Cytogenetic studies of epithelial ovarian carcinoma

Bilateral ovarian carcinomas differ in the expression of metastasis-related genes

The mechanisms behind bilaterality of ovarian carcinomas are not fully understood, as the two tumors could possibly represent two primary tumors, a primary tumor and a metastasis, or two metastases. The gene expression profiles from bilateral high-grade serous carcinomas (HGSCs) and clear cell carcinomas (CCCs) of the ovary were compared to study the association between the tumors of the two sides. A separate analysis of genes from chromosome 19 was also performed, since this chromosome is frequently rearranged in ovarian carcinomas. Tumors from four patients were included (three pairs of HGSC and one pair of CCC). The gene expression was analyzed at the exon level, and bilateral tumors were compared to identify within-pair differences. Gene expression data were also compared with genomic information on the same tumors. Similarities in gene expression were observed between the tumors within each pair, as expected if the two tumors were clonally related. However, certain genes exhibited differences in expression between the two sides, indicating metastasis involvement. Among the most differently expressed genes, one gene was common to all four pairs: Immunoglobulin J. In all HGSC pairs, serpin peptidase inhibitor, clade B (ovalbumin), member 2, serpin family E member 1 and phospholipase A2, group IIA (platelets, synovial fluid) were also among the differentially expressed genes. The specific analysis of chromosome 19 highlighted expression differences in the zinc finger protein 36 gene. These results indicate that bilateral ovarian tumors represent different stages during progression of a single clonal process. Several of the genes observed to be differently expressed are known to be metastasis-related, and are likely to be also involved in spreading from one side to the other in the bilateral cancer cases examined.

Genomic profile of ovarian carcinomas

Background

It is known that all tumors studied in sufficient number to draw conclusions show characteristic/specific chromosomal rearrangements, and the identification of these chromosomes and the genes rearranged behind the aberrations may ultimately lead to a tailor-made therapy for each cancer patient. Knowledge about the acquired genomic aberrations of ovarian carcinomas is still unsatisfactory.

Methods

We cytogenetically analyzed 110 new cases of ovarian carcinoma of different histological subtypes using karyotyping of G-banded chromosomes and high-resolution comparative genomic hybridization. We first compared the aberration patterns identified by the two genomic screening techniques using the so-called “classical” pathological classification in which the carcinomas are grouped as tumors of types I and II. We also broke down our findings according to the more “modern” classification which groups the carcinomas in five different categories.

Results

The chromosomal breakpoints identified by karyotyping tended to cluster to 19p/q and to 11q, but no unquestionably recurrent rearrangement could be seen. Common imbalances were scored as gains from 1q, 3q, 7q, and 8q and losses from 17p, 19q, and 22q. Gain of material from 8q23 and losses from 19q and 22q have previously been described at high frequencies in bilateral and borderline ovarian carcinomas. The fact that they were present both in “precursor” lesions, i.e., borderline tumors, as well as in tumors of more advanced stages, i.e., carcinomas, highlights the possibility of an adenoma-carcinoma sequence in ovarian carcinogenesis.

Conclusion

Based on the relatively simple genomic changes we identified in the low-grade serous carcinomas examined (n = 7) and which largely corresponded to the aberration pattern formerly identified in borderline tumors, one can interpret the cytogenetic data as supporting the view that the low-grade carcinomas represent a phenotypically more advanced stage of borderline tumors. Whether transition from low-grade to high-grade carcinoma also occurs, is a question about which the genomic data is still inconclusive.

Chromosome 19 rearrangements in ovarian carcinomas: zinc finger genes are particularly targeted

Chromosome 19 is frequently rearranged in ovarian carcinomas, but the pathogenetic consequences of this are not clearly understood. We performed microarray gene expression analysis on 12 ovarian carcinomas that carry a rearranged chromosome 19 in their karyotype. These aberrant chromosomes have previously been microdissected and analyzed by array-based CGH. In the current study, we wanted to explore whether the genomic alterations thus detected correlated with changes in gene expression. The microarray gene expression analysis gave information on 407 genes mapping in gained genomic regions on chromosome 19, of which 92 showed association between DNA gain and upregulated expression. Of the genes showing this association, 39 (42%) showed gain in at least two samples. The majority of these 39 genes of interest (n = 24, 62%) encode zinc finger proteins, which otherwise make up only 15% of the approximately 1,400 genes on chromosome 19. The strongest association was found for ZNF223 which was upregulated in samples with genomic gain compared with samples without gain. We suggest that DNA copy number changes brought about by rearrangements of chromosome 19 contribute to ovarian carcinogenesis by leading to upregulation of ZNF223 and other zinc finger genes. © 2014 Wiley Periodicals, Inc.

Genomic aberrations in borderline ovarian tumors

Background

According to the scientific literature, less than 30 borderline ovarian tumors have been karyotyped and less than 100 analyzed for genomic imbalances by CGH.

Methods

We report a series of borderline ovarian tumors (n = 23) analyzed by G-banding and karyotyping as well as high resolution CGH; in addition, the tumors were analyzed for microsatellite stability status and by FISH for possible 6q deletion.

Results

All informative tumors were microsatellite stable and none had a deletion in 6q27. All cases with an abnormal karyotype had simple chromosomal aberrations with +7 and +12 as the most common. In three tumors with single structural rearrangements, a common breakpoint in 3q13 was detected. The major copy number changes detected in the borderline tumors were gains from chromosome arms 2q, 6q, 8q, 9p, and 13q and losses from 1p, 12q, 14q, 15q, 16p, 17p, 17q, 19p, 19q, and 22q. The series included five pairs of bilateral tumors and, in two of these pairs, informative data were obtained as to their clonal relationship. In both pairs, similarities were found between the tumors from the right and left side, strongly indicating that bilaterality had occurred via a metastatic process. The bilateral tumors as a group showed more aberrations than did the unilateral ones, consistent with the view that bilaterality is a sign of more advanced disease.

Conclusion

Because some of the imbalances found in borderline ovarian tumors seem to be similar to imbalances already known from the more extensively studied overt ovarian carcinomas, we speculate that the subset of borderline tumors with detectable imbalances or karyotypic aberrations may contain a smaller subset of tumors with a tendency to develop a more malignant phenotype. The group of borderline tumors with no imbalances would, in this line of thinking, have less or no propensity for clonal evolution and development to full-blown carcinomas.

Tumor spreading to the contralateral ovary in bilateral ovarian carcinoma is a late event in clonal evolution

Cancer of the ovary is bilateral in 25%. Cytogenetic analysis could determine whether the disease in bilateral cases is metastatic or two separately occurring primary tumors, but karyotypic information comparing the two cancerous ovaries is limited to a single report with 11 informative cases. We present a series of 32 bilateral ovarian carcinoma cases, analyzed by karyotyping and high-resolution CGH. Our karyotypic findings showed that spreading to the contralateral ovary had occurred in bilateral ovarian cancer cases and that it was a late event in the clonal evolution of the tumors. This was confirmed by the large number of similar changes detected by HR-CGH in the different lesions from the same patient. The chromosomal bands most frequently involved in structural rearrangements were 19p13 (n = 12) and 19q13 (n = 11). The chromosomal bands most frequently gained by both tumorous ovaries were 5p14 (70%), 8q23-24 (65%), 1q23-24 (57%), and 12p12 (48%), whereas the most frequently lost bands were 17p11 (78%), 17p13 (74%), 17p12 (70%), 22q13 (61%), 8p21 and 19q13 (52%), and 8p22-23 (48%). This is the first time that 5p14 is seen gained at such a high frequency in cancer of the ovary; possibly oncogene(s) involved in bilateral ovarian carcinogenesis or tumor progression may reside in this band.

Transcriptional upregulation of human tissue kallikrein 6 in ovarian cancer: clinical and mechanistic aspects

The human tissue kallikrein family (KLK for protein; KLK for gene) includes 15 members. Twelve kallikreins, including KLK6, are concurrently upregulated in ovarian cancer. However, the mechanism of this phenomenon remains unclear. In this study, we measured KLK6 expression in a large series of ovarian tissue cytosols and examined possible mechanisms of KLK6 up-regulation in ovarian cancer. Using a newly developed enzyme-linked immunosorbent assay (ELISA) with two monoclonal antibodies, we quantified KLK6 expression in ovarian tissue cytosols, and confirmed the upregulation of KLK6 in ovarian cancer and its unfavourable prognostic value. We then examined KLK6 mRNA expression using reverse transcription-polymerase chain reaction and established its good concordance with KLK6 protein expression. This finding suggested that the KLK6 gene is under transcriptional regulation. We then scrutinised a few mechanisms that could explain KLK6 upregulation. The relative abundance of two KLK6 mRNA transcripts was studied; we found the same differential expression pattern in all samples, regardless of KLK6 levels. Genomic mutation screening of all exons and the 5'-flanking region of the KLK6 gene identified two linked single-nucleotide polymorphisms in the 5'-untranslated region, but neither correlated with KLK6 expression. Ovarian cell lines were separately treated with five steroid hormones. None of the treatments produced significant effects on KLK6 expression. We conclude that KLK6 is transcriptionally upregulated in ovarian cancer, but probably not through alternative mRNA transcript expression, genomic mutation, or steroid hormone induction.

Higher frequency of chromosomal aberrations in ovarian endometriosis compared to extragonadal endometriosis: A possible link to endometrioid adenocarcinoma

Endometriosis may progress to invasive endometrioid adenocarcinoma, particularly in the ovary. Up to now, little is known of the molecular mechanisms possibly involved in the malignant transformation of endometriosis. Therefore, in this study, extragonadal endometriosis (n = 10), ovarian endometriosis without malignancy (n = 10), ovarian endometriosis with direct transition into endometrioid adenocarcinoma (n = 8), and normal endometrium (n = 12) were investigated for numerical chromosomal aberrations by fluorescence in situ hybridization using centromere enumeration probes. The proportions of cells with aneusomies were semiquantitatively assessed. Trisomies 1 and 7, and monosomies 9 and 17 were found in endometriosis, ovarian endometrioid adenocarcinoma, and normal endometrium. The proportions of aneusomic cells were significantly higher in ovarian endometrioid carcinoma compared with ovarian endometriosis (P < 0.001), and in ovarian endometriosis compared with extragonadal endometriosis and normal endometrium (P < 0.001). The data provide new evidence of a common lineage of endometriosis and ovarian endometrioid carcinoma. The higher frequency of chromosomal aberrations in endometrioid carcinoma than in endometriosis may reflect an expansion of aberrant cell clones already present in endometriosis during the progression to cancer. The higher frequency of chromosomal aberrations in ovarian endometriosis than in extragonadal endometriosis suggests a role of the ovarian stromal milieu in the induction of genetic changes, which may eventually lead to invasive cancer.

Comparative genome hybridization reveals specific genomic imbalances during the genesis from benign through borderline to malignant ovarian tumors

Ovarian cancer is one of the most common types of malignancy in women throughout the developed world. Despite recent therapeutic advances, long-term survival is poor because ovarian cancer is largely asymptomatic in its early stages. Comparative genomic hybridization (CGH) was applied to a series of 8 benign, 8 borderline, and 17 malignant ovarian to establish genomic imbalances associated with tumor progression. Benign and borderline tumors were characterized by losses at 1p32 approximately p11, 2q14 approximately q34, 4q13 approximately q34, 5q11 approximately q23, and 6q12 approximately q24, as well as gains of 6p and chromosome 12. Similar chromosomal changes were also detected in malignant tumors but included additional chromosomal changes: gains at 1q21 approximately q31, 2p, 3q, 5p, 7, 10p, 12p, 16p, 17, 19q, 20q, and 22q, as well as losses at X, 3p, 8p, 9, 11p, 13, 14, and 18. Some individual cases of benign and borderline tumors revealed no genetic alterations detectable by CGH, suggesting that these tumors may represent a subset of tumors that originate by an alternative mechanism of tumorigenesis. Furthermore, our findings reveal that borderline tumors are more similar to benign tumors than to malignant tumors with respect to their genetic profiles.

Non-random structural chromosomal changes in ovarian cancer: i(5p) a novel recurrent abnormality

Ovarian cancer represents the leading cause of death among patients with gynecological cancer. The genetic changes underlying the initiation and progression of ovarian cancer have not been well defined. However, non-random structural chromosomal changes have been identified with common chromosomal breakpoints. We have studied cytogenetically 15 cases of ovarian adenocarcinomas by a direct culture of cancer cells and a G-banding technique investigating the presence of recurrent structural aberrations with common chromosomal breakpoints. Among very complex structural rearrangements found, we could recognize recurrent structural aberrations involving according to frequency chromosomal regions 3p13-14, 11p15, 19q13, 3q21, 11q23, 11q10, 1p13, 1p36, and 17q24-25. Isochromosomes i(5p), i(17q), i(8q) and i(11q) were also observed. Isochromosome i(5p), rarely reported in ovarian cancer was found in seven cases suggesting that it may be a novel recurrent abnormality. Translocations t(1;11), t(3;19), t(3;17), t(7;11) and t(11;17) were also identified. Conventional cytogenetics continues to be valuable detecting the presence of non-random chromosomal breakpoints and facilitating the identification of genes implicated in tumorigenesis.

Aneuploidy and malignancy: an unsolved equation

Aneuploidy is frequently noted in malignant tumours. There is much controversy about its cause and effect in relation to malignant tumours. Failure of the spindle checkpoint caused by mutation of the responsible genes may be one of the important factors for the development of aneuploidy. Telomere dysfunction may also be a possible source of failure of cytokinesis resulting in aneuploidy. Evidence such as tumour specific aneuploidy, presence of aneuploidy in various preneoplastic conditions, increased frequency of genetic instability in aneuploid cell lines compared with diploid cells, and mutation of mitotic checkpoint genes suggests that aneuploidy possibly plays an active role in carcinogenesis. In this brief review, the various aspects of aneuploidy with special emphasis on its mechanism of development and impact on progression of cancer are discussed.

Current challenges and opportunities for research on borderline ovarian tumors

This article summarizes key issues for future research on borderline ovarian tumors that emerged at a National Cancer Institute-sponsored Borderline Ovarian Tumor Workshop held in August 2003 in Bethesda, MD. Limitations in existing research and opportunities for future advances have been highlighted. The application of new molecular techniques in combination with improved study designs holds promise for elucidating the pathogenesis of these tumors and revealing the source of the extra-ovarian lesions ("implants") with which they are frequently associated. Clarification of the etiology of borderline tumors and the pathogenesis of their associated implants is critical for improving pathological diagnosis, revising the classification system of ovarian neoplasms, and developing optimal, evidence-based clinical management algorithms.

Apoptosis stimulating protein of p53 (ASPP2) expression differs in diffuse large B-cell and follicular center lymphoma: correlation with clinical outcome

ASPP2 interacts with the tumor suppressor protein p53, promotes damage-induced apoptosis, and can specifically stimulate p53 apoptotic function. Thus, ASPP2 may function as a tumor suppressor and/or play a role in the cellular response to cytotoxic injury. To explore the role of ASPP2 in human cancer, we determined ASPP2 expression in two lymphoma subtypes with differing clinical outcomes: diffuse large B-cell lymphoma (DLBCL) and follicular center lymphoma (FCL). A real-time reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to detect ASPP2 mRNA. Sixty-one DLBCL and twenty-three FCL cases were analyzed and normalized ASPP2 levels were expressed relative to an mRNA standard. We found that ASPP2 mean expression strongly correlated with lymphoma subtype: DLBCL = 11.74 and FCL = 4.99 (p = 0.029, unpaired 2-tailed t-test). Importantly, ASPP2 expression was variable in DLBCL but not FCL (DLBCL-range, 0.04-94.6; FCL-range, 1.2-15.0). In these DLBCL cases, serum lactate dehydrogenase (LDH) was an independent predictor of survival with median survival in the high LDH group of 24 months and median survival not achieved in the normal-low LDH group (p = 0.014, Log-Rank Test). Mean ASPP2 levels trended toward an inverse correlation with LDH levels: High LDH, ASPP2 = 6.2; Normal-low LDH, ASPP2 = 18.2 (p = 0.074, unpaired 2-tailed t-test). In the DLBCL cases with ASPP2 levels > 7.8, only 10% (1/10) had a high LDH, in contrast to cases with ASPP2 levels < 7.8 in which 59% (26/44) had a high LDH (p = 0.011, Fisher Exact Test). Thus, low ASPP2 mRNA levels may correlate with poor clinical outcome in lymphoma which is consistent with the hypothesis that ASPP2 may play a role in tumor formation and/or sensitivity to cytotoxic agents. Larger studies as well as analysis of different tumor types are warranted.

Genomic imbalances in ovarian borderline serous and mucinous tumors

We analyzed 25 ovarian borderline tumors (13 serous and 12 mucinous tumors) by comparative genomic hybridization (CGH). Genomic imbalance was detected in 85% of serous tumors and 75% of mucinous tumors. Different patterns of genomic alterations were identified in serous and mucinous tumors. Gain of the X chromosome was common in both serous (30%) and mucinous (42%) tumors. However, gain of chromosome 8 was detected exclusively in 38% of serous and mixed sero-mucinous tumors, but not in any pure mucinous tumors. According to the present and previous studies, gain of chromosome 8 is the most common abnormality in borderline serous tumors. Gain of the same chromosome is also common in high grade and advanced stage serous carcinomas, but uncommon in early stage serous carcinomas. In addition gain of chromosome X is common in borderline serous and mucinous tumors, while loss of chromosome X is predominant in invasive carcinomas. These findings do not support the multi-step progression theory from borderline tumor to high-grade, advanced stage carcinoma, but indicate that the borderline ovarian tumor is a distinct entity. Genes in chromosome 8 may be critical for the development and the differentiation of borderline serous tumors.

Cytogenetics and molecular genetics of ovarian cancer

Genetic alterations identified in human ovarian tumors by conventional banding, fluorescence in situ hybridization, comparative genomic hybridization, chromosome microdissection, loss of heterozygosity, chromosome microcell-mediated chromosome transfer, and microarray gene expression analysis are summarized and correlated. The significance of these findings with respect to pathologic classification and clinical application are discussed.

Telomere dysfunction provokes regional amplification and deletion in cancer genomes

Telomere dysfunction and associated fusion-breakage in the mouse encourages epithelial carcinogenesis and a more humanized genomic profile that includes nonreciprocal translocations (NRTs). Here, array comparative genomic hybridization was used to determine the pathogenic significance of NRTs and to determine whether telomere dysfunction also drives amplifications and deletions of cancer-relevant loci. Compared to tumors arising in mice with intact telomeres, tumors with telomere dysfunction possessed higher levels of genomic instability and showed numerous amplifications and deletions in regions syntenic to human cancer hotspots. These observations suggest that telomere-based crisis provides a mechanism of chromosomal instability, including regional amplifications and deletions, that drives carcinogenesis. This model provides a platform for discovery of genes responsible for the major cancers affecting aged humans.

Cloning a cDNA encoding an alternatively spliced protein of BRCA2-associated factor 35

Inheritance of mutations in the breast cancer susceptibility gene, BRCA2, predisposes humans to breast and ovarian cancers. Inherited mutations in the BRCA2 gene are also known to cause susceptibility to prostate cancer. BRCA2 protein exists in a large multi-protein complex from which a novel structural DNA binding protein BRCA2-associated factor 35 (BRAF35) has been isolated. We have cloned a novel cDNA encoding an alternatively spliced protein of BRAF35, designated as BRAF25. BRAF25 transcript is present in various human cells. We have precisely mapped the BRAF25 cDNA sequence to the genomic chromosome 19 sequence. Analysis of the predicted sequence of BRAF25 identified a protein of 215 amino acids. BRAF25 contains a truncated high mobility group domain, a kinesin-like coiled-coil domain and multiple Src homology 2 (SH2) motifs. Western blot analysis using antibodies specific for BRAF25 revealed the presence of BRAF25 in human prostate cancer cells.

Immunohistological detection of BRAF25 in human prostate tumor and cancer specimens

BRAF25 is an alternatively spliced protein of BRAF35 (see associated paper). We have mapped the BRAF25 gene to chromosome sub-band 19p13.3, a region where loss of chromosomal heterozygosity has been reported in about 50% of ovarian cancers. Because of the high incidence of genetic links of prostate cancer to breast and ovarian cancers, we investigated the BRAF25 expression in the prostate specimens. Immunohistochemical analysis using antibodies specific for BRAF25 revealed a strong immunostaining in sections of the benign prostatic hyperplasia (BPH). The staining was concentrated on the nuclei of cells facing the lumen of prostatic glands, even though the sporadic nuclei of cells in stromas were also stained. However, the expression of BRAF25 was dramatically reduced in intermediate prostate cancer and absent in advanced prostate cancer. Preincubation of the antibody with the immunizing peptide abolished immunostaining in BPH specimens. Therefore, the expression of BRAF25 was gradually lost in prostate cancer.

Detection of numerical chromosomal abnormalities in epithelial ovarian neoplasms by fluorescence in situ hybridization (FISH) and a review of the current literature

Preliminary retrospective chromosomal analysis was performed using fluorescence in situ hybridization (FISH) with alphoid DNA probes for chromosomes 1, 3, 6, 8, 12, 17, and X. Twenty-four epithelial ovarian tumors were examined in this pilot study, including 8 borderline (LMP) serous tumors, 9 serous carcinoma, and 7 mucinous carcinoma. Hybridization signals were counted to demonstrate the frequency of aneusomy, trace chromosomal progression, and identify the predominance of chromosome copy number abnormalities that are specific to a particular histotype. The preliminary results revealed almost an equal number of mean aneusomies in serous (58.13 +/- 13%) and mucinous (64.33 +/- 10%) carcinoma, both of which were slightly higher than borderline serous tumors (50.57 +/- 17%). Hyposomies 3 and X were significantly higher in mucinous than in serous ovarian carcinomas, and lowest in borderline serous tumors (P<0.05 and P<0.01). Signal losses were a more frequent abnormality in all three histologic subtypes. Mucinous carcinomas showed a loss of chromosomes 8 (45.00 +/- 28%) and 3 (43.14 +/- 16%), in addition to a loss of chromosome X (56.29 +/- 12%). Serous carcinomas showed a gain of chromosome 1 (39.44 +/- 32%), followed by losses of chromosomes 6 (37.00 +/- 20%), 17 (36.44 +/- 19%), and 8 (36.89 +/- 19%). In borderline serous tumors, the most frequent findings were losses of chromosomes 6 (38.00 +/- 17%), 12 (36.88 +/- 17%), and 3 (36.13 +/- 21%). However, further research is necessary to substantiate these preliminary results and elucidate their clinical significance. A brief review of the literature pertaining to interphase cytogenetics in ovarian epithelial tumors is discussed also.

Comparison of serous and mucinous ovarian carcinomas: distinct pattern of allelic loss at distal 8p and expression of transcription factor GATA-4

Using comparative genomic hybridization (CGH), we have previously demonstrated frequent loss of 8p, especially its distal part, in ovarian carcinoma. To compare the deletion map of distal 8p in serous and mucinous ovarian carcinomas, we performed allelic analysis with 18 polymorphic microsatellite markers at 8p21-p23. In serous carcinoma, loss of heterozygosity (LOH) was detected in 67% of the samples, and the majority of the carcinomas showed loss of all or most of the informative markers. In contrast, only 21% of mucinous carcinomas showed allelic loss, with only one or two loci showing LOH in each sample. In serous carcinomas, LOH was associated with higher grade tumors. Three distinct minimal common regions of loss could be defined in serous carcinomas (at 8p21.1, 8p22-p23.1, and 8p23.1). Expression of a transcription factor gene, GATA4, located at one of these regions (8p23.1) was studied in serous and mucinous ovarian carcinomas by Northern blotting and immunohistochemical staining of tumor microarray. Expression was found to be lost in most serous carcinomas but retained in the majority of mucinous carcinomas. Our results suggest distinct pathogenetic pathways in serous and mucinous ovarian carcinomas and the presence of more than one tumor suppressor gene at 8p involved in the tumorigenesis of serous carcinoma.

A human BRCA2 complex containing a structural DNA binding component influences cell cycle progression

Germline mutations of the human BRCA2 gene confer susceptibility to breast cancer. Although the function of the BRCA2 protein remains to be determined, murine cells homozygous for BRCA2 inactivation display chromosomal aberrations. We have isolated a 2 MDa BRCA2-containing complex and identified a structural DNA binding component, designated as BRCA2-Associated Factor 35 (BRAF35). BRAF35 contains a nonspecific DNA binding HMG domain and a kinesin-like coiled coil domain. Similar to BRCA2, BRAF35 mRNA expression levels in mouse embryos are highest in proliferating tissues with high mitotic index. Strikingly, nuclear staining revealed a close association of BRAF35/BRCA2 complex with condensed chromatin coincident with histone H3 phosphorylation. Importantly, antibody microinjection experiments suggest a role for BRCA2/BRAF35 complex in modulation of cell cycle progression.

BRCA1 and BRCA2 mutations in ovarian cancer: Covariation with specific cytogenetic features

We analyzed 37 primary invasive carcinomas for BRCA1 and BRCA2 mutations by screening the entire coding regions of both genes. Seven predicted truncating mutations (four in BRCA1 and three in BRCA2) and one novel BRCA1 missense variant (S1542C) were identified (8/37, 22%). Two of the BRCA1 mutations were somatic changes, whereas the remaining three BRCA1 changes and all mutations of BRCA2 were found to be of germline origin. All eight BRCA-positive tumors were serous or seropapillary carcinomas (8/27 serous tumors, 30%), and all but one were poorly differentiated. The correlation between tumor karyotype and BRCA status showed that clonal chromosomal aberrations were present in all BRCA-positive tumors (8/8) compared with 20 of 29 BRCA-negative ones. The most consistently affected region in BRCA-positive tumors was the long arm of chromosome 6; alterations within this arm with a breakpoint in band 6q21 were seen in four of five BRCA1-positive and in two of three BRCA2-positive tumors, but only in four of 20 karyotypically abnormal tumors without BRCA mutations, suggesting that the genetic pathways of tumor progression differ in the two groups. The high frequency of germline BRCA mutations detected in this pilot study (16% of 37 invasive carcinomas) points to the need for more extended analyses of population-based series of patients to determine the true contribution of these predisposing genes to the overall incidence of ovarian cancer in this population.

Development of a syngeneic mouse model for events related to ovarian cancer

Mouse ovarian surface epithelial cells (MOSEC) were obtained from virgin, mature mice by mild trypsinization and were repeatedly passaged in vitro. Early passage cells (<20 passages) exhibited a cobblestone morphology and contact inhibition of growth. After approximately 20 passages in vitro, cobblestone morphology and contact inhibition of growth was lost. Tumor forming potential was determined by s.c. and i.p. injection of early and late passage cells into athymic and syngeneic C57BL6 mice. Subcutaneous tumors formed in approximately 4 months and were present only at the injection site. Intraperitoneal injection of late passage MOSEC into athymic and syngeneic mice resulted in growth of tumor implants throughout the abdominal cavity, and production of hemorrhagic ascitic fluid. Early passage MOSEC did not form tumors in vivo. Histopathologic analysis of tumors revealed a highly malignant neoplasm containing both carcinomatous and sarcomatous components. Late passage MOSEC expressed cytokeratin and did not produce ovarian steroids in response to gonadotropin stimulation in vitro. Ten clonal lines were established from late passage MOSEC. Each clone formed multiple peritoneal tumors and ascitic fluid after i.p. injection into C57BL6 mice. Three cell lines examined cytogenetically were polyploid with near-tetraploid modal chromosome numbers. Common clonal chromosome gains and losses included +5, +15, +19 and -X, -3, -4. One cell line had a clonal translocation between chromosomes 15 and 18 and another had a small marker chromosome; common structural abnormalities were not observed. These data describe the development of a mouse model for the study of events related to ovarian cancer in humans. The ability of the MOSEC to form extensive tumors within the peritoneal cavity, similar to those seen in women with Stage III and IV cancer, and the ability of the MOSEC to produce tumors in mice with intact immune systems, makes this model unique for investigations of molecular and immune interactions in ovarian cancer development.

Trisomy of chromosome 10 in two cases of ovarian carcinoma

Simple numerical chromosome aberrations have been observed in tumorigenesis and may point to indicative initiating or early events in tumorigenesis. We have identified two cases of ovarian carcinomas with trisomy of chromosome 10 using conventional GTG-banding and fluorescence in situ hybridization. This is, to our knowledge, the first report of trisomy 10 as a simple karyotypic abnormality observed in ovarian carcinoma. These results suggest that further studies investigating whether chromosome 10 genes are associated with the pathogenesis of some ovarian tumors are warranted.

Numerical abnormalities of chromosomes 1, 11, 17, and X are associated with stromal invasion in serous and mucinous epithelial ovarian tumours

The clinical behaviour of ovarian tumours of low malignant potential (LMP) is unpredictable and it has been suggested that the majority of these lesions have no invasive potential. This study has analysed 92 epithelial ovarian tumours [11 mucinous cystadenomas, 18 mucinous LMP tumours, 15 mucinous carcinomas (9 FIGO stage I), 16 serous cystadenomas, 15 serous LMP tumours, and 17 serous carcinomas (11 FIGO stage I)] for numerical abnormalities of chromosomes 1, 11, 17, and X by interphase cytogenetics. Overall, numerical aberrations were identified in none of the cystadenomas, 15 per cent of serous LMP tumours, 17 per cent of mucinous LMP tumours, 67 per cent of mucinous carcinomas, and 82 per cent of invasive serous carcinomas. In mucinous LMP tumours, chromosome gains were associated with spindled nuclear morphology. Chromosome abnormalities were significantly more frequent in invasive mucinous (overall p< 0.01; stage I p< 0.05) and serous (overall p< 0.001; stage I p< 0.01) carcinomas than in the corresponding LMP tumours. No significant relationship between either stromal invasion or tumour type and the pattern of chromosome loss or gain was identified, although monosomy X was identified almost exclusively in invasive serous carcinomas. These observations are consistent with the concept that LMP tumours are unlikely to be precursors of ovarian carcinoma, but suggest that chromosome instability is important in the development of the invasive phenotype.

Well-differentiated mucinous carcinoma of the ovary and a coexisting Brenner tumor both exhibit amplification of 12q14-21 by comparative genomic hybridization

Although the coexistence of mucinous ovarian neoplasms and Brenner tumors is well established, the histogenesis and developmental relationship between the two remain unknown. We used comparative genomic hybridization to analyze two such tumors occurring simultaneously, one in each ovary, in a patient. Amplification of 12q14-21 sequences was found in both tumors; in addition, both tumors also had other, different changes, four identified in the Brenner tumor and six in the mucinous carcinoma. The occurrence of the same genetic alteration in both tumors in this woman suggests that the mucinous carcinoma and Brenner tumor may be clonally related, i.e., one arose from the other by means of metastatic spreading of transformed cells from one ovary to the other. An alternative explanation is that some unknown, putative tumorigenic agent induced similar and synchronous pathogenetic changes in the epithelium of both ovaries. The phenotypic differences between the tumors are presumably attributable to the other unique genetic abnormalities identified in both tumor types.

Changes of chromosomes 1, 3, 6, and 11 in metastatic effusions arising from breast and ovarian cancer

This cytogenetic study deals with cell material obtained from 15 pleural fluids from 11 patients with breast cancer and 27 ascitic fluids from 16 patients with ovarian cancer; in addition, 8 pleural, 5 ascitic, and 1 pericardial fluid from patients with tuberculosis, liver cirrhosis, and heart insufficiency, were studied. Using mainly direct methods, as well as short-term cell cultures, the chromosome spreads were GTG-banded. Cancerous biopsies showed a plethora of numerical and structural chromosome anomalies and exhibited broad aneuploidy. Chromosomes participating more often in numerical and structural aberrations were 1, 3, 6, 7, 8, 9, 11, 12, and 17. This study provides further cytogenetic evidence for the involvement of these chromosomes in breast and ovarian malignancy.

Molecular aspects of ovarian cancer. Is gene therapy the solution?

Genetic abnormalities of cancer cells are complex and usually nonspecific. Genetic anomalies specific to ovarian cancer have not been reported. This article focuses on what molecular anomalies are known in ovarian cancer and describes the first trials that have used transfer of genes to reestablish a normal cellular function in this disease. Suicide gene therapy has been the prototype of this new therapeutic approach.

Case report: a mixed tumor of the vagina

We report a case of a mixed tumor arising in the vagina of a 64-year old woman. Microscopically, the tumor was composed of stromal-type spindle cells and nests of mature squamous cells embedded in myxomatous stroma. We examined the tumor immunohistochemically, ultrastructurally, and cytogenetically. Based on the results, we discuss the histogenesis of this rare tumor.

Evaluation of FHIT gene alterations in ovarian cancer

The FHIT gene, recently cloned and mapped on chromosome 3p14.2, has frequently been found to be abnormal in several established cancer cell lines and primary tumours. As alterations of chromosome 3p are common events in ovarian cancers with breakpoint sites at 3p14.2, we decided to investigate the role of FHIT in human ovarian tumorigenesis. Fifty-four primary ovarian carcinomas were studied by reverse transcription of FHIT mRNA followed by polymerase chain reaction (PCR) amplification and sequencing of products. The same tumours and matched normal tissues were also investigated for loss of heterozygosity using three microsatellite markers located inside the gene. We found an abnormal transcript of the FHIT gene in two cases (4%) and allelic losses in eight cases (15%). Twelve (22%) of the 54 tumours investigated belonged to young patients with a family history of breast/ovarian cancer. In none of these cases was the FHITgene found to be altered. Our results indicate that FHITplays a role in a small proportion of ovarian carcinomas.

Biological characterization of human epithelial ovarian carcinoma cells in primary culture: the insulin-like growth factor system

Little is known about the factors regulating epithelial ovarian cancer cell growth. This is due, in large part, to the difficulty in obtaining and culturing human ovarian cells for relevant in vitro studies. We recently developed a method for culturing epithelial carcinoma cells derived from fresh, untreated epithelial ovarian cancer specimens. The cell populations are free of fibroblasts and reflect the primary tumor as determined by chromosomal analysis. In this study we report on the cells' growth in serum-free medium and their secretion of CA-125, a glycoprotein marker for ovarian cancer. Furthermore we characterize the insulin-like growth factor (IGF) system in these primary ovarian carcinoma cell cultures. The cells secrete IGF peptides and IGF-binding proteins, possess specific type I IGF receptors, and respond to exogenous IGFs. The culture system reported here provides the basis for further study and manipulation of the IGF system as well as other regulators of epithelial ovarian cancer. Greater understanding of the cellular and molecular mediators of primary human ovarian cancer cell growth may translate into relevant clinical interventions.

Sclerosing stromal tumor of the ovary: a clinicopathologic, immunohistochemical, ultrastructural, and cytogenetic analysis with special reference to its vasculature

Sclerosing stromal tumor (SST) is a rare ovarian neoplasm occurring predominantly in young women and is histologically characterized by cellular heterogeneity, prominent vasculature, and a pseudolobular appearance composed of cellular and hypocellular areas. In the current study, three cases of SST were ultrastructurally examined and the tumors were found to be composed of several kinds of cells, i.e., luteinized thecalike cells, spindle-shaped fibroblastic cells, and primitive mesenchymal cells. These findings thus supported the ovarian stromal origin of SST. Twelve cases of SST also were analyzed immunohistochemically and demonstrated an expression of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) in the luteinized thecalike cells and its receptor, fms-like tyrosine kinase 1 (flt-1), in capillary to medium-sized blood vessels. Reverse transcription-polymerase chain reaction (RT-PCR) also showed an expression of VPF/VEGF messenger RNA in SSTs. Accordingly, the characteristic vasculature and edema of SSTs were considered to be associated with the expression of VPF/VEGF. In addition, a fluorescence in situ hybridization (FISH) analysis also showed cells with three copy number of chromosome 12 in 13-21% of all examined SST cells, which suggested the presence of chromosome 12 trisomy in SSTs as well as in other ovarian stromal tumors.

Loss of heterozygosity in human ovarian cancer on chromosome 19q

Abnormalities in the function of oncogenes and tumor suppressor genes have been associated with many human malignancies. The recognition of sites of loss of heterozygosity (LOH) has led to the identification of such genes. We previously reported that abnormalities of mRNA expression of ERCC1 and ERCC2 may be characteristic of epithelial ovarian carcinoma and brain tumors. This led to an investigation of chromosome 19q13.2-q13.4 which contains these DNA repair genes. A 7-Mb region was analyzed using six microsatellite repeats. Loss of heterozygosity has been identified in 53% (8/15) of cases at marker D19S246 which lies in a 2-Mb segment between HRC and KLK1. The genetic material both centromeric and telomeric to the region of loss was conserved. This area is telomeric to three DNA repair genes where LIG1 is 1-Mb centromeric and ERCC1 and ERCC2 are 3.5- and 4.0-Mb centromeric, respectively. These findings represent the first report of a biologically significant rate of LOH on chromosome 19q13.2-q13.4 in human ovarian carcinoma.

Identical, unique p53 mutations in a primary ovarian mucinous adenocarcinoma and a synchronous contralateral ovarian mucinous tumor of low malignant potential suggest a common clonal origin

The origin of malignant ovarian epithelial tumors is uncertain and has been the subject of considerably controversy. Some favor the theory of origin in precursor lesions such as benign cystadenomas or tumors of low malignant potential (LMP; borderline tumors), whereas others favor the concept of an independent origin of carcinomas from the ovarian surface epithelium or inclusion cysts. Recently, the demonstration of identical molecular alterations in morphologically benign and malignant areas within the same ovarian tumor have suggested the possibility that the malignant epithelium had undergone differentiation to a benign appearance. Because both areas were present in the same tumor, however, the possibility of progression of the morphologically benign component could not be excluded. We present a case of simultaneous mucinous carcinoma and contralateral tumor of LMP which exhibited identical, unique mutations of the p53 gene, suggesting a clonal origin. Because these were separate and distinct tumors, we believe this case provides strong support for the differentiation hypothesis. We also provide evidence for markedly different levels of p53 expression in areas with identical p53 mutations.

Alteration of p16 and p15 genes in common epithelial ovarian tumors

We have examined the roles of 2 putative tumor-suppressor genes, the p16 and p15 inhibitor-of-cyclin-dependent-kinase genes, in the most commonly occurring epithelial tumors of the human ovary. Expression of p16 mRNA, examined by RT-PCR, was significantly reduced in 15 of the 48 tumors. Aberrant expression of p16 protein, detected by immunohistochemistry, occurred in 22 of 60 tumors, more frequently in low-grade tumors, and had significant correlation with low p16 mRNA expression. Hypermethylation of a site within the 5'-CpG island of the p16 gene was significantly associated with loss of p16 mRNA and protein expression. Homozygous gene deletion, evaluated by differential PCR analysis, was found in 2 tumors for the p16 gene and in 1 tumor for the p15 gene among 70 ovarian tumors examined. PCR-SSCP analysis detected point mutations in p16 in 4 tumors and in p15 in 1 tumor. One was a 38-bp deletion, from codons 48 to 60, in a mucinous tumor of low malignant potential; another was a non-sense mutation in codon 60 in a mucinous adenocarcinoma. The remaining 2 mutations were mis-sense mutations, one in codon 58 and the other in codon 60, in 2 endometrioid adenocarcinomas. We conclude that inactivation of p16, by loss of p16 mRNA and protein expression as a consequence of hypermethylation of the 5'-CpG island, rather than by gene deletion or point mutation, may play an important role in the genesis of human ovarian epithelial tumors.

Analysis of loss of heterozygosity and KRAS2 mutations in ovarian neoplasms: clinicopathological correlations

The molecular events that give rise to ovarian epithelial neoplasms are not well understood. In particular, it is not known whether adenocarcinomas arise from benign or low malignant potential (LMP) precursors. We have examined a large series of benign (25) and LMP (31) ovarian tumors for loss of heterozygosity (LOH) at multiple loci on 17 chromosomes. LOH was observed in benign tumors on chromosomes 6 (14%) and 9 (5%) and on the X chromosome (33%) only. LOH on these chromosomes was also detected in a small number of LMP neoplasms, suggesting that these may derive sometimes from benign precursors. In addition, we examined LOH in 93 adenocarcinomas. Analysis of associations between LOH events showed that LOH on chromosomes 5 and 17 (P = 0.0002) and on chromosomes 17 and 18 (P = 0.00007) were associated significantly with each other, which suggests that these may represent cooperative, progressive events. No novel significant associations were identified between LOH events and stage, grade, or histology, which would indicate the existence of genetic heterogeneity in ovarian neoplasms. KRAS2 mutations were detected more often in LMP neoplasms than in malignant tumors (P = 0.004) and were detected more often in Stage I/II malignant tumors than in Stage III/IV malignant tumors (P = 0.033), suggesting that LMP tumors with KRAS2 mutations are unlikely to progress to frank malignancy. Univariate (but not multivariate) survival analysis showed that LOH of chromosomes 11 (P = 0.039) and 17 (P = 0.04) was associated with a significantly worse prognosis. Replication of these novel findings is necessary, and the identification, isolation, and characterization of the critical genes affected by LOH will determine their importance in the pathogenesis of ovarian malignancies.

Loss of heterozygosity at the 5,10-methylenetetrahydrofolate reductase locus in human ovarian carcinomas

The high-affinity folate-binding protein (FBP) is primarily involved in the uptake of the 5-methyltetrahydrofolate, and its expression may be physiologically regulated by the intracellular folate content. The overexpression of FBP on the cell surface of ovarian carcinoma cells may be responsible for an increased folate uptake. We tested the hypothesis of the existence of a defect in the 5, 10-methylenetetrahydrofolate reductase (MTHFR) in ovarian tumours that could cause reduced intracellular regeneration of the 5-methyltetrahydrofolate and induce increased FBP expression. No sequence mutations were found in the MTHFR gene, but allelic deletions of this gene were frequently detected in ovarian tumours (59%). Chromosomal losses appeared to be confined to the 1p36.3 region to which the MTHFR gene maps. Although it cannot be stated that MTHFR is the target gene of the chromosomal loss involving the 1p36.3 region, a correlation between loss of heterozygosity at this locus and decrease in MTHFR activity was shown, suggesting a role of these allelic deletions in generating a biochemical defect in folate metabolism. Further studies are needed to assess further the relationship between MTHFR and FBP overexpression, but the demonstration of the alteration of a key metabolic enzyme of the folate cycle in a subset of human ovarian tumours is in accordance with the hypothesis of an altered folate metabolism in these neoplasias and might be exploited for therapeutic purposes.

Comparative cytogenetic studies of benign, borderline, and malignant epithelial ovarian tumors

Comparative cytogenetic studies were performed in 40 cases of untreated epithelial ovarian tumors. Of these 40 tumors, 13 were classified as benign, 3 as borderline, and 24 as malignant, according to the WHO classification for ovarian tumors. Of 13 benign ovarian tumors, 4 (30.8%) showed chromosomal abnormalities. Of 4 ovarian tumors, 3 (75%) had single chromosomal abnormalities, and the remaining tumor (25%) retained multiple chromosomal abnormalities. Of 3 borderline-malignant ovarian tumors, 2 (66.7%) showed chromosomal abnormalities. Of 2 ovarian tumors, 1 (50%) indicated single chromosomal abnormalities, and the remaining tumor (50%) revealed multiple chromosomal abnormalities. Of 24 malignant ovarian tumors, 20 (83.3%) showed chromosomal abnormalities. Of these 20 ovarian tumors, 3 (15%) had single chromosomal abnormalities, and the other 17 (85%) exhibited multiple chromosomal abnormalities. These data indicate that the rate of chromosomal abnormalities, especially multiple abnormalities, increases following the progression of malignancy in epithelial ovarian tumors.

Karyotypic characteristics of borderline malignant tumors of the ovary: trisomy 12, trisomy 7, and r(1) as nonrandom features

Clonal karyotypic abnormalities were detected in five of 14 cytogenetically analyzed borderline malignant ovarian tumors of clinical stages I-II. One mucinous and one seropapillary tumor had trisomy 7 and r(1)(p36q42) as the sole chromosome abnormality, respectively. Trisomy 12 was found in the remaining three cases. It was the only change in one mucinous and one serous tumor, whereas the third, a seropapillary borderline tumor, had the karyotype 49,XX,+5,+8, +12. These findings, especially when collated with those of previous reports on ovarian borderline tumor cytogenetics, indicate that +12 is the most consistent chromosomal aberration in this group of neoplasms and that also +7 and r(1) are nonrandom features. From the karyotypic point of view, benign ovarian tumors and well-differentiated carcinomas are similar to borderline ovarian tumors, with the possible exception that the former have no tendency to form r(1). Highly malignant carcinomas, on the other hand, are typically much more complex. Chromosome-level changes therefore cannot account for the putative phenotypic passage through the most innocuous tumor stages as epithelial ovarian neoplasms go from benign to fully malignant.

Detection of numerical chromosome anomalies in interphase cells of ovarian carcinomas using fluorescence in situ hybridization

Fluorescence in situ hybridization was used in interphase cells of 30 ovarian carcinomas to detect numerical changes in copy number of 13 different centromeres (1, 2, 3, 4, 6, 7, 8, 10, 11, 12, 17, 18, and X). Thirty-seven percent of samples (11/30) were near diploid and demonstrated only minor changes in centromere copy number, involving gain and/or loss of one or a few centromeres. The most common changes included loss of centromeres 4,6, 17, and 18 and gain of centromere 1. The remaining 63% of samples were hyperdiploid and demonstrated a general increase in copy number of most or all centromeres examined. Among these samples, the centromere of chromosome I was most often found to be at higher copy number. Centromeres that were less often at increased copy or deleted within the hyperdiploid samples include centromeres 4, 17, 18, and X. These results suggest that tumor-suppressor genes that are located on chromosomes 4, 6, 17, and 18 may be involved in the development and progression of ovarian cancer.

Chromosome abnormalities in primary endometrioid ovarian carcinoma

Specific and recurrent chromosome abnormalities may occur in regions of the genome that are involved in the conversion of normal cells to those with tumorigenic potential. Ovarian cancer is the primary cause of death among patients with gynecologic malignancies. We performed cytogenetic analysis in a subgroup of epithelial ovarian tumors, the endometrioid tumors, which are histologically indistinguishable from endometrial carcinoma of the uterus. We studied 10 endometrioid tumors to determine the degree of cytogenetic similarity between these two carcinomas. Six of 10 endometrioid tumors showed a near-triploid modal number, and one had a tetraploid modal number. Eight of the 10 contained structural chromosome abnormalities, of which the most frequent were 1p-- (5 tumors), 6q-- (4 tumors), 19q+ (4 tumors), and chromosome 3 rearrangements (4 tumors). These cytogenetic results resemble those reported for papillary ovarian tumors and differ from those of endometrial carcinoma of the uterus. We conclude that despite the histologic similarities between the endometrioid and endometrial carcinomas, the genetic abnormalities in the genesis of these tumors differ significantly.