Hereditary cancers disclose a class of cancer genes

Retinoblastoma and the genetic theory of cancer: an old paradigm trying to survive to the evidence

Retinoblastoma (Rb) is considered to represent the prototype of cancer linked to the sequential loss or inactivation of both alleles of a so-called “tumor suppressor gene”, the Rb1 gene. The pathogenetic mechanism behind this tumor was first hypothesized by Knudson in 1971 and further confirmed by others who identified the Rb1 gene whose loss or inactivation was claimed to be responsible for the disease. However, after about four decades of continuous research in the field of molecular biology, the evidence behind the role of the Rb1 gene in Rb appears to be seriously flawed in the light of epidemiological, biological, and clinical evidences. This editorial summarizes the inconsistencies on this subject. Nevertheless, the molecular biology establishment still adheres to the biased view of the genetic origin of Rb and other cancers, and hardly any alternative explanations are taken into account.

Pulmonary preneoplasia--sequential molecular carcinogenetic events

Bronchial and bronchioloalveolar carcinogenesis is a multicentric and multistep process, leading to a sequential accumulation of molecular and genetic abnormalities, mainly due to exposure to tobacco carcinogens. Concomitantly, a series of morphological alterations of normal bronchial or bronchioloalveolar epithelium occur, resulting in preneoplastic and then neoplastic lesions. The three pulmonary preneoplastic changes recognized to date in the lung include bronchial squamous dysplasia and in situ carcinoma, preceding invasive squamous cell carcinoma and basaloid carcinoma, atypical adenomatous hyperplasia, a preneoplastic condition of bronchioloalveolar carcinoma, and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia, a proposed precursor for carcinoid tumours. Although the gradual accumulation of molecular alterations has been widely investigated in bronchial carcinogenesis, with the aim of determining new biomarkers for early lung cancer detection in high-risk patients and targeted chemoprevention, lung adenocarcinoma pathogenesis has been only recently highlighted, with the recent discovery of epidermal growth factor receptor mutation pathway in non-smokers. This review focuses on the current status of molecular pathology in lung cancer and pulmonary preneoplastic conditions.

Molecular Basis of Pulmonary Disease

Pulmonary pathology includes a large spectrum of both neoplastic and non-neoplastic diseases that affect the lung. Many of these are a result of the unusual relationship of the lung with the outside world. Every breath that a human takes brings the outside world into the body in the form of infectious agents, organic and inorganic particles, and noxious agents of all types. Although the lung has many defense mechanisms to protect itself from these insults, these are not infallible; therefore, lung pathology arises. Damage to the lung is particularly important given the role of the lung in the survival of the organism. Any impairment of lung function has widespread effects throughout the body, since all organs depend on the lungs for the oxygen they need. Pulmonary pathology catalogs the changes in the lung tissues and the mechanisms through which these occur. This chapter presents a review of lung pathology and the current state of knowledge about the pathogenesis of each disease. It suggests that a clear understanding of both morphology and mechanism is required for the development of new therapies and preventive measures.

Molecular pathology of thymic epithelial neoplasms

The etiology and molecular pathogenesis of thymic tumors are unknown. However, during the last two decades there has been some progress on elucidating the genetic abnormalities present and molecular pathways altered in thymic tumors. These abnormalities, while bearing distinctions and similarities to those described in other tumors, can be organized under the "hallmarks of cancer," as proposed by Hanahan and Weinberg. These changes include self-sufficiency in growth signaling, insensitivity to antigrowth signals, ability to evade apoptosis, limitless replicative potential, ability to sustain angiogenesis, and tissue invasion and metastasis. However, this progress is still limited and has not led to better tumor classifications, prognostication of outcome, and design of molecular targeted therapy.

Lung cancer preneoplasia

From histological and biological perspectives, lung cancer is a complex neoplasm. Although the sequential preneoplastic changes have been defined for centrally arising squamous carcinomas of the lung, they have been poorly documented for the other major forms of lung cancers, including small cell lung carcinoma and adenocarcinomas. There are three main morphologic forms of preneoplastic lesions recognized in the lung: squamous dysplasias, atypical adenomatous hyperplasia, and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia. However, these lesions account for the development of only a subset of lung cancers. Several studies have provided information regarding the molecular characterization of lung preneoplastic changes, especially for squamous cell carcinoma. These molecular changes have been detected in the histologically normal and abnormal respiratory epithelium of smokers. Two different molecular pathways have been detected in lung adenocarcinoma pathogenesis: smoking-associated activation of RAS signaling, and nonsmoking-associated activation of EGFR signaling; the latter is detected in histologically normal respiratory epithelium.

Molecular pathogenesis of early-stage non-small cell lung cancer and a proposal for tissue banking to facilitate identification of new biomarkers

Non-small cell lung carcinoma (NSCLC) is one of the leading causes of death from cancer in both Eastern and Western countries. For patients with stage I NSCLC, full lobar or more extensive surgical resection is the treatment of choice. However, even among patients with surgically resected, stage I NSCLC, up to 30% of patients die of the disease within 5 years. At present, apart from clinical stage, there are no established cancer-specific clinical variables or biomarkers that reliably identify individuals at increased risk of death after surgical resection-individuals who could be candidates for adjuvant therapy or alternative management strategies. At a recent international workshop, participants discussed a clinical trial to compare radiation therapy with surgery among patients with stage I NSCLC. This study offers the opportunity to prospectively obtain, bank, and analyze tissue and other clinical specimens, which should facilitate the identification of new biomarkers for early detection, prognosis, and therapy in lung cancer.

Retinoblastoma epidemiology: does the evidence matter?

It has been proposed that retinoblastoma is 'caused' by two sequential mutations affecting the RB1 gene, but this is a rather outdated view of cancer aetiology that does not take into account a large amount of new acquisitions such as chromosomal and epigenetic alterations. Retinoblastoma remains probably the only cancer in which the rather simplistic 'two hit' mutational model is still considered of value, although cancer is known to be associated with genomic and microsatellite instability, defects of the DNA mismatch repair system, alterations of DNA methylation and hystone acethylation/deacethylation, and aneuploidy. Moreover, as it is shown herein, the predictions made by the 'two hit' model, are not fulfilled by the clinical and epidemiological data reported so far. Moreover, while the role of mutational events in cancer has been largely questioned in the more recent literature, no serious effort has been done to investigate the role of epigenetic alterations and aneuploidy in retinoblastoma. Through the analysis of the specialised literature and a set of original epidemiological and biological data concerning retinoblastoma, the authors illustrate the evidences arguing against the 'two hit' hypothesis and propose that epigenetic factors and aneuploidy play central roles in the disease.

Emergentism as a default: cancer as a problem of tissue organization

During the last fifty years the dominant stance in experimental biology has been reductionism. For the most part, research programs were based on the notion that genes were in 'the driver's seat' controlling the developmental program and determining normalcy and disease (genetic reductionism and genetic determinism). Philosophers were the first to realize that the belief that the Mendelian genes were reduced to DNA molecules was questionable. Soon after these pronouncements, experimental data confirmed their misgivings. The optimism of molecular biologists, fueled by early success in tackling relatively simple problems, has now been tempered by the difficulties found when attempting to understand complex biological problems. Here, we analyse experimental data that illustrate the shortcomings of this sort of reductionism. We also examine the prevailing paradigm in cancer research, the somatic mutation theory (SMT), the premises of which are: (i) cancer is derived from a single somatic cell that has accumulated multiple DNA mutations; (ii) the default state of cell proliferation in metazoa is quiescence; and (iii) cancer is a disease of cell proliferation caused by mutations in genes that control proliferation and the cell cycle. We challenge the notion that cancer is a cellular problem caused by mutated genes by assessing data gathered both from within the reductionist paradigm and from an alternative view that regards carcinogenesis as a developmental process gone awry. This alternative view, explored under the name of the tissue organization field theory (TOFT), is based on premises that place cancer in a different hierarchical level of complexity from that proposed by the SMT, namely: (i) carcinogenesis represents a problem of tissue organization comparable to organogenesis, and (ii) proliferation is the default state of all cells. We propose that the organicist view, in which the TOFT is based, is a good starting point from which to explore emergent phenomena. However, new theoretical concepts are needed in order to grapple with the apparent circular causality of complex biological phenomena in development and carcinogenesis.

The contribution of genetic and epigenetic changes in granulosa cell tumors of ovarian origin

PURPOSE

Granulosa cell tumors (GCTs) are relatively rare and are subtypes of the sex-cord stromal neoplasms. A better understanding of the molecular genetics underlying various steps in malignant transformation is critical to success in the battle against this disease. Changes in the status of methylation, known as epigenetic alterations, are one of the most common molecular alterations in human cancers, including GCTs. Chromosomal instability and microsatellite instability (MSI) are common in these GCTs. We tested the hypothesis that C-->T transition polymorphism in the promoter region of cytosine DNA-methyltransferase-3B (DNMT3B) and its altered expression are also associated with hypermethylation of the genes. We also attempted to determine the relationship between MSI of ovarian carcinoma and hMLH1 hypermethylation in these tumors.

EXPERIMENTAL DESIGN

We studied chromosome instability in 25 GCTs by detecting gross chromosome rearrangements in cultured peripheral blood lymphocytes. MSI was assessed using six microsatellite markers (BAT25, BAT26, D2S123, D5S346, D11S1318, and D17S250). Using sensitive methylation-specific PCR, we searched for aberrant promoter hypermethylation in a panel of genes including p16, BRCA1, RASSF1A, ER-alpha, TMS1, TIMP3, Twist, GSTP1, AR, and hMLH1. Polymorphism in the DNMT3B gene was assessed by the PCR-RFLP method, and DNMT3B expression was studied by reverse transcription-PCR assay.

RESULTS

Chromosome instability was indicated by significantly higher frequencies of chromosome aberrations (6.24%; P < 0.001) compared with controls (2.12%). The most frequently observed changes include trisomy 14 and monosomy 22. MSI has been found in 19 of 25 tumors, and loss of heterozygosity has been found in 9 of 25 tumors. Frequencies of methylation in GCTs were 40% for p16 and ER-alpha; 36% for BRCA1 and RASSF1A; 28% for hMLH1; 24% for TIMP3, Twist, and GSTP1; and 20% in TMS1 and AR. TT genotype was found only in two cases; the remainder were either CC or CT type. There was no significant alteration in the expression of DNMT3B in these patients.

CONCLUSIONS

Coexistence of chromosome instability, MSI, and hypermethylation suggests that both genetic and epigenetic mechanisms may act in concert to inactivate the above-mentioned genes in these GCTs. These mechanisms can be an early event in the pathogenesis of these tumors, and it can be a critical step in the tumorigenic process. All these events might play an important role in early clinical diagnosis and in chemotherapeutic management and treatment of the disease. Larger studies may lend further understanding to the etiology and clinical behavior of these tumors.

European multi-centre case-control study on risk factors for rare cancers of unknown aetiology

To search for occupational risk factors, we conducted a case-control study in nine European countries of cancers of the small intestine, male gall bladder, thymus, bone, male breast, melanoma of the eye, and mycosis fungoides. Recruitment was population based in Denmark, Latvia, France, Germany, Italy, and Sweden, from hospital areas in Spain and Portugal, and from one United Kingdom (UK) hospital. We recruited 1457 cases (84% interviewed). Numbers identified corresponded to those in the EUROCIM database for Denmark, but were below those observed for France, Italy and Sweden in the database. We recruited 3374 population (61% interviewed) and 1284 colon cancer controls (86% interviewed). It was possible to undertake this complicated study across Europe, but we encountered three main problems. It was difficult to ensure complete case ascertainment, for population controls, we found a clear divide in the response rate from 75% in the South to only 55% in the North, and a somewhat selective recruitment was noted for the colon cancer controls. The study showed there is a clear dose-response relationship between alcohol intake and the risk of male breast cancer, and an excess risk of mycosis fungoides among glass formers, pottery and ceramic workers. Further data are expected.

The somatic mutation theory of cancer: growing problems with the paradigm?

The somatic mutation theory has been the prevailing paradigm in cancer research for the last 50 years. Its premises are: (1) cancer is derived from a single somatic cell that has accumulated multiple DNA mutations, (2) the default state of cell proliferation in metazoa is quiescence, and (3) cancer is a disease of cell proliferation caused by mutations in genes that control proliferation and the cell cycle. From this compelling simplicity, an increasingly complicated picture has emerged as more than 100 oncogenes and 30 tumor suppressor genes have been identified. To accommodate this complexity, additional ad hoc explanations have been postulated. After a critical review of the data gathered from this perspective, an alternative research program has been proposed. It is based on the tissue organization field theory, the premises of which are that carcinogenesis represents a problem of tissue organization, comparable to organogenesis, and that proliferation is the default state of all cells. The merits of these competing theories are evaluated herein.

Small cell lung cancer: from molecular biology to novel therapeutics

Small cell lung cancer (SCLC) is an aggressive tumor which metastasizes early. Patients with this disease have a poor prognosis even with immediate treatment. Because of the aggressive nature of this disease, all aspects of this tumor are studied extensively. This review will provide an update of the biology of SCLC at both the molecular and cellular levels. Cellular pathways and their relationship to cellular function will also be discussed. Treatment of both primary limited- and extensive-stage diseases as well as recurrent disease will be discussed including chemotherapy, thoracic radiotherapy, and surgery. The role of novel therapeutics being investigated will also be addressed.

Fragile histidine triad (FHIT) gene abnormalities in lung cancer

Lung cancer is the most common cause of cancer death in the world. In recent years, enormous progress has been made in understanding the molecular and cellular biology of lung cancer. The fragile histidine triad (FHIT) gene, a candidate tumor-suppressor gene, was recently identified at chromosome 3p14.2, spanning the FRA3B common fragile site. Frequent allelic losses as well as homozygous deletions have been described at the FHIT locus, making FHIT a strong candidate as a tumor-suppressor gene. However, the occurrence of mutations is very rare. Aberrant FHIT transcripts, including deletions of exons, insertions between exons, and insertions replacing exons, are detected in a high percentage of lung tumors. Reduction or complete loss of FHIT expression by immunohistochemical testing is seen in about 30%-70% of non small-cell lung cancer and in about 20% of bronchial biopsies from chronic smokers without evidence of lung cancer. This finding supports the theory that FHIT is a molecular target of tobacco smoke carcinogens. However, the location of the gene in one of the most fragile sites of the human genome and the paucity of mutations have led to an alternative hypothesis that abnormalities of the gene are bystander effects resulting from disruption of the FRA3B locus. Thus, the function of FHIT as a candidate tumor-suppressor gene is still controversial, and additional studies are necessary to clarify the role of FHIT in lung cancer pathogenesis.

Smoking molecular damage in bronchial epithelium

Our understanding of the molecular pathology of lung cancer is advancing rapidly with several specific genes and chromosomal regions being identified. Lung cancer appears to require many mutations in both dominant and recessive oncogenes to possess malignant phenotypes. Several genetic and epigenetic changes are common to all lung cancer histologic types, while others appear to be cell type specific. However, specific roles of the genes undergoing mutations and the order of cumulative molecular changes that lead to the development of each lung tumor histologic type remain to be fully elucidated. Recent findings of molecular abnormalities in normal appearing and preneoplastic bronchial epithelium from patients with lung cancer and chronic smokers suggest that genetic changes may serve as biomarkers for early diagnosis, risk assessment and monitoring response to chemoprevention.

Are there two sides to colorectal cancer?

Colorectal carcinomas (CRC) that arise proximal (right) or distal (left) to the splenic flexure exhibit differences in incidence according to geographic region, age and gender. Together with observations that tumours in the hereditary cancer syndromes HNPCC and FAP occur predominantly in the right and left colon, respectively, the existence of 2 categories of CRC based on site of origin in the large bowel was proposed more than a decade ago. Differences between normal right and left colonic segments that could favour progression through different tumourigenic pathways are summarized in this review. Accumulating evidence suggests that the risk of CRC conferred by various environmental and genetic factors is different for proximal and distal tumours. Right- and left-sided tumours also exhibit different sensitivities to fluorouracil-based chemotherapy. Such differences are probably related to the molecular characteristics of the tumours, with the microsatellite instability and CpG island methylator phenotypes being associated with right-sided tumours and chromosomal instability with left-sided tumours. Future molecular-based classification systems for CRC that rely upon distinctive gene expression patterns may allow a clearer discrimination of subgroups than that provided by tumour site alone. Until then however, the existence of 2 broadly different groups of cancer defined by site of origin in the colon should be considered in the design of future epidemiologic studies as well as in the design of new clinical trials aimed at testing novel adjuvant therapies.

Molecular pathogenesis of lung cancer

Lung cancer is the most common cause of cancer death in the United States, killing more than 156,000 people every year. In the past two decades, significant progress has been made in understanding the molecular and cellular pathogenesis of lung cancer. Abnormalities of proto-oncogenes, genetic and epigenetic changes of tumor suppressor genes, the role of angiogenesis in the multistage development of lung cancer, as well as detection of molecular abnormalities in preinvasive respiratory lesions, have recently come into focus. Efforts are ongoing to translate these findings into new clinical strategies for risk assessment, chemoprevention, early diagnosis, treatment selection, and prognosis and to provide new targets and methods of treatment for lung cancer patients. All these strategies should aid in reducing the number of newly diagnosed lung cancer cases and in increasing the survival and quality of life of patients with lung cancer.

Loss of heterozygosity analysis defines a 3-cM region of 15q commonly deleted in human malignant mesothelioma

Previous comparative genomic hybridization and allelic loss analyses demonstrated frequent deletions from 15q11.1-15 in malignant mesothelioma. Recurrent losses of 15q11-22 have also been reported in several other tumor types such as breast and colorectal cancers. To more precisely map the commonly deleted region, we have performed a high density loss of heterozygosity analysis of 46 malignant mesotheliomas, using 26 polymorphic microsatellite markers spanning the entire long arm of chromosome 15. Allelic loss from 15q was observed in 22 of 46 (48%) cases. These analyses have defined a minimally deleted region of approximately 3-cM, which was confirmed to reside at 15q15 by fluorescence in situ hybridization analysis with yeast artificial chromosome probes. No tumor suppressor genes have been reported to map to this site. The minimally deleted region identified in this investigation overlaps those observed in other kinds of cancer, and is the smallest site of recurrent 15q loss identified to date in human tumors. The identification of this commonly deleted site implicates a putative tumor suppressor gene(s) at 15q15 involved in diverse forms of human neoplasia.

Promoter methylation and silencing of the retinoic acid receptor-beta gene in lung carcinomas

BACKGROUND

Retinoic acid plays an important role in lung development and differentiation, acting primarily via nuclear receptors encoded by the retinoic acid receptor-beta (RARbeta) gene. Because receptor isoforms RARbeta2 and RARbeta4 are repressed in human lung cancers, we investigated whether methylation of their promoter, P2, might lead to silencing of the RARbeta gene in human lung tumors and cell lines.

METHODS

Methylation of the P2 promoter from small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) cell lines and tumor samples was analyzed by the methylation-specific polymerase chain reaction (PCR). Expression of RARbeta2 and RARbeta4 was analyzed by reverse transcription-PCR. Loss of heterozygosity (LOH) was analyzed by PCR amplification followed by electrophoretic separation of PCR products. Statistical differences were analyzed by Fisher's exact test with continuity correction.

RESULTS

The P2 promoter was methylated in 72% (63 of 87) of SCLC and in 41% (52 of 127) of NSCLC tumors and cell lines, and the difference was statistically significant (two-sided P:<.001). By contrast, in 57 of 58 control samples, we observed only the unmethylated form of the gene. Four tumor cell lines with unmethylated promoter regions expressed both RARbeta2 and RARbeta4. Four tumor lines with methylated promoter regions lacked expression of these isoforms, but demethylation by exposure to 5-aza-2'-deoxycytidine restored their expression. LOH at chromosome 3p24 was observed in 100% (13 of 13) of SCLC lines and 67% (12 of 18) of NSCLC cell lines, and the difference was statistically significant (two-sided P: =.028).

CONCLUSIONS

Methylation of the RARbeta P2 promoter is one mechanism that silences RARbeta2 and RARbeta4 expression in many lung cancers, particularly SCLC. Chemical demethylation is a potential approach to lung cancer therapy.

Cell cycle control, checkpoint mechanisms, and genotoxic stress

The ability of cells to maintain genomic integrity is vital for cell survival and proliferation. Lack of fidelity in DNA replication and maintenance can result in deleterious mutations leading to cell death or, in multicellular organisms, cancer. The purpose of this review is to discuss the known signal transduction pathways that regulate cell cycle progression and the mechanisms cells employ to insure DNA stability in the face of genotoxic stress. In particular, we focus on mammalian cell cycle checkpoint functions, their role in maintaining DNA stability during the cell cycle following exposure to genotoxic agents, and the gene products that act in checkpoint function signal transduction cascades. Key transitions in the cell cycle are regulated by the activities of various protein kinase complexes composed of cyclin and cyclin-dependent kinase (Cdk) molecules. Surveillance control mechanisms that check to ensure proper completion of early events and cellular integrity before initiation of subsequent events in cell cycle progression are referred to as cell cycle checkpoints and can generate a transient delay that provides the cell more time to repair damage before progressing to the next phase of the cycle. A variety of cellular responses are elicited that function in checkpoint signaling to inhibit cyclin/Cdk activities. These responses include the p53-dependent and p53-independent induction of Cdk inhibitors and the p53-independent inhibitory phosphorylation of Cdk molecules themselves. Eliciting proper G1, S, and G2 checkpoint responses to double-strand DNA breaks requires the function of the Ataxia telangiectasia mutated gene product. Several human heritable cancer-prone syndromes known to alter DNA stability have been found to have defects in checkpoint surveillance pathways. Exposures to several common sources of genotoxic stress, including oxidative stress, ionizing radiation, UV radiation, and the genotoxic compound benzo[a]pyrene, elicit cell cycle checkpoint responses that show both similarities and differences in their molecular signaling.

Cancer control in susceptible groups: opportunities and challenges

Cancer mortality rates in the United States have risen throughout most of this century, and a downward trend has just emerged in recent years. Nevertheless, it is predicted that cancer will soon be the leading cause of death among Americans. To gain new knowledge of etiology, we have studied persons at highest risk as human models of cancer susceptibility. Clinical observations at the bedside are used to generate etiologic hypotheses that are tested in epidemiologic studies. Companion laboratory studies can identify biologic mechanisms of predisposition. Data show that inborn mutations in cancer-predisposing genes, such as BRCA1 and BRCA2, markedly increase the risk of cancers at unusually early ages. Increasing numbers of these highly penetrant genes are being identified. These discoveries have created new opportunities for genetic testing to identify cancer-prone individuals. Individuals found to be carriers can be offered counseling to avoid environmental exposures that further elevate risk, intensive medical surveillance for early detection, participation in chemoprevention trials, and prophylactic surgery to remove at-risk tissues. However, genetic knowledge can have adverse effects, including psychologic distress, social stigmatization, and loss of health insurance. Research is needed to maximize benefits and minimize risks to the susceptible populations. Professional and public education can promote appropriate use of genetic data, and legislation may be required to prevent discrimination. Knowledge of these highly penetrant genes can be extended to common polymorphisms that modify cancer risk associated with exposures to environmental carcinogens.

Chromosome aberrations and sister chromatid exchange studies in patients with prostate cancer: possible evidence of chromosome instability

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 24 patients with prostate cancer. Of these, eight belong to stage B, six to stage C/e, three to C/sv, two to Do, and the remaining five to DI stage of carcinoma. Simultaneously, sister chromatid exchanges (SCEs) were also analyzed in the peripheral blood lymphocytes of these patients, along with those of 40 age-matched control subjects. The frequency of aberrant metaphases is significantly higher in patients with prostate cancer (7.32%) than in age-matched controls (2.92%). A large number of chromosome aberrations in lymphocytes of these patients, which are generally constitutional in nature, have also been detected. In stage-B patients, the frequency of cytogenetically abnormal cells is comparatively low with regard to the number of cells scanned, and these abnormalities are generally confined only to single chromosome (except in one metaphase in patient 1, who was diagnosed with bladder carcinoma in addition to cancer of the prostate). Sister chromatid exchanges (SCEs) were also analyzed in the patients and age-matched control subjects. The mean SCE frequencies were 9.24 +/- 0.62 (n = 1356) per metaphase and 0.203 per chromosome in patients, whereas in control subjects the frequencies were 5.94 +/- 0.25 (n = 4000) per metaphase and 0.129 per chromosome. The SCE frequency in cancer patients was statistically significant (p < 0.001). Our results indicate that the patients with prostate cancer show a degree of chromosomal instability that might be related to a predisposition to neoplasia.

Retinoblastoma protein family in cell cycle and cancer: a review

Two genes, p107 and Rb2/p130, are strictly related to RB, the most investigated tumor suppressor gene, responsible for susceptibility to retinoblastoma. The products of these three genes, namely pRb, p107, and pRb2/p130 are characterized by a peculiar steric conformation, called "pocket," responsible for most of the functional interactions characterizing the activity of these proteins in the homeostasis of the cell cycle. The interest in these genes and proteins springs from their ability to regulate cell cycle processes negatively, being able, for example, to dramatically slow down neoplastic growth. So far, among these genes, only RB is firmly established to act as a tumor suppressor, because its lack-of-function is clearly involved in tumor onset and progression. It has been found deleted or mutated in most retinoblastomas and sarcomas, but its inactivation is likely to play a crucial role in other types of human cancers. The two other members of the family have been discovered more recently and are currently under extensive investigation. We review analogies and differences among the pocket protein family members, in an attempt to understand their functions in normal and cancer cells.

Choromosome instabililty and sister chromatid exchange (SCE) studies in patients with carcinoma of cervix uteri

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 14 patients with carcinoma of the cervix uteri. Simultaneously, sister chromatid exchange (SCE) was also analyzed in the peripheral blood lymphocytes of these patients, along with those of 20 age-matched control subjects. The frequency of aberrant metaphases is significantly higher in patients with carcinoma of the cervix uteri (7.85%) than in the age-matched controls (3.35%). A large number of chromosome aberrations in lymphocytes of these patients have also been detected. Sister chromatid exchange (SCE) was also analyzed in lymphocytes of 14 patients with carcinoma of the cervix uteri and 20 age-matched control subjects. The mean SCE frequencies were 9.44 +/- 0.34 (n = 637) and 6.09 +/- 0.24 (n = 900) per metaphase in patients and controls, respectively. The increase of SCE frequency in cancer patients was statistically significant (p < 0.001), but not seen in controls. Our results suggest that patients with carcinoma of the cervix uteri show a degree of chromosomal instability that might be related to a predisposition to neoplasia.

p53 and the Li-Fraumeni syndrome

The Li-Fraumeni familial cancer syndrome was initially described in 1969 in a retrospective epidemiologic review of more than 600 pediatric sarcoma patients. The clinical definition of the syndrome has been refined in the last two decades by prospective analyses of several families. Despite these exhaustive studies, the gene or genes responsible for the unusual constellation of tumors in these families remained elusive until 1990, when it was demonstrated that germline abnormalities of the p53 tumor suppressor gene could account for the occurrence of cancer in many classic Li-Fraumeni families. Identification of the molecular events that yield this phenotype has led many researchers to pursue several lines of investigation to improve our understanding of the significance of such alterations. We discuss the clinical, epidemiologic, genetic, and biologic aspects of the association between p53 and the Li-Fraumeni family cancer syndrome.

Tumour suppressor genes and colorectal neoplasia

Two distinct gene classes have been implicated in colorectal carcinogenesis. Tumour promoter genes (oncogenes, dominant oncogenes) produce an excessive positive stimulus to cell proliferation. The ras family of oncogenes are an example. Acquired mutations of the c-k-ras gene are commonly found in colonic adenomas and carcinomas. Tumour suppressor genes (anti-oncogenes, recessive oncogenes) normally constrain or regulate cell proliferation. Loss of this function through gene deletion or mutation is oncogenic. Inherited tumour suppressor gene mutations have now been identified in several of the familial cancer syndromes. Acquired tumour suppressor gene mutations are found in both sporadic and hereditary cancers. Together with the tumour promoter genes they provide the genetic basis for the cellular changes occurring during carcinogenesis. The retinoblastoma gene was the first human tumour suppressor gene to be characterized and exemplifies the class. More recently, linkage studies in the hereditary cancer syndromes and the detection of specific deletions in sporadic tumours have helped to identify several new tumour suppressor genes. At least four of these (MCC, APC, p53 and DCC) apparently contribute to sporadic colorectal carcinogenesis. Germ line APC mutations produce the inherited colorectal cancer syndrome familial adenomatous polyposis (FAP). Detection of these mutations using linked markers has already found clinical application in the screening of families with this disease. In the future, genetic diagnosis of hereditary non-polyposis colorectal cancer (HNPCC) and the recognition of those genetically susceptible to sporadic colorectal cancer may become possible. At the same time, as our understanding of the genes involved improves, new avenues for treatment and prevention of colorectal cancer may emerge.

Molecular genetics of human malignant melanoma

Due to a variety of known and unknown control mechanisms, the human genome is remarkably stable when compared to most other species. The long latency periods of most solid tumors, during which the cell undergoes malignant transformation, are presumably due to this stability. The molecular basis responsible for the induction of genetic instability and the resultant biological characteristics manifest in tumor populations is not well understood. The discovery of both oncogenes and tumor suppressor genes, however, has placed the phenomenon of human genome stability on a more solid conceptual footing. These types of genes clearly place multiple barriers to oncogenic transformation, and traversing these barriers apparently requires both time and the accumulation of genetic defects that cannot be corrected. The evolution of neoplasias can, therefore, be predicted to be due to: (1) consistent and progressive loss of tumor suppressor genes; (2) gene amplification, resulting in the over-expression of proteins that aid in tumor progression; (3) gene mutation, which alters the orderly biochemistry of the normal cell; (4) genes that allow a cell like the melanocyte to escape the confining nature of the epidermis and to invade through the dermis into the circulatory and lymphatic systems in order to disseminate itself to other organs (e.g., proteolytic enzymes, enzyme inhibitors, integrins, metastases genes, chemotactic factors etc.); (5) factors, perhaps such as TGF beta 2, that may impact negatively on MHC antigens and confuse host defense mechanisms; and (6) S.O.S.-type genes, which may be expressed as a direct response to the accumulating damage in an attempt to correct the damage, but that may then become part of the problem instead of the solution. The extraordinary plasticity and instability of the genome of a melanoma cell suggests an inordinate amount of genetic flux. In addition to activating and inactivating various genes, this constant shuffling and rearranging of the genome in neoplasms such as MM may be constantly altering gene dose. Cytogenetic and molecular biological studies have been the Rosetta stone for understanding the etiological relevant genetic events in human cancers. Genetic alterations fundamental to the pathology of MM have begun to be defined. Studies designed to understand these perturbations at the biochemical and organismic level are underway.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytogenetic study of a nodular hyperplasia of the thyroid after irradiation for Hodgkin's disease

We describe cytogenetics of a case of nodular hyperplasia of the thyroid with papillary microcarcinoma following radiotherapy for Hodgkin's disease. The chromosomal pattern found was very heterogeneous with a clonal abnormality of chromosome 10, among others. Together with some recent data from the literature, this finding may point to an important role of chromosome 10 abnormalities in the pathogenesis of benign and malignant thyroid neoplasms.

The prognostic value of DNA-ploidy in colorectal carcinoma: a prospective study

One hundred and fifty-seven patients with usual colorectal cancer were analysed prospectively for DNA-ploidy, DNA-index and S-phase fraction (SPF) using flow cytometry. An abnormal DNA-stemline was observed in 68% of tumours. The patients have been followed for a median of 36 months. In univariate analysis, tumour stage was the most significant prognostic factor. After excluding patients with stage D disease, DNA-aneuploidy was significantly associated with a shorter survival and a shorter disease free survival. SPF, however, did not correlate with prognosis. In multiple samples from the same tumour there was on average a 29% difference between the highest and the lowest SPF indicating considerable heterogeneity in proliferative activity within the tumours. In diploid tumours the variation was even higher. Patients with proximal tumours as well as female patients had DNA-diploid tumours more often than the others. This may indicate that there are different, so far unknown, aetiological factors leading to different types of ploidy pattern.