Deletions of a DNA sequence in retinoblastomas and mesenchymal tumors: organization of the sequence and its encoded protein

Diagnostic and Prognostic/Therapeutic Significance of Comprehensive Analysis of Bone and Soft Tissue Tumors Using Optical Genome Mapping and Next-Generation Sequencing

Detecting somatic structural variants (SVs), copy number variants (CNVs), and mutations in bone and soft tissue tumors is essential for accurately diagnosing, treating, and prognosticating outcomes. Optical genome mapping (OGM) holds promise to yield useful data on SVs and CNVs but requires fresh or snap-frozen tissues. This study aimed to evaluate the clinical utility of data from OGM compared with current standard-of-care cytogenetic testing. We evaluated 60 consecutive specimens from bone and soft tissue tumors using OGM and karyotyping, fluorescence in situ hybridization, gene fusion assays, and deep next-generation sequencing. OGM accurately identified diagnostic SVs/CNVs previously detected by karyotyping and fluorescence in situ hybridization (specificity = 100%). OGM identified diagnostic and pathogenic SVs/CNVs (∼23% of cases) undetected by karyotyping (cryptic/submicroscopic). OGM allowed the detection and further characterization of complex structural rearrangements including chromoanagenesis (27% of cases) and complex 3- to 6-way translocations (15% of cases). In addition to identifying 321 SVs and CNVs among cases with chromoanagenesis events, OGM identified approximately 9 SVs and 12 CNVs per sample. A combination of OGM and deep next-generation sequencing data identified diagnostic, disease-associated, and pathogenic SVs, CNVs, and mutations in ∼98% of the cases. Our cohort contained the most extensive collection of bone and soft tissue tumors profiled by OGM. OGM had excellent concordance with standard-of-care cytogenetic testing, detecting and assigning high-resolution genome-wide genomic abnormalities with higher sensitivity than routine testing. This is the first and largest study to provide insights into the clinical utility of combined OGM and deep sequencing for the pathologic diagnosis and potential prognostication of bone and soft tissue tumors in routine clinical practice.

Hereditary Conditions Associated with Elevated Cancer Risk in Childhood

Received January, 31, 2023 Revised March, 16, 2023 Accepted March, 18, 2023 Widespread use of the next-generation sequencing (NGS) technologies revealed that a significant percentage of tumors in children develop as a part of monogenic hereditary diseases. Predisposition to the development of pediatric neoplasms is characteristic of a wide range of conditions including hereditary tumor syndromes, primary immunodeficiencies, RASopathies, and phakomatoses. The mechanisms of tumor molecular pathogenesis are diverse and include disturbances in signaling cascades, defects in DNA repair, chromatin remodeling, and microRNA processing. Timely diagnosis of tumor-associated syndromes is important for the proper choice of cancer treatment, genetic counseling of families, and development of the surveillance programs. The review describes the spectrum of neoplasms characteristic of the most common syndromes and molecular pathogenesis of these diseases.

Understanding Retinoblastoma Post-Translational Regulation for the Design of Targeted Cancer Therapies

Simple Summary

Rb1 is a regulator of cell cycle progression and genomic stability. This review focuses on post-translational modifications, their effect on Rb1 interactors, and their role in intracellular signaling in the context of cancer development. Finally, we highlight potential approaches to harness these post-translational modifications to design novel effective anticancer therapies.

Abstract

The retinoblastoma protein (Rb1) is a prototypical tumor suppressor protein whose role was described more than 40 years ago. Together with p107 (also known as RBL1) and p130 (also known as RBL2), the Rb1 belongs to a family of structurally and functionally similar proteins that inhibits cell cycle progression. Given the central role of Rb1 in regulating proliferation, its expression or function is altered in most types of cancer. One of the mechanisms underlying Rb-mediated cell cycle inhibition is the binding and repression of E2F transcription factors, and these processes are dependent on Rb1 phosphorylation status. However, recent work shows that Rb1 is a convergent point of many pathways and thus the regulation of its function through post-translational modifications is more complex than initially expected. Moreover, depending on the context, downstream signaling can be both E2F-dependent and -independent. This review seeks to summarize the most recent research on Rb1 function and regulation and discuss potential avenues for the design of novel cancer therapies.

13q interstitial deletion in a moroccan child with hereditary retinoblastoma and intellectual disability: A case report

Retinoblastoma is the most common malignant tumor of the eye in children (incidence:1/15,000 to 1/20,000 births), with a sex ratio of 1,5/1. Retinoblastoma, in its inherited form, is a disease caused by a syndrome of genetic predisposition to cancer. The RB1 gene, a tumor suppressor gene, is localized at 13q14. This case report shows the indication of the cytogenetic analysis in the management of patients with retinoblastoma, and the interest of a genetic counseling. We report the medical observation of a five and a half years old patient who was followed in the medical genetic's department for intellectual disability: associated with facial dysmorphia. The cytogenetic study objectified the presence of an interstitial deletion of the long arm of chromosome 13: 46, XX, del (13) (q14q22). A genetic counseling, with study of the karyotype of the parents is planned, specially to search for a balanced insertion: 13q14 insertion and deletion. In addition, the patient has been followed since the age of 9 months at the pediatric ophthalmology department for a bilateral retinoblastoma, in remission. A subject carry in constitutional mutation of the RB1 gene has a greater than 90% risk of developing retinoblastoma, and moreover has a genetic predisposition to secondary tumors. This medical observation shows the benefit of the constitutional cytogenetic study for patients with retinoblastoma, in particular in the event of bilateral retinoblastoma. The monitoring of psychomotor development must supplement the ophthalmological monitoring of these patients, with a systematic genetic counseling.

[Research on Analysis of Final Diagnosis and Prognostic Factors, and Development of New Therapeutic Drugs for Malignant Tumors (Especially Malignant Pediatric Tumors)]

Outcomes of treatment for malignant pediatric tumors including leukemia are improving by conventional multimodal treatment with strong chemotherapy, surgical resection, radiotherapy, and bone marrow transplantation. However, patients with advanced neuroblastoma, metastatic Ewing's sarcoma family of tumor (ESFT), and metastatic osteosarcoma continue to have an extremely poor prognosis. Therefore novel therapeutic strategies are urgently needed to improve their survival. Apoptotic cell death is a key mechanism for normal cellular homeostasis. Intact apoptotic mechanisms are pivotal for embryonic development, tissue remodeling, immune regulation, and tumor regression. Genetic aberrations disrupting programmed cell death often underpin tumorigenesis and drug resistance. Moreover, it has been suggested that apoptosis or cell differentiation proceeds to spontaneous regression in early stage neuroblastoma. Therefore apoptosis or cell differentiation is a critical event in this cancer. We extracted many compounds from natural plants (Angelica keiskei, Alpinia officiarum, Lycaria puchury-major, Brassica rapa) or synthesized cyclophane pyridine, indirubin derivatives, vitamin K3 derivatives, burchellin derivatives, and GANT61, and examined their effects on apoptosis, cell differentiation, and cell cycle in neuroblastoma and ESFT cell lines compared with normal cells. Some compounds were very effective against these tumor cells. These results suggest that they may be applicable as an efficacious and safe drug for the treatment of malignant pediatric tumors.

Onco-Suppressor Genes in Human Cancer

The analysis of the molecular mechanisms governing multistep carcinogenesis became experimentally approachable since the identification and characterization in tumor cells of altered or activated versions of cellular genes (oncogenes) that normally control cell growth and differentiation. The activating mutations confer new properties to the oncogene products and should therefore be considered as gain of function mutations. In addition, the oncogenes appear to act as dominant genetic traits since they act also in the presence of the homologous wild-type allele. However, the concept of a dominance of the transformed phenotype has been challenged by early experiments with somatic cell hybrids which showed that the fusion of normal and malignant cells may suppress the tumorigenic phenotype. The suppression or reversion of the malignant phenotype by the introduction of a normal chromosome into a tumor cell line has lent support to the idea that a family of cellular genes are coding for factors capable to interact with the cell-growth control machinery. These genes seem to reconstitute the normal control of cell growth even in the presence of an activated oncogene. In addition, a two-mutation model has been proposed to explain the epidemiological and clinical features of childhood cancers. According to the model, the development of these malignancies can be caused by the loss or inactivation of both alleles of cellular genes, as suggested by the somatic cell hybrid experiments where the function of the inactivated genes is restored by the contribution of those derived from the normal parental cells. This family of genes is designated as onco-suppressor genes since their product is necessary for the normal regulated cell growth and is lacking or inactivated in malignant cells. At gene level they should be considered as recessive genetic traits, since the tumor phenotype appears when both alleles of an oncosuppressor gene are inactivated. The mutations affecting their normal functions belong to the type « loss of function ». The molecular analysis of retinoblastoma has led to the cloning and sequencing of the related onco-suppressor gene (RB gene) whose product displays the features of a gene-regulatory protein. In addition, a binding between the RB product and various viral onco-proteins (E1A, large T, E7) has been demonstrated, thus suggesting a mechanism of RB inactivation by which some DNA viruses can transform the host cell. Finally, the increasing availability of DNA markers, defining restriction fragment length polymorphisms, has led to the mapping of the loci of inherited predisposition for familial cancer syndromes such as MEN-1, VHL and NF-2 and to the extension to common cancers of the allele losses analysis that can reveal onco-suppressor gene inactivation. This indirect approach has suggested the occurrence of different onco-suppressor genes for sporadic breast, colonic and lung cancers, bladder carcinoma, germinal tumors of the testis and malignant melanoma. In particular, colonic cancer provides a significant example of a possible multistep scenario for carcinogenesis in humans in which activated oncogenes (e.g. ras) and inactivated putative onco-suppressor genes (on chromosome 17 and 18) coexist in the same cell.

Taking Stock of Retinal Gene Therapy: Looking Back and Moving Forward

Over the past 20 years, there has been tremendous progress in retinal gene therapy. The safety and efficacy results in one early-onset severe blinding disease may lead to the first gene therapy drug approval in the United States. Here, we review how far the field has come over the past two decades and speculate on the directions that the field will take in the future.

Sarcomas in hereditary retinoblastoma

Children diagnosed with the hereditary form of retinoblastoma (Rb), a rare eye cancer caused by a germline mutation in the RB1 tumor suppressor gene, have excellent survival, but face an increased risk of bone and soft tissue sarcomas. This predisposition to sarcomas has been attributed to genetic susceptibility due to inactivation of the RB1 gene as well as past radiotherapy for Rb. The majority of bone and soft tissue sarcomas among hereditary Rb survivors occur in the head, within the radiation field, but they also occur outside the radiation field. Sarcomas account for almost half of the second primary cancers in hereditary Rb survivors, but they are very rare following non-hereditary Rb. Sarcomas among hereditary Rb survivors arise at ages similar to the pattern of occurrence in the general population. There has been a trend over the past two decades to replace radiotherapy with chemotherapy and other focal therapies (laser or cryosurgery), and most recently, chemosurgery in order to reduce the incidence of sarcomas and other second cancers in Rb survivors. Given the excellent survival of most Rb patients treated in the past, it is important for survivors, their families and health care providers to be aware of the heightened risk for sarcomas in hereditary patients.

Chromosome instability and deregulated proliferation: an unavoidable duo

The concept that aneuploidy is a characteristic of malignant cells has long been known; however, the idea that aneuploidy is an active contributor to tumorigenesis, as opposed to being an associated phenotype, is more recent in its evolution. At the same time, we are seeing the emergence of novel roles for tumor suppressor genes and oncogenes in genome stability. These include the adenomatous polyposis coli gene (APC), p53, the retinoblastoma susceptibility gene (RB1), and Ras. Originally, many of these genes were thought to be tumor suppressive or oncogenic solely because of their role in proliferative control. Because of the frequency with which they are disrupted in cancer, chromosome instability caused by their dysfunction may be more central to tumorigenesis than previously thought. Therefore, this review will highlight how the proper function of cell cycle regulatory genes contributes to the maintenance of genome stability, and how their mutation in cancer obligatorily connects proliferation and chromosome instability.

Sinonasal adenocarcinoma: a rare second malignancy in long term retinoblastoma survivors

Retinoblastoma is the most common primary cancer of the eye in children. The incidence of second tumors in survivors of bilateral retinoblastoma and in survivors of unilateral retinoblastoma who presumably carry a germline RB1 mutation is documented. This article describes the previously unrecognized association of sinonasal adenocarcinoma as a second malignancy in retinoblastoma survivors. We present three cases who received radiation therapy as a part of their treatment and developed sinonasal adenocarcinoma as a second malignancy. Sinonasal adenocarcinoma should be considered as a second malignancy in retinoblastoma survivors who present with vague sinus symptoms.

Toxicogenomics of nanoparticulate delivery of etoposide: potential impact on nanotechnology in retinoblastoma therapy

To develop a suitable formulation with high entrapment efficiency, etoposide-loaded poly(lactide-co-glycolide) nanoparticles (NPs) were formulated by single emulsion-solvent evaporation method by changing different formulation parameters such as drug loading, choice of organic solvent and percentage of emulsifier polyvinyl alcohol. The NPs showed higher entrapment efficiency, ~86% (with 15% (w/w) drug loading). The physicochemical parameters revealed smooth topology with size range (240–320 nm), a negative zeta potential (~19 mV) and in vitro sustained-release activity (~60% drug release in 40 days). Greater anti-proliferative activity ~100 times was observed with NPs (IC₅₀ = 0.002 μg/ml) than that of native etoposide (IC₅₀ = 0.2 μg/ml) in retinoblastoma cell line (Y-79). These NPs demonstrated greater (G1/S) blocking and decreased mitochondrial membrane potential as measured by flow cytometry. There was upregulation of apoptotic gene activity in NPs than native etoposide, as revealed through microarray analysis. However, this is the first ever report demonstrating the intricate modulation of genetic network affected by NPs. Collectively, these results suggest that etoposide-loaded NPs could be potentially useful as a novel drug delivery system for retinoblastoma in the future.

Figure

Modeling human osteosarcoma in the mouse: From bedside to bench

Osteosarcoma (OS) is the most common primary tumour of bone, occurring predominantly in the second decade of life. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for patients with localized (non-metastatic) disease approaching 70%. At presentation approximately 20% of patients have metastases and almost all patients with recurrent OS have metastatic disease and cure rates for patients with metastatic or recurrent disease remain poor (<20% survival). Over the past 20 years, considerable progress has been made in the understanding of OS pathogenesis, yet these insights have not translated into substantial therapeutic advances and clinical outcomes. Further progress is essential in order to develop molecularly based therapies that target both primary lesions as well as metastatic disease. The increasing sophistication with which gene expression can be modulated in the mouse, both positively and negatively in addition to temporally, has allowed for the recent generation of more faithful OS models than have previously been available. These murine OS models can recapitulate all aspects of the disease process, from initiation and establishment to invasion and dissemination to distant sites. The development and utilisation of murine models that faithfully recapitulate human osteosarcoma, complementing existing approaches using human and canine disease, holds significant promise in furthering our understanding of the genetic basis of the disease and, more critically, in advancing pre-clinical studies aimed at the rational development and trialing of new therapeutic approaches.

Thinking about repairing thinking

The work of Sinden et al. suggests that it may be possible to produce improvement in the “highest” areas of brain function by transplanting brain tissue. What appears to be the limiting factor is not the complexity of the mental process under consideration but the discreteness of the lesion which causes the impairment and the appropriateness and accuracy of placement of the grafted tissue.

Therapeutic uses for neural grafts: Progress slowed but not abandoned

In spite of Stein and Glasier's justifiable conclusion that initial optimism concerning the immediate clinical applicability of neural transplantation was premature, there exists much experimental evidence to support the potential for incorporating this procedure into a therapeutic arsenal in the future. To realize this potential will require continued evolution of our knowledge at multiple levels of the clinical and basic neurosciences.

The structure, operation, and functionality of intracerebral grafts

The concept of structure, operation, and functionality, as they may be understood by clinicians or researchers using neural transplantation techniques, are briefly defined. Following Stein & Glasier, we emphasize that the question of whether an intracerebral graft is really functional should be addressed not only in terms of what such a graft does in a given brain structure, but also in terms of what it does at the level of the organism.

The NGF superfamily of neurotrophins: Potential treatment for Alzheimer's and Parkinson's disease

Stein & Glasier suggest embryonic neural tissue grafts as a potential treatment strategy for Alzheimer's and Parkinson's disease. As an alternative, we suggest that the family of nerve growth factor-related neurotrophins and their trk (tyrosine kinase) receptors underlie cholinergic basal forebrain (CBF) and dopaminergic substantia nigra neuron degeneration in these diseases, respectively. Therefore, treatment approaches for these disorders could utilize neurotrophins.

Some practical and theoretical issues concerning fetal brain tissue grafts as therapy for brain dysfunctions

Grafts of embryonic neural tissue into the brains of adult patients are currently being used to treat Parkinson's disease and are under serious consideration as therapy for a variety of other degenerative and traumatic disorders. This target article evaluates the use of transplants to promote recovery from brain injury and highlights the kinds of questions and problems that must be addressed before this form of therapy is routinely applied. It has been argued that neural transplantation can promote functional recovery through the replacement of damaged nerve cells, the reestablishment of specific nerve pathways lost as a result of injury, the release of specific neurotransmitters, or the production of factors that promote neuronal growth. The latter two mechanisms, which need not rely on anatomical connections to the host brain, are open to examination for nonsurgical, less intrusive therapeutic use. Certain subjective judgments used to select patients who will receive grafts and in assessment of the outcome of graft therapy make it difficult to evaluate the procedure. In addition, little long-term assessment of transplant efficacy and effect has been done in nonhuman primates. Carefully controlled human studies, with multiple testing paradigms, are also needed to establish the efficacy of transplant therapy.

Models of neurological defects and defects in neurological models

The transition from research to patient following advances in transplantation research is likely to be disappointing unless it includes a better understanding of critically relevant characteristics of the neurological disorder and improvements in the animal models, particularly the behavioral features. The appropriateness of the model has less to do with the species than with how the species is used.

Recurrent focal copy-number changes and loss of heterozygosity implicate two noncoding RNAs and one tumor suppressor gene at chromosome 3q13.31 in osteosarcoma

Osteosarcomas are copy number alteration (CNA)-rich malignant bone tumors. Using microarrays, fluorescence in situ hybridization, and quantitative PCR, we characterize a focal region of chr3q13.31 (osteo3q13.31) harboring CNAs in 80% of osteosarcomas. As such, osteo3q13.31 is the most altered region in osteosarcoma and contests the view that CNAs in osteosarcoma are nonrecurrent. Most (67%) osteo3q13.31 CNAs are deletions, with 75% of these monoallelic and frequently accompanied by loss of heterozygosity (LOH) in flanking DNA. Notably, these CNAs often involve the noncoding RNAs LOC285194 and BC040587 and, in some cases, a tumor suppressor gene that encodes the limbic system-associated membrane protein (LSAMP). Ubiquitous changes occur in these genes in osteosarcoma, usually involving loss of expression. Underscoring their functional significance, expression of these genes is correlated with the presence of osteo3q13.31 CNAs. Focal osteo3q13.31 CNAs and LOH are also common in cell lines from other cancers, identifying osteo3q13.31 as a generalized candidate region for tumor suppressor genes. Osteo3q13.31 genes may function as a unit, given significant correlation in their expression despite the great genetic distances between them. In support of this notion, depleting either LSAMP or LOC285194 promoted proliferation of normal osteoblasts by regulation of apoptotic and cell-cycle transcripts and also VEGF receptor 1. Moreover, genetic deletions of LOC285194 or BC040587 were also associated with poor survival of osteosarcoma patients. Our findings identify osteo3q13.31 as a novel region of cooperatively acting tumor suppressor genes.

The cyclin-dependent kinase inhibitors, cki-1 and cki-2, act in overlapping but distinct pathways to control cell cycle quiescence during C. elegans development

Cyclin-dependent kinase inhibitors (CKIs) are major contributors to the decision to enter or exit the cell cycle. The Caenorhabditis elegans genome encodes two CKIs belonging to the Cip/Kip family, cki-1 and cki-2. cki-1 has been shown to act as a canonical negative regulator of cell cycle entry, while the role of cki-2 remains unclear. We identified cki-2 in a genome-wide RNAi screen to reveal genes essential for developmental cell cycle quiescence. Examination of cki-2 knockout animals revealed extra rounds of cell divisions, verifying a role in establishing or maintaining the temporary cell cycle arrest. Despite the overlapping defects, the pathways mediated by cki-1 and cki-2 are discrete since the extra cell phenotype conferred by a putative cki-2(null) mutation is enhanced upon additional loss of cki-1 activity. Moreover, the extra cell division defect of cki-2 is not increased with the additional loss of lin-35 Rb, as is seen with cki-1. Thus, both cki-1 and cki-2 mediate cell cycle quiescence, but our genetic and phenotypic analyses demonstrate that they act within distinct pathways to exert control over the cell cycle machinery.

How the Rb tumor suppressor structure and function was revealed by the study of Adenovirus and SV40

The review recounts the history of how the study of the DNA tumor viruses including polyoma, SV40 and Adenovirus brought key insights into the structure and function of the Retinoblastoma protein (Rb). Knudsen's model of the two-hit hypothesis to explain patterns of hereditary and sporadic retinoblastoma provided the foundation for the tumor suppressor hypothesis that ultimately led to the cloning of the Rb gene. The discovery that SV40 and Adenovirus could cause tumors when inoculated into animals was startling not only because SV40 had contaminated the poliovirus vaccine and Adenovirus was a common cause of viral induced pneumonia but also because they provided an opportunity to study the genetics and biochemistry of cancer. Studies of mutant forms of these viruses led to the identification of the E1A and Large T antigen (LT) oncogenes and their small transforming elements including the Adenovirus Conserved Regions (CR), the SV40 J domain and the LxCxE motif. The immunoprecipitation studies that initially revealed the size and ultimately the identity of cellular proteins that could bind to these transforming elements were enabled by the widespread development of highly specific monoclonal antibodies against E1A and LT. The identification of Rb as an E1A and LT interacting protein quickly led to the cloning of p107, p130, p300, CBP, p400 and TRRAP and the concept that viral transformation was due, at least in part, to the perturbation of the function of normal cellular proteins. In addition, studies on the ability of E1A to transactivate the Adenovirus E2 promoter led to the cloning of the heterodimeric E2F and DP transcription factor and recognition that Rb repressed transcription of cellular genes required for cell cycle entry and progression. More recent studies have revealed how E1A and LT combine the activity of Rb and the other cellular associated proteins to perturb expression of many genes during viral infection and tumor formation.

Somatic mutations affect key pathways in lung adenocarcinoma

Determining the genetic basis of cancer requires comprehensive analyses of large collections of histopathologically well-classified primary tumours. Here we report the results of a collaborative study to discover somatic mutations in 188 human lung adenocarcinomas. DNA sequencing of 623 genes with known or potential relationships to cancer revealed more than 1,000 somatic mutations across the samples. Our analysis identified 26 genes that are mutated at significantly high frequencies and thus are probably involved in carcinogenesis. The frequently mutated genes include tyrosine kinases, among them the EGFR homologue ERBB4; multiple ephrin receptor genes, notably EPHA3; vascular endothelial growth factor receptor KDR; and NTRK genes. These data provide evidence of somatic mutations in primary lung adenocarcinoma for several tumour suppressor genes involved in other cancers--including NF1, APC, RB1 and ATM--and for sequence changes in PTPRD as well as the frequently deleted gene LRP1B. The observed mutational profiles correlate with clinical features, smoking status and DNA repair defects. These results are reinforced by data integration including single nucleotide polymorphism array and gene expression array. Our findings shed further light on several important signalling pathways involved in lung adenocarcinoma, and suggest new molecular targets for treatment.

Understanding the development of human bladder cancer by using a whole-organ genomic mapping strategy

The search for the genomic sequences involved in human cancers can be greatly facilitated by maps of genomic imbalances identifying the involved chromosomal regions, particularly those that participate in the development of occult preneoplastic conditions that progress to clinically aggressive invasive cancer. The integration of such regions with human genome sequence variation may provide valuable clues about their overall structure and gene content. By extension, such knowledge may help us understand the underlying genetic components involved in the initiation and progression of these cancers. We describe the development of a genome-wide map of human bladder cancer that tracks its progression from in situ precursor conditions to invasive disease. Testing for allelic losses using a genome-wide panel of 787 microsatellite markers was performed on multiple DNA samples, extracted from the entire mucosal surface of the bladder and corresponding to normal urothelium, in situ preneoplastic lesions, and invasive carcinoma. Using this approach, we matched the clonal allelic losses in distinct chromosomal regions to specific phases of bladder neoplasia and produced a detailed genetic map of bladder cancer development. These analyses revealed three major waves of genetic changes associated with growth advantages of successive clones and reflecting a stepwise conversion of normal urothelial cells into cancer cells. The genetic changes map to six regions at 3q22-q24, 5q22-q31, 9q21-q22, 10q26, 13q14, and 17p13, which may represent critical hits driving the development of bladder cancer. Finally, we performed high-resolution mapping using single nucleotide polymorphism markers within one region on chromosome 13q14, containing the model tumor suppressor gene RB1, and defined a minimal deleted region associated with clonal expansion of in situ neoplasia. These analyses provided new insights on the involvement of several non-coding sequences mapping to the region and identified novel target genes, termed forerunner (FR) genes, involved in early phases of cancer development.

Localization in man of fifteen DNA sequences within the chromosome segment 13q12-q22

Fifteen human chromosome 13 specific DNA fragments, isolated from a lambda phage genomic library, were localized within the segment 13q12-q22. One was mapped to 13q12.1-q12.2, three to 13q12.3-q13.1, one to 13q14,1-q14.2, five to 13q14.1-q21.1, one to 13q21.1-q21.2, two to 13q21.2, and one to 13q22.1, and one to 13q22. The localization was performed by hybridization to Southern blots of a panel of human cell lines with overlapping deletions in 13q, and for three probes also by in situ hybridization to metaphase chromosomes.

Epidemiology of genetically determined cancer

Dominantly heritable susceptibility is known for virtually every cancer. Susceptibility is typically restricted to one or a few tumours. For some tumours there appear to be at least two different predisposing conditions. Some mutant gene carriers survive to old age without developing the expected tumour(s). Some cases are new germline mutations. None of the conditions is very common, because of natural selection against gene carriers. Two questions arise: What is inherited? What is the relationship between the hereditary and non-hereditary forms of the same tumour? Retinoblastoma is a prototypic tumour. Penetrance in humans is nearly complete by the age of five years in the heritable form, which usually affects both eyes. Rare cases in which there is a constitutional deletion of chromosomal band 13q14 permitted localization of the responsible gene. Tumour formation is clearly a rare event at the cellular level, suggesting the necessity of a second, somatic, event. The difference in ages at diagnosis between unilateral and bilateral cases also suggests that two somatic events occur in non-hereditary cases. One explanation is that the gene is recessive and the second event involves loss of the remaining normal allele by mutation, non-disjunction, deletion or somatic recombination. The normal allele may be regarded as anti-oncogenic.

Zebrafish dou yan mutation causes patterning defects and extensive cell death in the retina

The size of an organ is largely determined by the number of cells it contains, which in turn is regulated by two opposing processes, cell proliferation and cell death, however, it is generally not clear how cell proliferation and cell death are coordinated during development. Here, we characterize the zebrafish dou yan(mi234) mutation that results in a dramatic reduction of retinal size and a disruption of retinal differentiation and lamination. The retinal size reduction is caused by increased retinal cell death in a non-cell-autonomous manner during early development. The phenotypic defect in dou yan(mi234) arises coincident with the onset of retinal neurogenesis and differentiation. Interestingly, unlike many other small eye mutations, the mutation does not increase the level of cell death in the brain, suggesting that the brain and retina use different mechanisms to maintain cell survival. Identification and further study of the dou yan gene will enhance our understanding of the molecular mechanisms regulating retinal cellular homeostasis, i.e., the balance between cell proliferation and cell death.

CHD5 is a tumor suppressor at human 1p36

Cancer gene discovery has relied extensively on analyzing tumors for gains and losses to reveal the location of oncogenes and tumor suppressor genes, respectively. Deletions of 1p36 are extremely common genetic lesions in human cancer, occurring in malignancies of epithelial, neural, and hematopoietic origin. Although this suggests that 1p36 harbors a gene that drives tumorigenesis when inactivated, the identity of this tumor suppressor has remained elusive. Here we use chromosome engineering to generate mouse models with gain and loss of a region corresponding to human 1p36. This approach functionally identifies chromodomain helicase DNA binding domain 5 (Chd5) as a tumor suppressor that controls proliferation, apoptosis, and senescence via the p19(Arf)/p53 pathway. We demonstrate that Chd5 functions as a tumor suppressor in vivo and implicate deletion of CHD5 in human cancer. Identification of this tumor suppressor provides new avenues for exploring innovative clinical interventions for cancer.

Risk of soft tissue sarcomas by individual subtype in survivors of hereditary retinoblastoma

BACKGROUND

Survivors of hereditary retinoblastoma have an increased risk for second malignancies, especially soft tissue sarcomas. However, the risks of individual histologic subtypes of soft tissue sarcomas have not been evaluated.

METHODS

We estimated the risk for six subtypes of soft tissue sarcomas (fibrosarcoma, liposarcoma, histiocytoma, leiomyosarcoma, rhabdomyosarcoma, and others) in a cohort of 963 one-year survivors of hereditary retinoblastoma among patients diagnosed at two US institutions from 1914 through 1984. We calculated standardized incidence ratios (SIRs) for specific subtypes of soft tissue sarcomas by comparison with population data from the Connecticut Tumor Registry or from National Cancer Institute Surveillance, Epidemiology, and End Results database. We also calculated the cumulative risk for all soft tissue sarcomas combined.

RESULTS

We observed 69 soft tissue sarcomas in 68 patients with hereditary retinoblastoma. Risks were elevated for soft tissue sarcomas overall (SIR = 184, 95% confidence interval [CI] = 143 to 233) and for individual subtypes. Leiomyosarcoma was the most frequent subtype (SIR = 390, 95% CI = 247 to 585), with 78% of leiomyosarcomas diagnosed 30 or more years after the retinoblastoma diagnosis (SIR = 435, 95% CI = 258 to 687). Among patients treated with radiotherapy for retinoblastoma, we found statistically significantly increased risks of soft tissue sarcomas in the field of radiation. Irradiated patients also had increased risks of soft tissue sarcomas, especially leiomyosarcomas, outside the field of radiation, and risks of soft tissue sarcomas were increased in nonirradiated patients as well, indicating a genetic predisposition to soft tissue sarcomas independent of radiation. The cumulative risk for any soft tissue sarcoma 50 years after radiotherapy for retinoblastoma was 13.1% (95% CI = 9.7% to 17.0%).

CONCLUSION

Long-term follow-up of a cohort of survivors of hereditary retinoblastoma revealed a statistically significant excess of leiomyosarcoma and other soft tissue sarcomas that persists decades after the retinoblastoma diagnosis. Retinoblastoma survivors should undergo regular medical surveillance for sarcomas in their adult years.

Regulation of CDKN2A/B and Retinoblastoma genes in Xiphophorus melanoma

Xiphophorus interspecies hybrids provide several well-characterized genetic models of melanoma susceptibility. The Xiphophorus CDKN2A/B gene, homologous to mammalian CDKN2A/B cyclin-dependent kinase inhibitors (p16 and p15), is a candidate tumor susceptibility gene in these models. Using real-time PCR and Western blot analysis, we analyzed expression of CDKN2A/B in spontaneous and UV-induced primary melanomas from individual backcross hybrid fish. We found that CDKN2A/B mRNA is highly expressed in melanomas (18-fold), relative to other fish tissues. Expression is also elevated, to a lesser extent (9.5-fold), in melanized skin from tumor-bearing fish. However, quantitative levels of CDKN2A/B mRNA in tumors varied considerably and positively correlated with expression of the Xmrk oncogene, suggesting possible functional interaction between Xmrk and CDKN2A/B expression. As a homolog corresponding to members of the mammalian CDKN2 family which regulate cell cycle progression at the G1 checkpoint, the CDKN2A/B p13 protein is a putative regulator of the G1 checkpoint apparatus in Xiphophorus. Since CDKN2A is often observed to be inversely regulated compared to RB in some human tumors, and is capable of transcriptionally regulating RB in human ovarian tumors, we cloned the Xiphophorus maculatus RB cDNA and analyzed RB expression by real-time PCR and Western blot analysis in the fish melanomas. These experiments were designed to ascertain whether CDKN2A/B and RB expression were inversely correlated. Our results indicate that RB mRNA was consistently expressed at only a 2-fold higher level in both tumors and melanized skin than in muscle. Qualitatively similar results were obtained for protein expression. These results collectively suggest that (i) Xmrk and CDKN2A/B may be co-regulated at the transcriptional level, and (ii) there is little, if any, alteration of RB expression in Xiphophorus melanomas.

Selective requirements for E2f3 in the development and tumorigenicity of Rb-deficient chimeric tissues

The tumor suppressor function of the retinoblastoma protein pRB is largely dependent upon its capacity to inhibit the E2F transcription factors and thereby cell proliferation. Attempts to study the interplay between pRB and the E2Fs have been hampered by the prenatal death of Rb; E2f nullizygous mice. In this study, we isolated Rb; E2f3 mutant embryonic stem cells and generated Rb(-/-); E2f3(-/-) chimeric mice, thus bypassing the lethality of the Rb(-/-); E2f3(-/-) germ line mutant mice. We show that loss of E2F3 has opposing effects on two of the known developmental defects arising in Rb(-/-) chimeras; it suppresses the formation of cataracts while aggravating the retinal dysplasia. This model system also allows us to assess how E2f3 status influences tumor formation in Rb(-/-) tissues. We find that E2f3 is dispensable for the development of pRB-deficient pituitary and thyroid tumors. In contrast, E2f3 inactivation completely suppresses the pulmonary neuroendocrine hyperplasia arising in Rb(-/-) chimeric mice. This hyperproliferative state is thought to represent the preneoplastic lesion of small-cell lung carcinoma. Therefore, our observation highlights a potential role for E2F3 in the early stages of this tumor type.

Interaction of retinoblastoma protein family members with large T-antigen of primate polyomaviruses

The retinoblastoma gene product pRb and other members of the Rb family of pocket proteins have a central role in the regulation of cell cycle progression. Soon after its discovery, pRb was found to interact with the transforming oncoproteins of DNA tumor viruses and this led to rapid advances in our understanding of the mechanisms of viral transformation and cell cycle progression. DNA viruses of the polyomavirus family have small, circular, double-stranded DNA genomes contained within non-enveloped icosahedral capsids and are highly tumorigenic in experimental animals. At least three types of polyomavirus infect humans: JC virus (JCV), BK virus (BKV) and Simian Vacuolating virus-40. The early region of these viruses encodes the transforming proteins large T-antigen and small t-antigen, which are involved in viral replication and also promote transformation of cells in culture and oncogenesis in vivo. Binding of T-antigen to pRb promotes the activation of the E2F family of transcription factors, which induce the expression of cellular genes required for S phase. In the context of lytic infection, this cell cycle progression is necessary for viral replication because polyomaviruses rely on S phase-specific host factors for their DNA synthesis. In the context of cellular transformation and tumorigenesis, T-antigen/pRB interaction is an indispensable event.

Pocket protein function in melanocyte homeostasis and neoplasia

Melanoma is the most lethal of human skin cancers and its incidence is increasing worldwide [L.K. Dennis (1999). Arch. Dermatol. 135, 275; C. Garbe et al. (2000). Cancer 89, 1269]. Melanomas often metastasize early during the course of the disease and are then highly intractable to current therapeutic regimens [M.F. Demierre and G. Merlino (2004). Curr. Oncol. Rep. 6, 406]. Consequently, understanding the factors that maintain melanocyte homeostasis and prevent their neoplastic transformation into melanoma is of utmost interest from the perspective of therapeutic interdiction. This review will focus on the role of the pocket proteins (PPs), Rb1 (retinoblastoma protein), retinoblastoma-like 1 (Rbl1 also known as p107) and retinoblastoma-like 2 (Rbl2 also known as p130), in melanocyte homeostasis, with particular emphasis on their functions in the cell cycle and the DNA damage repair response. The potential mechanisms of PP deregulation in melanoma and the possibility of PP-independent pathways to melanoma development will also be considered. Finally, the role of the PP family in ultraviolet radiation (UVR)-induced melanoma and the precise contribution that each PP family member makes to melanocyte homeostasis will be discussed in the context of a number of genetically engineered mouse models.

Melanocytes in conditional Rb-/- mice are normal in vivo but exhibit proliferation and pigmentation defects in vitro

The function of the retinoblastoma tumour suppressor (Rb1), and the pocket protein family in general, has been implicated as an important focal point for deregulation in many of the molecular pathways mutated in melanoma. We have focused on the role of Rb1 in mouse melanocyte homeostasis using gene targeting and Cre/loxP mediated tissue-specific deletion. We show that constitutive Cre-mediated ablation of Rb1 exon 2 prevents the production of Rb1 and recapitulates the phenotype encountered in other Rb1 knockout mouse models. Mice with conditional melanocyte-specific ablation of Rb1 manifest overtly normal pigmentation and are bereft of melanocytic hyperproliferative defects or apoptosis-induced depigmentation. Histologically, these mice have melanocyte morphology and distribution comparable with control littermates. In contrast, Rb1-null melanocytes removed from their in vivo micro-environment and cultured in vitro display some of the characteristics associated with a transformed phenotype. They proliferate at a heightened rate when compared with control melanocytes and have a decreased requirement for mitogens. With progressive culture the cells depigment at relatively early passage and display a gross morphology which, whilst reminiscent of early passage melanocytes, is generally different to equivalent passage control cells. These results indicate that Rb1 is dispensable for in vivo melanocyte homeostasis when its ablation is targeted from the melanoblast stage onwards, however, when cultured in vitro, Rb1 loss increases melanocyte growth but the cells are not fully transformed.

The retinoblastoma gene family in cell cycle regulation and suppression of tumorigenesis

Since its discovery in 1986, as the first tumor suppressor gene, the retinoblastoma gene (Rb) has been extensively studied. Numerous biochemical and genetic studies have elucidated in great detail the function of the Rb gene and placed it at the heart of the molecular machinery controlling the cell cycle. As more insight was gained into the genetic events required for oncogenic transformation, it became clear that the retinoblastoma gene is connected to biochemical pathways that are dysfunctional in virtually all tumor types. Besides regulating the E2F transcription factors, pRb is involved in numerous biological processes such as apoptosis, DNA repair, chromatin modification, and differentiation. Further complexity was added to the system with the discovery of p107 and p130, two close homologs of Rb. Although the three family members share similar functions, it is becoming clear that these proteins also have unique functions in differentiation and regulation of transcription. In contrast to Rb, p107 and p130 are rarely found inactivated in human tumors. Yet, evidence is accumulating that these proteins are part of a "tumor-surveillance" mechanism and can suppress tumorigenesis. Here we provide an overview of the knowledge obtained from studies involving the retinoblastoma gene family with particular focus on its role in suppressing tumorigenesis.

Abnormalities of the RB1 pathway in ovarian serous papillary carcinoma as determined by overexpression of the p16(INK4A) protein

Dysfunction of proteins involved in the G1 to S transition of the cell cycle, such as p16(INK4A) and RB1, is common in many cancer types. A screen of p16 protein expression was performed in benign, borderline, and invasive ovarian tumors, together with endometrial cancers, aligned on a tissue microarray. We observed frequent p16 overexpression in serous papillary carcinomas of ovarian and endometrial origin. An extended cohort of ovarian serous papillary carcinomas was examined to further evaluate the frequency of p16 overexpression. Strong, uniform staining in the majority of cancer cells occurred commonly in invasive serous papillary ovarian cancers, particularly in grade 3 carcinomas. RB1 protein expression abnormalities were rare. Our data indicate that abnormalities in the retinoblastoma pathway, as determined by p16 overexpression, are common in serous papillary carcinomas and are probably an early event.

Rb/E2F: a two-edged sword in the melanocytic system

Rb is a tumor suppressor that represses the expression of E2F regulated genes required for cell cycle progression. It is inactivated in melanomas and other cancer cells by phosphorylation catalyzed by persistent cyclin dependent kinase (CDK) activity. CDK activity is sustained in melanoma cells mostly by the elimination of the CDK inhibitor p16INK4A and by high levels of cyclins whose expression is maintained by stimuli emanating from activated cell surface receptors and/or mutated intracellular intermediates, such as N-Ras and B-Raf. However, Rb also suppresses the expression of apoptosis genes, and its presence protects normal melanocytes from cell death. Its high expression in human melanoma cells and tumors suggests a similar role in malignant cells as well. The differential release and suppression of E2F transcriptional activity is likely to depend on promoter-specific E2F/Rb interaction. Phosphorylated Rb is displaced from cell cycle genes but not from others. In addition, Rb gene repression is dependent on the nature of Rb-E2F interaction and the activity of the Rb-bound proteins recruited to the promoter. Deciphering the differences in Rb/E2F complex formation in normal and malignant melanocytes is likely to shed light on the mechanism by which Rb can exert tumor suppressing and promoting activities in this cellular system. The Rb/E2F pathway provides opportunities for efficient therapy at multiple levels. Novel drugs can reactivate Rb potential to suppress growth cycle promoting genes. In addition, the high E2F transcriptional activity in melanoma cells can be exploited to deliver cytotoxic molecules specifically to tumors, sparing the normal tissues.

Tissue-specific tumor suppressor activity of retinoblastoma gene homologs p107 and p130

The retinoblastoma gene family consists of three genes: RB, p107, and p130. While loss of pRB causes retinoblastoma in humans and pituitary gland tumors in mice, tumorigenesis in other tissues may be suppressed by p107 and p130. To test this hypothesis, we have generated chimeric mice from embryonic stem cells carrying compound loss-of-function mutations in the Rb gene family. We found that Rb/p107- and Rb/p130-deficient mice were highly cancer prone. We conclude that in a variety of tissues tumor development by loss of pRB is suppressed by its homologs p107 and p130. The redundancy of the retinoblastoma proteins in vivo is reflected by the behavior of Rb-family-defective mouse embryonic fibroblasts in vitro.

Analysis of chromosome abnormalities by comparative genomic hybridization in malignant peripheral primitive neuroectodermal tumor of the ovary

OBJECTIVE

Malignant primitive neuroectodermal tumor (PNET) originating from the ovary rather than from the central nervous system is extremely rare. The aim of this study is to demonstrate the chromosomal abnormalities in a case of peripheral primitive neuroectodermal tumor (PPNET) arising from the ovary of a girl.

METHODS

The 13-year-old girl underwent exploratory laparotomy because of a huge pelvic tumor in lower abdomen and pelvis. She underwent removal of ovaries, tubes, omentum, peritoneal nodules, and portion of urinary bladder. Tumor specimens were sent for pathology, short-term tissue culture, and for storage in deep freezer for laboratory studies. Immunohistochemical stainings of the tumor with antibodies against O-13 (MIC/CD99), NSE, GFAP, S-100, cytokeratin AE1/AE3, desmin, NF, and AFP were performed. Short-term cell culture of fresh tumor was done for analysis of chromosomal aberrations by the technique of comparative genomic hybridization (CGH). Names of specific genes corresponding to the losses or gains on gene map loci were identified from OMIM (Online Mendelian Inheritance in Man) of the NCBI website,. The overexpressions of N-myc and EGFR as well as underexpressions of Rb and ARHI were detected by RT-PCR analysis. The patient expired 17 months later despite of chemotherapy, repeated surgery, and radiation therapy.

RESULT

The histopathology of the specimens revealed malignant neuroectodermal tumor, involving ovaries, tubes, bladder, omentum, and peritoneum. Immunohistochemical stainings of PPNET of the ovary showed positive reaction for O-13 (MIC2/CD99) and NSE, but negative for GFAP, S-100, cytokeratin AE1/AE3, desmin, NF, and AFP. Analysis of CGH revealed multiple chromosomal abnormalities including losses of chromosomes in 1p, 1q, 4q, 6p, 6q, 7q, 8q, 13q, and 19q; as well as gains of chromosomes in 1q, 2p, 7p, 9q, 18q, and Xq. Losses of 13q14.1-q14.2, 1p31, and 4q34-q35 indicated that Rb gene, ARHI, and FAT were deleted. Gains of 2p24.1, 1q23, and 7p12.3-p12.1 demonstrated that N-myc oncogene, FASL, GITRL, and EGFR were amplified. RT-PCR analysis showed that N-myc and EGFR were overexpressed, while Rb and ARHI were underexpressed.

CONCLUSIONS

This report is the first to show multiple chromosomal aberrations in PPENT arising from the ovary. The deletions of Rb, ARHI, and FAT, as well as amplification of N-myc, FASL, GITRL, and EGFR, may be the crucial factors for tumorigenesis and the aggressive biological behavior of PPNET.

Cancer in Fanconi anemia, 1927-2001

BACKGROUND

Fanconi anemia (FA) is an autosomal recessive disease associated with an abnormal response to DNA damage. Although FA is well known for the association of aplastic anemia and characteristic birth defects, leukemia and solid tumors also occur at a high rate in this group of patients. A review of all reported cases is informative with regard to the specific types of cancer, the ages at which they occur, and the cumulative probability of their development.

METHODS

Medline and bibliographies of publications were searched for articles containing "Fanconi's anemia" or "aplastic anemia" and all cases of FA from 1927 through 2001 were included in the database. Cancer cases were identified within these reports. Descriptive statistical analyses were performed using Stata7 software.

RESULTS

One thousand three hundred cases of FA were identified. Nine percent had leukemia (primarily acute myeloid leukemia), 7% had myelodysplastic syndrome, 5% had solid tumors, and 3% had liver tumors. Patients with cancer were older than the cancer-free patients at the time of diagnosis of FA. The median age for cancer (including leukemia) was 16, compared with 68 in the general population. The most frequent solid tumors were aerodigestive and gynecological carcinomas. In approximately 25% of patients with cancer, the malignancy preceded the diagnosis of FA.

CONCLUSIONS

If the competing risks of aplastic anemia and leukemia could be removed, the estimated cumulative probability of development of a solid tumor in FA patients is 76% by the age of 45 years. Carcinogenic pathways and cancer prevention, surveillance, and treatment can be studied to advantage in this genetic model of human cancer.

The role of retinoblastoma protein family in the control of germ cell proliferation, differentiation and survival

Retinoblastoma family proteins pRb, p107 and p130 are differentially expressed in the rat testis. They function in specific cell types during testicular development and spermatogenesis, participating in the control of proliferation, differentiation, and survival. Their expression levels and phosphorylation status are modulated during germ cell cycle progression and apoptosis. Hyperphosphorylated states and elevated levels of p107 are correlated with cell cycle progression, whereas hypophosphorylated states and reduced levels are associated with suppression of proliferation and apoptosis in germ cells and Leydig cells. These proteins may also serve as markers of cell cycle status of germ cells during spermatogenesis.

Changes in retinoblastoma gene expression during cervical cancer progression

The role of tumour suppressor genes in the development of human cancers has been studied extensively. In viral carcinogenesis, the inactivation of suppressor proteins such as retinoblastoma (pRb) and p53, and cellular oncogenes overexpression, such as c-myc, has been the subject of a number of investigations. In uterine-cervix carcinomas, where high-risk human papillomavirus (HPV) plays an important role, pRb and p53 are inactivated by E7 and E6 viral oncoproteins, respectively. However, little is known about the in situ expression of some of these proteins in pre-malignant and malignant cervical tissues. On the other hand, it has also been demonstrated that c-myc is involved in cervical carcinogenesis, and that pRb participates in the control of c-myc gene expression. By using immunostaining techniques, we investigated pRb immunodetection pattern in normal tissues, squamous intraepithelial lesions (SILs) and invasive carcinomas from the uterine cervix. Our data show low pRb detection in both normal cervical tissue and invasive lesions, but a higher expression in SILs. C-Myc protein was observed in most of the cellular nuclei of the invasive lesions, while in SILs was low. These findings indicate a heterogeneous pRb immunostaining during the different stages of cervical carcinogenesis, and suggest that this staining pattern could be a common feature implicated in the pathogenesis of uterine-cervix carcinoma.

Loss of heterozygosity at the RB-1 locus and pRB immunostaining in epithelial ovarian tumors: a molecular, immunohistochemical, and clinicopathologic study

Alterations in the retinoblastoma gene (RB-1) are common in human neoplasia. The frequency of loss of heterozygosity (LOH) at the RB-1 locus on chromosome 13q14 was studied in a series of 51 epithelial ovarian tumors (10 benign, 7 borderline, and 34 malignant). LOH was scored by the absence or reduction of the signal to < 50% of one of the alleles in tumor DNA compared with normal DNA. LOH results were correlated with retinoblastoma protein (pRB) immunostaining. LOH at the RB-1 locus was observed in 9 tumors (17.6%), specifically in 1 of 7 borderline tumors and 8 of 34 ovarian carcinomas (23.5%). Among the malignant tumors, LOH occurred more frequently in carcinomas with serous differentiation (7/23; 30%). A heterogeneous (10% to 70% cells) or diffuse (> 70% cells) pRB immunostaining was less frequent in benign (1/10; 10%) and borderline (2/7; 28%) tumors than in ovarian carcinomas (15/34; 44%), an observation that correlated with the higher proliferative index in carcinomas than in benign and borderline tumors. However, lack or only focal (< 10% cells) pRB immunostaining occurred in the vast majority of tumors with LOH at the RB-1 locus (7/9; 77%), a finding that may suggest a tumor suppressor role for RB-1 in these tumors. The results suggest that RB-1 may play a role in a subset of ovarian carcinomas, particularly those exhibiting serous differentiation.