyroid and colon tumours. In addition, Pten inactivation enhanced the ability of ES cells to generate tumours in nude and syngeneic mice, due to increased anchorage-independent growth and aberrant differentiation. These results support the notion that PTEN haploinsufficiency plays a causal role in CD, LDD and BZS pathogenesis, and demonstrate that Pten is a tumour suppressor essential for embryonic development.

Genetic pathways of colorectal carcinogenesis rarely involve the PTEN and LKB1 genes outside the inherited hamartoma syndromes

Germline mutations of the PTEN/MMAC1/TEP and LKB1 genes cause hamartomas to develop in the gastrointestinal tracts of patients with Cowden syndrome and Peutz-Jeghers syndrome, respectively. PTEN mutations may also be responsible for some cases of juvenile polyposis. Histologically, hamartomas appear benign, but there is good evidence that in these syndromes, the hamartomas can progress to colorectal carcinoma. It remains unknown whether or not cancers that develop from hamartomas acquire a spectrum of mutations similar to those in sporadic colon cancers. PTEN and LKB1 are candidate genes for mutations in sporadic colon cancers, either as initiating events in tumorigenesis or providing a selective advantage during tumor growth. Using single-strand conformational polymorphism analysis, we have screened a set of sporadic colon cancers for somatic mutations in PTEN and LKB1. No variants predicted to alter protein function were detected in LKB1, but 1 of 72 cancers showed a somatic mutation in PTEN, together with allele loss. This cancer did not have a detectable APC mutation or allele loss at APC. It remains possible that PTEN and LKB1 are inactivated in other sporadic colon cancers by means such as deletion or promoter methylation. Like BRCA1 and BRCA2, however, it appears that PTEN and LKB1 mutations can cause cancers when present in the germline, but occur rarely in the soma.

Somatic mutations of the PTEN/MMAC1 gene in fifteen Japanese endometrial cancers: evidence for inactivation of both alleles

Loss of heterozygosity (LOH) of chromosome 10q is observed in approximately 40% of endometrial cancers. Mutations in PTEN/MMAC1, a gene recently isolated from the 10q23 region, are responsible for two dominantly inherited neoplastic syndromes, Cowden disease and Bannayan-Zonana syndrome. Somatic mutations of this gene have also been detected in sporadic cancers of the brain, prostate and breast. To investigate the potential role of this putative tumor suppressor gene in endometrial carcinogenesis as well, we examined 46 primary endometrial cancers for LOH at the 10q23 region, and for mutations in the entire coding region and exon-intron boundaries of the PTEN/MMAC1 gene. LOH was identified in half of the 38 informative cases, and subtle somatic mutations were detected in 15 tumors (33%). Our results suggest that of the genes studied so far in endometrial carcinomas, PTEN/MMAC1 is the most commonly mutated one, and that inactivation of both copies by allelic loss and/or mutation, a pattern that defines genes as "tumor suppressors," contributes to tumorigenesis in endometrial cancers.

Carney complex, Peutz-Jeghers syndrome, Cowden disease, and Bannayan-Zonana syndrome share cutaneous and endocrine manifestations, but not genetic loci

Carney complex (CC), Peutz-Jeghers syndrome (PJS), Cowden disease (CD), and Bannayan-Zonana syndrome (BZS) share clinical features, such as mucocutaneous lentigines and multiple tumors (thyroid, breast, ovarian, and testicular neoplasms), and autosomal dominant inheritance. A genetic locus has been identified for CC on chromosome 2 (2p16), and the genes for PJS, CD, and BZS were recently identified; genetic heterogeneity appears likely in both CC and PJS. The genes for PJS and CD/BZS, STK11/LKB1 and PTEN, respectively, may act as tumor suppressors, because loss of heterozygosity (LOH) of the PJS and CD/BZS loci has been demonstrated in tumors excised from patients with these disorders. We studied 2 families with CC in whom the disease could not be shown to segregate with polymorphic markers from the 2p16 locus. Their members presented with lesions frequently seen in PJS and the other lentiginosis syndromes. We also tested 16 tumors and cell lines established from patients with CC for LOH involving the PJS and CD/BZS loci. DNA was extracted from peripheral blood, tumor cell lines, and tissues and subjected to PCR amplification with primers from microsatellite sequences flanking the STK11/LKB1 and PTEN genes on 19p13 and 10q23, respectively, and a putative PJS locus on 19q13. All loci were excluded as candidates in both families with LOD scores less than 2 and/or by haplotype analysis. LOH for these loci was not present in any of the tumors that were histologically identical to those seen in PJS. The overall rate of LOH for the PJS and CD/BZS loci in tumors from patients with CC was less than 10%. We conclude that despite substantial clinical overlap among CC, PJS, CD, and BZS, LOH for the STK11 and PTEN loci is an infrequent event in CC-related tumors. Linkage analysis excluded the PJS and CD/BZS loci on chromosomes 19 (19p13 and 19q13) and 10 (10q23) from harboring the gene defect(s) responsible for the phenotype in these 2 families.

Bannayan-Zonana syndrome: a rare autosomal dominant syndrome with multiple lipomas and hemangiomas: a case report and review of literature

BACKGROUND

Bannayan-Zonana syndrome is a rare hamartomatous disorder, characterized by macrocephaly, multiple lipomas, and hemangiomas. Inheritance is by autosomal dominant transmission with few reported sporadic cases. Male predominance is also reported.

METHODS

We describe a patient who presented with multiple subcutaneous lipomas, mild macrocephaly, and an extradural spinal hemangioma. Other affected family members and 24 other previously reported cases are discussed.

RESULTS

Spinal hemangiomas have not been described previously with this syndrome. The patient also had a "malignant bone tumor" removed from his humerus 20 years ago. Two of the patient's siblings also had lymphoma, which is an unusual accompaniment not reported previously. Only the male members in the family showed multiple subcutaneous lipomas.

CONCLUSION

Some patients with Bannayan-Zonana syndrome may have hamartomatous lesions producing cord compression or intracerebral hemorrhage, or they may rarely have other malignant tumors; therefore it is important that neurosurgeons are aware of the entity. The early diagnosis of BZS is also important for genetic counseling.

Mutation of the PTEN tumor suppressor gene is not a feature of ovarian cancers

OBJECTIVE

The PTEN tumor suppressor gene on chromosome 10q23 undergoes inactivating mutations in several types of malignancies including glioblastomas and prostate and endometrial carcinomas. The aim of this study was to determine if mutation of the PTEN tumor suppressor gene is a feature of sporadic or BRCA1-associated ovarian carcinomas.

METHODS

Genomic deoxyribonucleic acid was extracted from 11 ovarian cancer cell lines and 50 frozen ovarian cancers, including 4 cases that developed in women with germline mutations in the BRCA1 breast/ovarian cancer susceptibility gene. The polymerase chain reaction was used to amplify each of the nine exons and intronic splice sites of the PTEN gene. These products were then screened for mutations using single strand conformation polymorphism analysis. Variant bands were further evaluated using automated DNA sequencing.

RESULTS

A previously unreported silent polymorphism at codon 240 (TAT to TAC) in exon 7 was noted in one of the primary ovarian carcinomas. Mutations in the PTEN gene were not found in any of the 50 primary ovarian cancers or 11 immortalized ovarian cancer cell lines.

CONCLUSION

Alteration of the PTEN tumor suppressor gene does not appear to be a feature of sporadic or BRCA1-associated ovarian cancers.

Inactivation of the PTEN/MMAC1/TEP1 gene in human lung cancers

The PTEN/MMAC1/TEP1 gene has been isolated as a tumor suppressor gene that is altered in several types of human tumors including brain, breast, and prostate cancers. In the present study, we report PTEN/MMAC1/TEP1 alterations in human lung cancers. Intragenic homozygous deletions were detected in 6 (40%) of 15 small cell lung carcinoma (SCLC) cell lines and in 2 (8%) of 25 non-small cell lung carcinoma (NSCLC) cell lines. A nonsense mutation and a missense mutation were detected in 2 (8%) NSCLC cell lines. An intragenic homozygous deletion, a 1-bp frameshift mutation, and a nonsense somatic mutation were also detected in three (6%) of 47 surgical specimens. All the lung tumors with PTEN/MMAC1/TEP1 mutations were homozygous for the mutant alleles. These findings suggest that PTEN/MMAC1/TEP1 plays a role as a tumor suppressor gene in the genesis and/or progression of human lung cancer.

A review of tumor suppressor genes in cutaneous neoplasms with emphasis on cell cycle regulators

Cells normally have five options. These include renewal or proliferation, terminal differentiation, quiescence, senescence, and apoptosis. Many factors interact with cell cycle regulators to direct the cells toward these different options. Tumor suppressor genes play a pivotal role in this process. Alterations in these genes may limit the options that cells have and thus play a significant role in the multistep process of carcinogenesis. We will focus on tumor suppressor genes and especially tumor suppressor genes that interact directly with the cell cycle proteins.

A survey of phenotypic features in juvenile polyposis

Solitary juvenile polyps are quite frequent in children, but juvenile polyposis (JP) is a rare autosomal dominant trait characterised by the occurrence of numerous polyps in the gastrointestinal tract. Extracolonic phenotypic abnormalities are well documented in patients with familial adenomatous polyposis and Peutz-Jeghers syndrome and can allow a clinical diagnosis to be made before the bowel pathology becomes available. Though described, characteristic extracolonic abnormalities have not been clearly defined in juvenile polyposis. We sought to determine whether there are consistent extracolonic phenotypic abnormalities in JP patients and how frequently this would allow diagnosis of one of the genetic syndromes known to be associated with juvenile polyposis. Twenty-two JP patients underwent clinical examination and data from one patient were obtained from case notes. Those consenting to further investigations had x rays of the skull, chest, and hands and an echocardiogram if clinically indicated. Significant extracolonic phenotypic abnormalities were present in 18 patients (14 male and four female), and included dermatological (13), skeletal (16), neurological (5), cardiopulmonary (4), gastrointestinal (3), genitourinary (4), and ocular (1) features. In five patients the diagnosis of a genetic syndrome was possible: two had Bannayan-Riley-Ruvalcaba syndrome, two had Gorlin syndrome, and one had hereditary haemorrhagic telangiectasia (HHT, also known as Osler-Rendu-Weber syndrome). Other patients had some features of these conditions and of Cowden and Simpson-Golabi-Behmel syndromes, but these were not sufficient to allow a definitive diagnosis.

Mutations in the SMAD4/DPC4 gene in juvenile polyposis

Familial juvenile polyposis is an autosomal dominant disease characterized by a predisposition to hamartomatous polyps and gastrointestinal cancer. Here it is shown that a subset of juvenile polyposis families carry germ line mutations in the gene SMAD4 (also known as DPC4), located on chromosome 18q21.1, that encodes a critical cytoplasmic mediator in the transforming growth factor-beta signaling pathway. The mutant SMAD4 proteins are predicted to be truncated at the carboxyl-terminus and lack sequences required for normal function. These results confirm an important role for SMAD4 in the development of gastrointestinal tumors.

A gene for familial juvenile polyposis maps to chromosome 18q21.1

Familial juvenile polyposis (FJP) is a hamartomatouspolyposis syndrome in which affected family members develop upper and lower gastrointestinal juvenile polyps and are at increased risk for gastrointestinal cancer. A genetic locus for FJP has not yet been identified by linkage; therefore, the objective of this study was to perform a focused genome screen in a large family segregating FJP. No evidence for linkage was found with markers near MSH2, MLH1, MCC, APC, HMPS, CDKN2A, JP1, PTEN, KRAS2, TP53, or LKB1. Linkage to FJP was established with several markers from chromosome 18q21.1. The maximum LOD score was 5.00, with marker D18S1099 (recombination fraction of .001). Analysis of critical recombinants places the FJP gene in an 11.9-cM interval bounded by D18S1118 and D18S487, a region that also contains the tumor-suppressor genes DCC and DPC4. These data demonstrate localization of a gene for FJP to chromosome 18q21.1 by linkage, and they raise the possibility that either DCC or DPC4 could be responsible for FJP.

Germline mutations of the PTEN/MMAC1 gene in Japanese patients with Cowden disease

Cowden disease (CD) is an autosomal dominant disorder which confers a high susceptibility to diverse benign and malignant tumors. The PTEN/MMAC1 gene was identified as being responsible for CD, since its germline mutations have been identified in affected individuals in the United States and Europe. We identified three novel germline PTEN mutations, a 2-bp deletion, a 1-bp insertion and a missense mutation, in three of five Japanese patients with CD. The missense mutation resided outside of the region encoding a putative phosphatase domain of the predicted PTEN protein, where previously reported missense mutations in CD patients have been clustered. The present result suggests that a wide range of germline PTEN mutations may play a role in the pathogenesis of CD.

The Croonian Lecture 1997. The phosphorylation of proteins on tyrosine: its role in cell growth and disease

The reversible phosphorylation of tyrosines in proteins plays a key role in regulating many different processes in eukaryotic organisms, such as growth control, cell cycle control, differentiation cell shape and movement, gene transcription, synaptic transmission, and insulin action. Phosphorylation of proteins is brought about by enzymes called protein-tyrosine kinases that add phosphate to specific tyrosines in target proteins; phosphate is removed from phosphorylated tyrosines by enzymes called protein-tyrosine phosphatases. Phosphorylated tyrosines are recognized by specialized binding domains on other proteins, and such interactions are used to initiate intracellular signaling pathways. Currently, more than 95 protein-tyrosine kinases and more than 55 protein-tyrosine phosphatase genes are known in Homo sapiens. Aberrant tyrosine phosphorylation is a hallmark of many types of cancer and other human diseases. Drugs are being developed that antagonize the responsible protein-tyrosine kinases and phosphatases in order to combat these diseases.

Inactivation of the tumor suppressor PTEN/MMAC1 in advanced human prostate cancer through loss of expression

The recently identified PTEN/MMAC1 gene is a candidate tumor suppressor implicated in multiple tumor types based on mutations or homozygous deletions of the gene in certain human cancers. No studies of PTEN/MMAC1 mRNA or protein expression in cancer cells have been reported, primarily because of significant numbers of normal cells contaminating most tumor samples and because of the lack of antibody reagents. We examined PTEN/MMAC1 in advanced prostate cancer for gene mutations or abnormalities in expression by using a series of recently derived xenografts free of normal human cells and a PTEN/MMAC1-specific antibody. Only 1 of 10 tumors contained a homozygous deletion of PTEN/MMAC1, and no mutations were detected in the entire coding region of the remaining nine xenografts. However, five of these showed reduced or absent PTEN/MMAC1 expression by Northern analysis and reverse transcription-PCR of mRNA. PTEN/MMAC1 mRNA expression was restored in nonexpressing prostate cancer cells by in vitro treatment with the demethylating agent 5-azadeoxycytidine. Alterations in PTEN/MMAC1 expression were confirmed at the protein level by immunoblot analysis, and immunohistochemical studies show that the endogenous wild-type PTEN/MMAC1 protein is localized exclusively in the cytoplasm. These results demonstrate that loss of PTEN/MMAC1 expression occurs frequently in advanced prostate cancer.

Protein-tyrosine phosphatases: biological function, structural characteristics, and mechanism of catalysis

The protein-tyrosine phosphatases (PTPases) superfamily consists of tyrosine-specific phosphatases, dual specificity phosphatases, and the low-molecular-weight phosphatases. They are modulators of signal transduction pathways that regulate numerous cell functions. Malfunction of PTPases have been linked to a number of oncogenic and metabolic disease states, and PTPases are also employed by microbes and viruses for pathogenicity. There is little sequence similarity among the three subfamilies of phosphatases. Yet, three-dimensional structural data show that they share similar conserved structural elements, namely, the phosphate-binding loop encompassing the PTPase signature motif (H/V)C(X)5R(S/T) and an essential general acid/base Asp residue on a surface loop. Biochemical experiments demonstrate that phosphatases in the PTPase superfamily utilize a common mechanism for catalysis going through a covalent thiophosphate intermediate that involves the nucleophilic Cys residue in the PTPase signature motif. The transition states for phosphoenzyme intermediate formation and hydrolysis are dissociative in nature and are similar to those of the solution phosphate monoester reactions. One strategy used by these phosphatases for transition state stabilization is to neutralize the developing negative charge in the leaving group. A conformational change that is restricted to the movement of a flexible loop occurs during the catalytic cycle of the PTPases. However, the relationship between loop dynamics and enzyme catalysis remains to be established. The nature and identity of the rate-limiting step in the PTPase catalyzed reaction requires further investigation and may be dependent on the specific experimental conditions such as temperature, pH, buffer, and substrate used. In-depth kinetic and structural analysis of a representative number of phosphatases from each group of the PTPase superfamily will most likely continue to yield insightful mechanistic information that may be applicable to the rest of the family members.

Association of SET domain and myotubularin-related proteins modulates growth control

Several proteins that contribute to epigenetic mechanisms of gene regulation contain a characteristic motif of unknown function called the SET (Suvar3-9, Enhancer-of-zeste, Trithorax) domain. We have demonstrated that SET domains mediate highly conserved interactions with a specific family of proteins that display similarity with dual-specificity phosphatases (dsPTPases). These include myotubularin, the gene of which is mutated in a subset of patients with X-linked myotubular myopathy, and Sbf1, a newly isolated homologue of myotubularin. In contrast with myotubularin, Sbf1 lacks a functional catalytic domain which dephosphorylates phospho-tyrosine and serine-containing peptides in vitro. Competitive interference of endogenous SET domain-dsPTPase interactions by forced expression of Sbf1 induced oncogenic transformation of NIH 3T3 fibroblasts and impaired the in vitro differentiation of C2 myoblast cells. We conclude that myotubularin-type phosphatases link SET-domain containing components of the epigenetic regulatory machinery with signalling pathways involved in growth and differentiation.

Breast cancer genes and the surgeon

Two genes, called BRCA-1 and BRCA-2, have been identified that appear to be responsible for the majority of familial breast cancer syndromes. These genes now play a prominent role in the practice of the surgeon treating breast cancer. Additional genes, PTEN (Cowden disease), MSH1 or MLH2 (HNPCC), and p53 (Li-Fraumeni syndrome) are responsible for other breast cancer syndromes but have not yet entered the clinical arena on a large scale. The risk of breast and ovarian cancer by age 70 in a BRCA-1 mutation carrier is estimated at 55-75% and 16-26 %, respectively, overall, and as high as 87% and 44% in those with a strong family history. The cancer risks associated with BRCA-2 mutations appear to be somewhat lower than those of BRCA-1. BRCA mutations show a strong founder effect. This is best recognized in the Ashkenazi Jewish community, in which the incidence of one of three characteristic mutations is about 2%. In other ethnic groups the pattern of mutations is different, with over 100 distinct mutations throughout the genes having been described. Most mutations so far have been frame-shift or mis-sense mutations, although large deletions have also been described. Thus, in most situations, assessment of the whole coding sequence is required to confirm or exclude a mutation. Guidelines to suggest who is likely to be a mutation carrier are being clarified, but the appropriate management of someone who tests positive remains difficult. Prophylactic mastectomy and oophorectomy are likely to offer substantial gains in life expectancy to mutation carriers, especially for young women with a strong family history. Unfortunately, there are no currently available strategies to eliminate the risk of breast or ovarian cancer. The psychological impact of testing also remains poorly understood, and the danger of various forms of discrimination remain. These factors must be clearly understood by all parties prior to testing. The process of a dynamic, interactive informed consent--much more than a simple printed document--and also counseling are central to the testing process.

Investigation of genetic alterations associated with the grade of astrocytic tumor by comparative genomic hybridization

Comparative genomic hybridization (CGH) is a technique that allows the detection of losses and gains in DNA copy number across the entire genome. We used CGH to study the genetic alterations that occur in primary astrocytomas, including 14 glioblastomas (GBM), 12 anaplastic astrocytomas (AA), and 7 low-grade astrocytomas (LGA). The average numbers of total aberrations in GBM, AA, and LGA were 9.7, 5.4, and 4.0, respectively. The average number of DNA sequence losses in GBM was significantly higher than that in AA or LGA (P < 0.01). Frequently altered regions (> eight cases) observed in all grades of astrocytoma were 7p13-p12 (gain), 7q31 (gain), 8q24.1-q24.2 (gain), 9p21 (loss), 10p12-p11 (loss), 10q22-qter (loss), 13q21-q22 (loss), and 20q13.1-q13.2 (gain). Loss of 9p, 10p, or 10q, and the gain or amplification of 7p, were observed frequently in GBM (64%, 57%, 64%, and 50% of cases, respectively). Frequent alterations found in AA were losses of 9p, 10q, and 13q, and gains of 1q, chromosome 7, 11q, and Xq. Whereas 7p13-p11 amplification occurred exclusively in cases with the loss of all or part of chromosome 10, this change never occurred in cases having an increase in copy number of 8q, which was the most frequent change observed in LGA (four of seven cases). These results may indicate that an increase in copy number of 8q is an important event in GBM, with a genetic pathway, which is distinct from that in GBM with 7p amplification.

Cancer predisposition: where's the phosphate?

Mutations in a protein phosphatase and a protein kinase cause hamartomatous polyposis syndromes, which are characterised by the formation of multiple benign polyps and an increased susceptibility to some types of cancer.

Hereditary breast cancer

Genetic predisposition is responsible for 5-10% of all breast cancer, and a much larger percent of early-onset disease. Within the past few years, a number of genes associated with a high risk of breast cancer have been identified, including BRCA1, BRCA2, p53, and the Cowden disease gene PTEN/MMAC1. These genes appear to function as tumor suppressors, and although their mutation frequency in the general population is low, certain populations have a carrier frequency of up to 1% for particular BRCA1 and BRCA2 mutations. The isolation of these genes is likely to provide important insight into the pathogenesis of human cancer. The clinical application of these molecular discoveries raises controversial issues regarding presymptomatic testing for patients suspected of harboring cancer predisposing mutations.

Genetic heterogeneity and penetrance analysis of the BRCA1 and BRCA2 genes in breast cancer families. The Breast Cancer Linkage Consortium

The contribution of BRCA1 and BRCA2 to inherited breast cancer was assessed by linkage and mutation analysis in 237 families, each with at least four cases of breast cancer, collected by the Breast Cancer Linkage Consortium. Families were included without regard to the occurrence of ovarian or other cancers. Overall, disease was linked to BRCA1 in an estimated 52% of families, to BRCA2 in 32% of families, and to neither gene in 16% (95% confidence interval [CI] 6%-28%), suggesting other predisposition genes. The majority (81%) of the breast-ovarian cancer families were due to BRCA1, with most others (14%) due to BRCA2. Conversely, the majority of families with male and female breast cancer were due to BRCA2 (76%). The largest proportion (67%) of families due to other genes was found in families with four or five cases of female breast cancer only. These estimates were not substantially affected either by changing the assumed penetrance model for BRCA1 or by including or excluding BRCA1 mutation data. Among those families with disease due to BRCA1 that were tested by one of the standard screening methods, mutations were detected in the coding sequence or splice sites in an estimated 63% (95% CI 51%-77%). The estimated sensitivity was identical for direct sequencing and other techniques. The penetrance of BRCA2 was estimated by maximizing the LOD score in BRCA2-mutation families, over all possible penetrance functions. The estimated cumulative risk of breast cancer reached 28% (95% CI 9%-44%) by age 50 years and 84% (95% CI 43%-95%) by age 70 years. The corresponding ovarian cancer risks were 0.4% (95% CI 0%-1%) by age 50 years and 27% (95% CI 0%-47%) by age 70 years. The lifetime risk of breast cancer appears similar to the risk in BRCA1 carriers, but there was some suggestion of a lower risk in BRCA2 carriers <50 years of age.

The molecular genetics of endocrine tumours

The molecular genetics of endocrine tumours is an area of great interest, due to the heterogeneity of endocrine tumour types, the association of hormone over-production in some cases, and the wide variation in tumour behaviour. Genes implicated fall into functional categories such as oncogenes, in which mutations tend to cause activation, and tumour suppressor genes, in which mutations lead to loss of function. Oncogenes include the receptor tyrosine kinases such as RET, signal transduction proteins and other molecules such as cell cycle regulators and nuclear proteins. Tumour suppressor genes include cell cycle regulators such as p53 and other molecules such as the MEN 1 gene. Loss of heterozygosity studies help in the initial localisation of the latter. Endocrine tumours, as with other tumours, develop as a result of a combination of genetic events, and in the paediatric age group they often occur in the setting of familial cancer syndromes. In this review we analyse the main genetic lesions which have been described in endocrine tumours. There has been an explosion of knowledge in the last 5 years including the identification of the causative genes for MEN 2 and most recently for MEN 1. Characterisation of such genes also aids in the study of somatic mutations in sporadic versions of the same tumour types as occur in the familial syndromes. Identification of a genetic predisposition to a certain tumour has management implications that are still to be clarified in most cases, although in the case of MEN 2 the guidelines for prophylactic thyroidectomy are generally well accepted.

Analysis of the PTEN gene in human meningiomas

Previous observations demonstrated that the neurofibromatosis type 2 gene (NF2) plays an important role in the pathogenesis of the transitional, fibroblastic and malignant variants of human meningiomas. No specific genes have been associated with the pathogenesis of meningothelial meningiomas and with the progression to anaplastic meningiomas. However, allelic losses on chromosomal arms 1p, 10q and 14q have been implicated in the process of malignant progression. Recently, PTEN (phosphatase and tensin homolog deleted on chromosome ten) also termed MMAC1 (mutated in multiple advanced cancers 1) or TEP1 (TGF--regulated and epithelial cell-enriched phosphatase), emerged as a candidate gene on chromosome 10q23.3. Initial studies revealed mutations of PTEN in limited series of glioblastomas, breast, kidney and prostate carcinomas mainly as cell lines. In order to evaluate the involvement of PTEN in the development of meningiomas, we have analysed the entire coding sequence of the gene in a series of 55 meningiomas (WHO grade I). 10 atypical meningiomas (WHO grade II) and 10 anaplastic meningiomas (WHO grade III). No PTEN mutations were seen in the WHO grade I meningiomas. However, one of the anaplastic meningiomas carried a somatic mutation. In addition, all tumours were examined for the presence of homozygous deletions of PTEN but these were not detected in any of the meningiomas. Our data suggest that mutations in PTEN are not involved in the formation of low grade meningiomas, but may contribute to malignant progression in a fraction of anaplastic meningiomas.

Inherited susceptibility to breast and ovarian cancer

Approximately 5-10% of breast and ovarian cancer cases are due to an inherited susceptibility. The majority of inherited breast and ovarian cancer susceptibility is due to mutations in the BRCA1 and BRCA2 genes; however, other genes responsible for inherited susceptibility to these diseases are yet to be identified. A small proportion of inherited breast and ovarian cancers are due to other genetic cancer susceptibility syndromes including Li-Fraumeni syndrome, Cowden disease and hereditary non-polyposis colorectal cancer. It is recommended that individuals at risk for inherited susceptibility to breast and/or ovarian cancer who are requesting DNA testing be provided with pre-test genetic counseling and education and post-test counseling and follow-up to ensure that all aspects of genetic testing have been disclosed and that the patient has truly given informed consent.

Deletion 10q23.2-q23.33 in a patient with gastrointestinal juvenile polyposis and other features of a Cowden-like syndrome

A cytogenetically visible interstitial deletion of chromosome band 10q23 was found in a 6-year-old boy with mental retardation, dysmorphic features, and juvenile polyposis coli. In order to map this patient's deletion physically, we performed fluorescence in situ hybridization by using yeast artificial chromosomes (YACs) in the vicinity of the deletion. Five YACs that span an 11-15 cM region within the deletion were identified. This patient's deletion contains the putative locus for Cowden syndrome and a recently discovered candidate tumor suppressor gene (MMAC1 or PTEN) that has been implicated in the progression of a variety of human malignancies. Furthermore, the deletion is near and possibly overlaps a locus associated with juvenile polyposis. The findings in this patient with a constitutional 10q23 deletion raise the issue of whether there are separate genes in this region that are involved in Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, juvenile polyposis, and tumor progression, or whether all of these entities could be due to a single gene.

Ductal carcinoma in situ of the breast: histological classification and genetic alterations

Ductal carcinoma in situ (DCIS) of the breast represents a proliferation of malignant epithelial cells within the ducts and lobules of the breast, without invasion through the basement membrane. It is believed that all invasive carcinomas are preceded by DCIS; however, it is not known what proportion of patients with DCIS will develop invasive carcinoma and after what interval. DCIS is heterogeneous with respect to its clinical presentation, mammographic abnormalities, histology and biology. The risk of progression to invasive carcinoma depends on the histologic type of DCIS and the size of the lesion; in the future, the analysis of the genetic alterations may also help in predicting the risk of progression to invasive breast cancer. As the risk of progression to invasive breast cancer (and the development of metastases) greatly influences the choice of treatment for DCIS, it is of importance to be able to make a reliable estimate of this risk of progression. In this chapter, the histologic classification of DCIS and the genetic alterations that have been found to date are discussed.

Peutz-Jeghers syndrome is caused by mutations in a novel serine threonine kinase

Peutz-Jeghers (PJ) syndrome is an autosomal-dominant disorder characterized by melanocytic macules of the lips, multiple gastrointestinal hamartomatous polyps and an increased risk for various neoplasms, including gastrointestinal cancer. The PJ gene was recently mapped to chromosome 19p13.3 by linkage analysis, with the highest lod score at marker D19S886. In a distance of 190 kb proximal to D19S886, we identified and characterized a novel human gene encoding the serine threonine kinase STK11. In a three-generation PJ family, we found an STK11 allele with a deletion of exons 4 and 5 and an inversion of exons 6 and 7 segregating with the disease. Sequence analysis of STK11 exons in four unrelated PJ patients has identified three nonsense and one acceptor splice site mutations. All five germline mutations are predicted to disrupt the function of the kinase domain. We conclude that germline mutations in STK11, probably in conjunction with acquired genetic defects of the second allele in somatic cells, cause the manifestations of PJ syndrome.

Allelic imbalance, including deletion of PTEN/MMACI, at the Cowden disease locus on 10q22-23, in hamartomas from patients with Cowden syndrome and germline PTEN mutation

Cowden disease (CD) is a rare, autosomal dominant inherited cancer syndrome characterized by multiple benign and malignant lesions in a wide spectrum of tissues. While individuals with CD have an increased risk of breast and thyroid neoplasms, the primary features of CD are hamartomas. The gene for CD has been mapped by linkage analysis to a 6 cM region on the long arm of chromosome 10 at 10q22-23. Loss of heterozygosity (LOH) studies of sporadic follicular thyroid adenomas and carcinomas, both component tumors of CD, have suggested that the putative susceptibility gene for CD is a tumor suppressor gene. Somatic missense and nonsense mutations have recently been identified in breast, prostate, and brain tumor cell lines in a gene encoding a dual specificity phosphatase, PTEN/MMACI, mapped at 10q23.3. Furthermore, germline PTEN/MMACI mutations are associated with CD. In the present study, 20 hamartomas from 11 individuals belonging to ten unrelated families with CD have been examined for LOH of markers flanking and within PTEN/MMACI. Eight of these ten families have germline PTEN/MMACI mutations. LOH involving microsatellite markers within the CD interval, and including PTEN/MMACI, was identified in two fibroadenomas of the breast, a thyroid adenoma, and a pulmonary hamartoma belonging to 3 to 11 (27%) of these patients. The wild-type allele was lost in these hamartomas. Semi-quantitative PCR performed on RNA from hamartomas from three different tissues from a CD patient suggested substantial reduction of PTEN/MMACI RNA levels in all of these tissues. The LOH identified in samples from individuals with CD and the suggestion of allelic loss and reduced transcription in hamartomas from a CD patient provide evidence that PTEN/MMACI functions as a tumor suppressor in CD.

Recent advances in the molecular genetics of cancer. Second joint conference of the American Association of Cancer Research and the European Association of Cancer Research, Oxford, 9-12 September 1997

The second joint conference of the AACR and the EACR held in Oxford from 9-12 September 1997 was successful from many vantage points. While providing an optimal setting in which European and American cancer researchers could meet and exchange information, the conference had an excellent scientific programme which encompassed both methodological updates on important models used in cancer research and presentations of recent key advances in the molecular genetics of cancer. Lower eukaryotes are established model organisms used to elucidate fundamental but complex eukaryotic processes, such as those involved in tumorigenesis and cancer progression, and the progressive availability of their genome sequence makes them even more attractive. Transgenic mouse models are increasingly used not only for the study of one gene of interest but for investigation of the interactions among genes involved in the same pathway. The family of tumour suppressor genes is growing fast and several presentations were devoted to recently identified members such as the Von Hippel-Lindau gene, the FHIT gene and the PTEN gene. The systematic analysis of loss of heterozygosity on multiple loci in tumour specimens can provide the basis for preliminary models of molecular multistep progression in some tumour types, even though this is limited by the high degree of complexity found. Mechanisms of cell cycle regulation and apoptosis continue to be dissected and to constitute a fruitful area of investigation, with important recent insights on the p53-MDM2 autoregulatory loop and on the involvement of E2F-1 in apoptosis.

Infrequent mutations in the PTEN/MMAC1 gene among primary breast cancers

Recently PTEN/MMAC1, a candidate tumor suppressor gene, was isolated from chromosome 10q23-24 and somatic mutations of this gene were detected in several malignancies including brain, prostate, and breast tumors. To investigate further the potential role of this gene in mammary carcinogenesis, we examined 69 primary breast cancers for mutations in PTEN/MMAC1 by means of polymerase chain reaction single-strand conformation polymorphism and sequencing analysis. We detected only one somatic missense mutation, a change from T to C at codon 59 (TCA to CCA) resulting in substitution of Pro for Ser in the predicted protein. This site is located outside of phosphatase or phosphate-acceptor motifs, but this codon encodes a residue that is conserved in homologous proteins, tensin and auxilin and is likely to be crucial for normal function of PTEN/MMAC1. Among the 69 tumors examined, three low-frequency polymorphisms were found as well, one in the non-coding region of exon 1 and one each in introns 2 and 7. Our results suggested that mutation of the PTEN/MMAC1 gene is not a major factor in the development of most primary breast cancers.

Peutz-Jeghers disease: most, but not all, families are compatible with linkage to 19p13.3

A locus for Peutz-Jeghers syndrome (PJS) was recently mapped to chromosome 19p13.3. Each of 12 families studied was compatible with linkage to the marker D19S886. We have analysed 20 further families and found that the majority of these are consistent with a PJS gene on 19p13.3. Three families were, however, unlinked to 19p13.3 and none of the available PJS polyps from these families showed allele loss at D19S886. There were no obvious clinicopathological or ethnic differences between the 19p13.3 linked and unlinked families. There appears, therefore, to be a major PJS locus on chromosome 19p13.3 and the possibility exists of a minor locus (or loci) elsewhere.