The genetic analysis of ovarian cancer

Complexity of the Genetic Background of Oncogenesis in Ovarian Cancer-Genetic Instability and Clinical Implications

Ovarian cancer is a leading cause of death among women with gynecological cancers, and is often diagnosed at advanced stages, leading to poor outcomes. This review explores genetic aspects of high-grade serous, endometrioid, and clear-cell ovarian carcinomas, emphasizing personalized treatment approaches. Specific mutations such as TP53 in high-grade serous and BRAF/KRAS in low-grade serous carcinomas highlight the need for tailored therapies. Varying mutation prevalence across subtypes, including BRCA1/2, PTEN, PIK3CA, CTNNB1, and c-myc amplification, offers potential therapeutic targets. This review underscores TP53's pivotal role and advocates p53 immunohistochemical staining for mutational analysis. BRCA1/2 mutations' significance as genetic risk factors and their relevance in PARP inhibitor therapy are discussed, emphasizing the importance of genetic testing. This review also addresses the paradoxical better prognosis linked to KRAS and BRAF mutations in ovarian cancer. ARID1A, PIK3CA, and PTEN alterations in platinum resistance contribute to the genetic landscape. Therapeutic strategies, like restoring WT p53 function and exploring PI3K/AKT/mTOR inhibitors, are considered. The evolving understanding of genetic factors in ovarian carcinomas supports tailored therapeutic approaches based on individual tumor genetic profiles. Ongoing research shows promise for advancing personalized treatments and refining genetic testing in neoplastic diseases, including ovarian cancer. Clinical genetic screening tests can identify women at increased risk, guiding predictive cancer risk-reducing surgery.

The Unique Biology behind the Early Onset of Breast Cancer

Breast cancer commonly affects women of older age; however, in developing countries, up to 20% of breast cancer cases present in young women (younger than 40 years as defined by oncology literature). Breast cancer in young women is often defined to be aggressive in nature, usually of high histological grade at the time of diagnosis and negative for endocrine receptors with poor overall survival rate. Several researchers have attributed this aggressive nature to a hidden unique biology. However, findings in this aspect remain controversial. Thus, in this article, we aimed to review published work addressing somatic mutations, chromosome copy number variants, single nucleotide polymorphisms, differential gene expression, microRNAs and gene methylation profile of early-onset breast cancer, as well as its altered pathways resulting from those aberrations. Distinct biology behind early-onset of breast cancer was clear among estrogen receptor-positive and sporadic cases. However, further research is needed to determine and validate specific novel markers, which may help in customizing therapy for this group of patients.

KRAS mutation coupled with p53 loss is sufficient to induce ovarian carcinosarcomas in mice

Ovarian carcinosarcoma cancer is the most lethal form of gynecological malignancy, but the pathogenesis and biological function for this ovarian cancer remain unknown. We establishment the transgenic mouse model of K-ras^G12D p53^loxP/loxP and found that K-ras mutation and p53 deletion within the ovarian surface epithelium gave rise to ovarian lesions with a hyperproliferation and endometrioid glandular morphology. Furthermore, double mutant ovaries formed ovarian carcinosarcomas that were high grade and poorly differentiated. Induction was widely metastatic and spread to abdominal organs including liver, spleen, and kidney at 4 wk. We also confirmed the role of K-ras^G12D in ovarian cancer cell lines MCAS and PA-1 and showed that K-ras^G12D overexpression strongly induced cell proliferation, migration, and invasion. The ovarian cancer model we developed recapitulates the specific tumor histomorphology and the probable mechanism of malignant transformation in endometriosis.

Exploiting MEK inhibitor-mediated activation of ERα for therapeutic intervention in ER-positive ovarian carcinoma

While the clinical benefit of MEK inhibitor (MEKi)-based therapy is well established in Raf mutant malignancies, its utility as a suppressor of hyperactive MAPK signaling in the absence of mutated Raf or Ras, is an area of ongoing research. MAPK activation is associated with loss of ERα expression and hormonal resistance in numerous malignancies. Herein, we demonstrate that MEKi induces a feedback response that results in ERα overexpression, phosphorylation and transcriptional activation of ER-regulated genes. Mechanistically, MEKi-mediated ERα overexpression is largely independent of erbB2 and AKT feedback activation, but is ERK-dependent. We subsequently exploit this phenomenon therapeutically by combining the ER-antagonist, fulvestrant with MEKi. This results in synergistic suppression of tumor growth, in vitro and potentiation of single agent activity in vivo in nude mice bearing xenografts. Thus, we demonstrate that exploiting adaptive feedback after MEKi can be used to sensitize ERα-positive tumors to hormonal therapy, and propose that this strategy may have broader clinical utility in ERα-positive ovarian carcinoma.

The role of p53 as a surrogate marker for chemotherapeutical responsiveness in ovarian cancer

INTRODUCTION

In advanced ovarian cancers (OCs), p53 mutations are frequently observed. The objective of this study was to explore the value of the p53 mutational status, using four different techniques, in advanced OC patients as a predictive marker for responsiveness to platinum-based chemotherapy.

METHODS

One hundred and four, mostly serous papillary OC specimens were analyzed, of which all received a platinum containing chemotherapy after optimal cyto-reductive surgery. To verify the p53 mutational status, immunohistochemical staining with monoclonal antibodies, functional yeast assay (FASAY), single-strand conformation polymorphism analysis (SSCP) and genomic sequencing was performed in parallel.

RESULTS

Out of ten OC patients [2 low malignant potential (LMP)/8 G1] only two had a mutant p53, whereas eight showed a wild-type p53. 40 out of 63 (G2/3) patients with G2/3 OC showed mutant p53 and 23 patients showed a wild-type pattern. p53 status was significantly different between these two groups (LMP/G1 vs. G2/3) (P = 0.015). A progressive disease after chemotherapy completion was noted in 35.6% of the patients (26 out of 73); in 69.2%, a mutated p53 and in 30.8%, a wild-type p53 was found. Nine (12.3%) patients showed a complete response at the end of the first-line chemotherapy. Out of these nine patients five had a mutated and four a wild-type p53. A partial response was observed in nine (12.3%) patients of whom four had a mutated p53. With respect to response to first-line chemotherapy (six cycles of platinum containing regimen), the p53 status was not predictive; no statistical significance regarding the p53 mutational status was observed when the two extreme groups PD versus PR/CR were compared (P > 0.05).

CONCLUSION

In this study, the p53 mutational status was not predictive for responsiveness to platinum-based chemotherapy; but p53 was significantly more frequently mutated in poorly differentiated OCs.

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.

Chemotherapy drug response in ovarian cancer cells strictly depends on a cathepsin D-Bax activation loop

The ovarian cancer cell lines A2780 (wild-type p53) and NIHOVCAR3 (mutated p53) showed, respectively, sensitivity and resistance towards several chemotherapy drugs. We hypothesized that the two cell lines differ in their ability to activate the intrinsic death pathway and have, therefore, dissected the lysosome-mitochondrion signalling pathway by pharmacological inhibition or genetic manipulation of key regulators and executioners. Biochemical and morphological confocal fluorescence studies showed that: (1) In A2780 cells bcl-2 is expressed at an undetectable level, whereas Bax is expressed at a rather high level; by contrast, bcl-2 is highly expressed and Bax is expressed at extremely low levels in NIHOVCAR3 cells; (2) Chemotherapy treatment reduced the expression of bcl-2 in NIHOVCAR3 cells, yet these cells resisted to drug toxicity; (3) Cathepsin D (CD), not cathepsin B or L, mediates the activation of the mitochondrial intrinsic death pathway in A2780 cells; (4) Lysosome leakage and cytosolic relocation of CD occurs in the chemosensitive A2780 cells, not in the chemoresistant NIHOVCAR3 cells; (5) Bax is essential for the permeabilization of both lysosomes and mitochondria in A2780 cells exposed to chemotherapy drugs; (6) CD activity is mandatory for the oligomerization of Bax on both mitochondrial and lysosomal membranes; (7) Bax activation did not occur in the resistant NIHOVCAR3 cells despite their high content in CD. The present data are consistent with a model in which on treatment with a cytotoxic drug the activation of a CD-Bax loop leads to the generalized permeabilization of lysosomes and eventually of mitochondria, thus reaching the point of no return, and culminates with the activation of the caspase cascade. Our data also imply that dysfunctional permeabilization of lysosomes contributes to the development of chemoresistance.

Pathogenesis of ovarian cancer: lessons from morphology and molecular biology and their clinical implications

The accepted view of ovarian carcinogenesis is that carcinoma begins in the ovary, undergoes progressive "dedifferentiation" from a well to a poorly differentiated tumor, and then spreads to the pelvic and abdominal cavities before metastasizing to distant sites. It has therefore been reasoned that survival for this highly lethal disease could be improved by developing screening methods that detect disease when it is confined to the ovary. To date, however, no prospective randomized trial of any ovarian cancer screening test(s) has demonstrated a decrease in mortality. We believe that one of the main reasons for this is that the dogma underlying ovarian carcinogenesis is flawed. Based on studies performed in our laboratory during the last decade, we have proposed a model of ovarian carcinogenesis that takes into account the diverse nature of ovarian cancer and correlates the clinical, pathological, and molecular features of the disease. In this model, ovarian tumors are divided into 2 groups designated type I and type II. Type I tumors are slow growing, generally confined to the ovary at diagnosis, and develop from well-established precursor lesions that are termed "borderline" tumors. Type I tumors include low-grade micropapillary serous carcinoma, mucinous, endometrioid, and clear cell carcinomas. They are genetically stable and are characterized by mutations in a number of different genes including KRAS, BRAF, PTEN, and beta-catenin. Type II tumors are rapidly growing highly aggressive neoplasms for which well-defined precursor lesions have not been described. Type II tumors include high-grade serous carcinoma, malignant mixed mesodermal tumors (carcinosarcomas), and undifferentiated carcinomas. This group of tumors has a high level of genetic instability and is characterized by mutation of TP53. The model helps to explain why current screening techniques, aimed at detecting stage I disease, have not been effective. Tumors that remain confined to the ovary for a long period belong to the type I group, but they account for only 25% of the malignant tumors. Most of what is considered ovarian cancer belongs to the type II category, and these are only rarely confined to the ovary. Although the reasons for this are not entirely clear, possible explanations include rapid spread from the ovary early in carcinogenesis and development of carcinoma in extra ovarian sites, notably, the peritoneum and fallopian tube, with secondary involvement of the ovary. The latter tumors are advanced stage at their inception. Therefore, a more realistic end point for the early detection of ovarian cancer is volume and not stage of disease. The model does not replace the histopathologic classification but, by drawing attention to the molecular genetic events that play a role in tumor progression, sheds light on new approaches to early detection and treatment.

Early detection and treatment of ovarian cancer: shifting from early stage to minimal volume of disease based on a new model of carcinogenesis

The goal of ovarian cancer screening is to detect disease when confined to the ovary (stage I) and thereby prolong survival. We believe this is an elusive goal because most ovarian cancer, at its earliest recognizable stage, is probably not confined to the ovary. We propose a new model of ovarian carcinogenesis based on clinical, pathological, and molecular genetic studies that may enable more targeted screening and therapeutic intervention to be developed. The model divides ovarian cancer into 2 groups designated type I and type II. Type I tumors are slow growing, generally confined to the ovary at diagnosis and develop from well-established precursor lesions so-called borderline tumors. Type I tumors include low-grade micropapillary serous carcinoma, mucinous, endometrioid, and clear cell carcinomas. They are genetically stable and are characterized by mutations in a number of different genes including KRAS, BRAF, PTEN, and beta-catenin. Type II tumors are rapidly growing, highly aggressive neoplasms that lack well-defined precursor lesions; most are advanced stage at, or soon after, their inception. These include high-grade serous carcinoma, malignant mixed mesodermal tumors (carcinosarcomas), and undifferentiated carcinomas. The type II tumors are characterized by mutation of TP53 and a high level of genetic instability. Screening tests that focus on stage I disease may detect low-grade type I neoplasms but miss the more aggressive type II tumors, which account for most ovarian cancers. A more rational approach to early detection of ovarian cancer should focus on low volume rather than low stage of disease.

Alteration of cell-cycle regulation in epithelial ovarian cancer

In spite of the clinical importance of epithelial ovarian cancer (EOC), little is known about the pathobiology of its precursor lesions and progression. Regulatory mechanisms of the cell cycle are mainly composed of cyclins, cyclin-dependent kinases (CDK), and CDK inhibitors. Alteration of these mechanisms results in uncontrolled cell proliferation, which is a distinctive feature of human cancers. This review describes the current state of knowledge about the alterations of cell-cycle regulations in the context of p16-cyclin D1-CDK4/6-pRb pathway, p21-p27-cyclin E-CDK2 pathway, p14-MDM2-p53 pathway, and ATM-Chk2-CDC25 pathway, respectively. Recent evidence suggests that ovarian cancer is a heterogenous group of neoplasms with several different histologic types, each with its own underlying molecular genetic mechanism. Therefore, expression of cell cycle regulatory proteins should be tested separately according to each histologic type. In serous ovarian carcinoma, high expression of p16, p53, and p27 and low expression of p21 and cyclin E were shown. In addition, this review focuses on the prognostic significance of cell cycle-regulating proteins in EOC. However, it is difficult to compare the results from different groups due to diverse methodologies and interpretations. Accordingly, researchers should establish standardized criteria for the interpretation of immunohistochemical results.

Benign epithelial ovarian tumours-cancer precursors or markers for ovarian cancer risk?

The natural history of the development of epithelial ovarian cancer remains obscure and no effective screening test exists. In several human malignancies progression from benign to invasive tumour occurs, but this sequence has not been established for epithelial ovarian cancer. We have reviewed epidemiological, histopathological and molecular studies of benign epithelial ovarian tumours to assess the evidence for and against such a progression in ovarian cancer. These data suggest that a diagnosis of a benign ovarian cyst or tumour is associated with an increased risk of ovarian cancer later in life. Current evidence also suggests that benign serous tumours can progress to low-grade serous cancer and that benign mucinous tumours can progress to mucinous cancer. The more common high-grade serous ovarian cancers are likely to arise de novo.

RPS6KA2, a putative tumour suppressor gene at 6q27 in sporadic epithelial ovarian cancer

We had previously defined by allele loss studies a minimal region at 6q27 (between D6S264 and D6S297) to contain a putative tumour suppressor gene. The p90 ribosomal S6 kinase-3 gene (p90 Rsk-3, RPS6KA2) maps in this interval. It is a serine-threonine kinase that signals downstream of the mitogen-activated protein kinase pathway. It is expressed in normal ovarian epithelium, whereas reduced or absent in tumours or cell lines. We show that RPS6KA2 is monoallelically expressed in the ovary suggesting that loss of a single expressed allele is sufficient to cause complete loss of expression in cancer cells. Further, we have identified two new isoforms of RPS6KA2 with an alternative start codon. Homozygous deletions were identified within the RPS6KA2 gene in two cell lines. Re-expression of RPS6KA2 in ovarian cancer cell lines suppressed colony formation. In UCI101 cells, the expression of RPS6KA2 reduced proliferation, caused G1 arrest, increased apoptosis, reduced levels of phosphorylated extracellular signal-regulated kinase and altered other cell cycle proteins. In contrast, small interfering RNA against RPS6KA2 showed the opposite effect in 41M cells. The above results suggest that RPS6KA2 is a putative tumour suppressor gene to explain allele loss at 6q27.

Reduced expression of chemokine (C-C motif) ligand-2 (CCL2) in ovarian adenocarcinoma

Chemokine (C-C motif) ligand-2 (CCL2) is a chemoattractant and activator of macrophages and is a key determinant of the macrophage infiltrate into tumours. We demonstrate here that CCL2 is expressed in normal human ovarian surface epithelium (HOSE) cells and is silenced in most ovarian cancer cell lines, and silenced or downregulated in the majority of primary ovarian adenocarcinomas. Analysis of the CCL2 locus at 17q11.2–q12 showed loss of heterozygosity (LOH) in 70% of primary tumours, and this was significantly more common in tumours of advanced stage or grade. However, we did not detect any mutations in the CCL2 coding sequence in 94 primary ovarian adenocarcinomas. These data support the hypothesis that CCL2 may play a role in the pathobiology of ovarian cancers, but additional studies will be required to evaluate this possibility.

Tumor formation in p53 mutant ovaries transplanted into wild-type female hosts

P53: gene alterations correlate highly with advanced ovarian carcinoma in women. In mice, p53 deficiency predominantly results in the formation of lymphomas and sarcomas. However, ovarian epithelial tumors have not been documented in p53 homozygous mutant (p53-/-) mice, probably because they die before other tumors can form. To determine whether p53-/- ovaries can develop epithelial tumors, they were transplanted into the ovarian bursae of histocompatible wild-type recipient females. The p53-/- ovarian grafts formed tumors approximately 1 year post-transplantation. The tumor type was angiosarcoma, suggesting that vascular tissues are predisposed to tumor formation in p53-/-ovaries. These findings suggest that p53 deficiency alone is not sufficient for ovarian epithelial tumorigenesis in mice. Thus, other genetic lesions are likely required to develop mouse models of human ovarian cancer.

Ovarian tumorigenesis: a proposed model based on morphological and molecular genetic analysis

The pathogenesis of ovarian carcinoma, the most lethal gynecological malignancy, is unknown because of the lack of a tumor progression model. Based on a review of recent clinicopathological and molecular studies, we propose a model for their development. In this model, surface epithelial tumors are divided into two broad categories designated type I and type II tumors that correspond to two main pathways of tumorigenesis. Type I tumors tend to be low-grade neoplasms that arise in a stepwise manner from borderline tumors whereas type II tumors are high-grade neoplasms for which morphologically recognizable precursor lesions have not been identified, so-called de novo development. As serous tumors are the most common surface epithelial tumors, low-grade serous carcinoma is the prototypic type I tumor and high-grade serous carcinoma is the prototypic type II tumor. In addition to low-grade serous carcinomas, type I tumors are composed of mucinous carcinomas, endometrioid carcinomas, malignant Brenner tumors, and clear cell carcinomas. Type I tumors are associated with distinct molecular changes that are rarely found in type II tumors, such as BRAF and KRAS mutations for serous tumors, KRAS mutations for mucinous tumors, and beta-catenin and PTEN mutations and microsatellite instability for endometrioid tumors. Type II tumors include high-grade serous carcinoma, malignant mixed mesodermal tumors (carcinosarcoma), and undifferentiated carcinoma. There are very limited data on the molecular alterations associated with type II tumors except frequent p53 mutations in high-grade serous carcinomas and malignant mixed mesodermal tumors (carcinosarcomas). This model of carcinogenesis reconciles the relationship of borderline tumors to invasive carcinoma and provides a morphological and molecular framework for studies aimed at elucidating the pathogenesis of ovarian cancer.

Molecular genetic analysis of ovarian serous cystadenomas

Ovarian serous cystadenomas are common ovarian lesions that may be precursors of serous borderline tumors, which can in turn progress to low-grade serous carcinomas. It has been shown that low-grade serous carcinoma and serous borderline tumors are characterized by frequent mutations in BRAF or KRAS genes, but the mutational status of these genes in serous cystadenomas and the clonal nature of serous cystadenomas have not been fully investigated. We isolated cyst-lining epithelium from 30 consecutive serous cystadenomas, and analyzed their BRAF and KRAS mutational status. Wild-type sequences of BRAF and KRAS were detected in all specimens. Using the human androgen receptor gene as a polymorphic marker, we also examined the clonal status of epithelial cells in all of the serous cystadenomas. Four of 29 (14%) informative specimens were monoclonal based on the methylation pattern. These monoclonal cystadenomas were significantly (P<0.01) larger in size (>8 cm) than the nonclonal cystadenomas. These data indicate that serous cystadenomas do not contain mutations in either BRAF or KRAS genes and that most serous cystadenomas are polyclonal. Accordingly, it appears that serous cystadenomas develop as a hyperplastic expansion from epithelial inclusions with a clonal/neoplastic transformation occurring in a subset of them.

Loss of heterozygosity on the X chromosome is an independent prognostic factor in ovarian carcinoma

BACKGROUND

Ovarian carcinoma (OC) is the fifth most frequent female cancer type and the fourth most frequent cause of death from cancer among women in Denmark. At the time they are diagnosed with OC, approximately 70% of patients have advanced disease. It is believed that loss of tumor suppressor gene activity plays an important role in the origin and progression of OC and other malignancies. Loss of heterozygosity (LOH) may be detected in individuals heterozygous for an allele and is associated with loss of function of tumor suppressor genes.

METHODS

The polymorphic marker regions (TP53, CACNLB1, D18S58, DXS538, and DXS454) were amplified by polymerase chain reaction followed by separation using gel electrophoresis before LOH was identified. In total, 160 women with primary epithelial OC were included in the study.

RESULTS

Univariate analyses showed significant differences in survival between patients who had advanced OC with LOH or with retention using the microsatellite markers DXS454 (P = 0.04) and DXS538 (P = 0.01). Multivariate Cox regression analysis that included all patients showed that DXS454 (relative hazard [RH] = 3.5; P = 0.002; 95% confidence interval [95% CI], 1.6-7.8), radicality of primary surgery (RH = 5.5; P < 0.0001; 95% CI, 2.7-11.1), and serum tetranectin level (RH = 0.8; P = 0.009; 95% CI, 0.7-0.9) were independent prognostic factors for survival. Multivariate Cox regression analysis restricted to patients with International Federation of Obstetrics and Gynecology Stage III-IV disease showed that DXS454 (RH = 3.4; P = 0.007; 95% CI, 1.4-8.1), radicality of primary surgery (RH = 5.4; P < 0.0001; 95% CI, 2.2-12.9), and serum tetranectin level (RH = 0.8; P = 0.042; 95% CI, 0.7-1.0) were independent prognostic factors.

CONCLUSIONS

LOH at DXS454 (Xq21-q23) appeared to be correlated with reduced survival in patients with OC.

Distribution of HER-2 overexpression in ovarian carcinoma tissue and its prognostic value in patients with ovarian carcinoma: from the Danish MALOVA Ovarian Cancer Study

BACKGROUND

The HER-2 (Human Epidermal Growth factor receptor-2, also known as c-erb-2/neu) protooncogene encodes a transmembrane receptor protein, M(r) 185,000. Studies have shown that the HER-2 oncogene is overexpressed in approximately 25-30% of ovarian carcinoma (OC) cases, but to the authors' knowledge, to date no consensus regarding overexpression and prognosis has been possible. The objective of the current study was first to analyze the presence of HER-2 overexpression in tissue from Danish OC patients and correlate the distribution of HER-2 overexpression with clinical and biochemical data and second to investigate the value of HER-2 overexpression as a prognostic marker in OC and to compare this value with the prognostic value of other biochemical markers.

METHODS

The study population was comprised of the first 181 patients diagnosed with epithelial OC who were included in the MALOVA study. The staining procedure for HER-2 overexpression was performed using the p185 antibody.

RESULTS

HER-2 overexpression was found in 95 of the 181 investigated cases (52.5%), in which 71 carcinomas (39.2%) were weakly positive (1+) and 24 carcinomas (13.3%) were moderately (2+) to intensely positive (3+). Increased HER-2 expression was found to be correlated with reduced survival. Significant differences in survival between patients with (1+, 2+, and 3+) and those without HER-2 overexpression were found for patients with International Federation of Gynecology and Obstetrics (FIGO) Stage I, Stage III, and Stage III/IV OC (Stage I: P = 0.021; Stage III: P = 0.0078; and Stage III/IV: P = 0.0054). Multivariate survival analyses including all 181 OC patients demonstrated that HER-2 overexpression is a prognostic marker (P = 0.003) together with disease stage, serum tetranectin level, and patient age. For patients with Stage III OC, the only independent prognostic factors detected were HER-2 overexpression (P = 0.009) and serum tetranectin level (P <or= 0.0001).

CONCLUSIONS

The results of the current study show that HER-2 overexpression has prognostic value both in univariate and multivariate survival analyses. Therefore, the clinical relevance of this observation should be established conclusively by therapy that targets HER-2 in a prospective Phase II clinical trial.

Genetic analysis of benign ovarian tumors

Ovarian cancer represents a major cause of cancer death among women and yet remarkably little is known about its etiology. The paradigm established by the colorectal carcinogenesis model would suggest that ovarian cancers are likely to arise through malignant transformation of benign ovarian tumors. However, molecular genetic data that could answer this important question is lacking. In our study, we analyzed 80 benign ovarian tumors for TP53 and K-ras mutations and for LOH on chromosomes 6, 7, 9, 11 and 17 using 56 microsatellite markers. Twenty-five percent (5/20) of non-epithelial tumors and 73% (44/60) of epithelial tumors exhibited LOH on at least 1 chromosome arm. A particularly high frequency of LOH was detected among the epithelial tumors on chromosome arms 6q (17%), 7p (17%), 7q (27%) and 11p (18%), which are also regions of frequent LOH among ovarian carcinomas. No K-ras mutations were detected in any tumor but somatic TP53 mutations were detected in 2/34 (6%) serous and 1/26 (4%) mucinous epithelial tumors. In contrast to most previous studies our data is derived from a relatively large number of microdissected tumors and is likely to represent a more accurate picture of the frequency of alterations in these tumors. We conclude that LOH is common in benign ovarian tumors, suggesting that inactivation of tumor suppressor genes are pivotal in their development. The high frequency of alterations is consistent with their being precursors to malignant disease but does not unequivocally prove this continuum. It does however provide a framework for future analysis of the molecular genetic etiology of ovarian tumorigenesis.

TP53 and ovarian cancer

Ovarian cancer represents the fourth most frequent type of cancer among females and is the leading cause of death from gynecological cancer in the western world. This review describes gene alterations in ovarian cancer. Specific emphasis is placed on genetic alterations and the prevalence of TP53 (p53) gene alterations in the distinct biological ovarian tumors (benign, borderline, and malignant) and histological subtypes (serous, mucinous, endometrioid, clear cell), as well as in BRCA1-associated hereditary ovarian cancer. Although multi-modality treatment regimens, including cytoreductive surgery and cisplatin-containing combination chemotherapy, have usefully prolonged survival, the overall cure rate of the disease has not changed dramatically. Ovarian cancer is difficult to eradicate completely by surgery and many patients have only a partial response to postoperative chemotherapy and/or many will develop chemotherapy resistance. All these important factors contribute to the poor prognosis of ovarian cancer patients. In this review, the putative prognostic or predictive value of TP53 in ovarian cancer is addressed.

Analysis of the candidate 8p21 tumour suppressor, BNIP3L, in breast and ovarian cancer

Loss of heterozygosity (LOH) on the short arm of chromosome 8, at 8p12-p23, is one of the most frequent genetic events in both breast and ovarian cancer, suggesting the location of a shared tumour suppressor gene. Microcell-mediated chromosome transfer of chromosome 8 suppresses tumorigenicity and growth of colorectal and prostate cancer cell lines, further supporting the presence of a tumour suppressor gene on 8p. We have taken a candidate gene approach to try to identify this tumour suppressor gene at 8p12-p23. BNIP3L, which has sequence homology to pro-apoptotic proteins and the ability to suppress colony formation in soft agar, is located at 8p21, within a region of ovarian cancer LOH, breast cancer LOH and prostate cancer metastasis suppression. BNIP3L expression was assessed by both RT-PCR and Northern blot analysis in breast and ovarian cancer cell lines and found to be expressed at similar levels relative to expression in their respective normal epithelial cell lines. Genetic analysis of BNIP3L in 40 primary ovarian and 25 primary breast tumours identified one somatic, intronic mutation in one ovarian tumour, as well as several polymorphisms, including one resulting in an amino-acid substitution. These data suggest that BNIP3L is unlikely to be the target of 8p LOH in ovarian or breast cancer.

Chromosome 8 genetic analysis and phenotypic characterization of 21 ovarian cancer cell lines

The short arm of chromosome 8 undergoes frequent loss of heterozygosity (LOH) in ovarian adenocarcinomas. Fine mapping has identified several distinct critical regions within 8p which undergo rates of LOH of 50% or greater, suggesting that there may be more than one tumor suppressor gene located on this chromosome arm. In an effort to refine the location of these putative tumor suppressor genes by homozygosity-mapping-of-deletion analysis, we have analyzed 21 ovarian cancer cell lines with 19 polymorphic microsatellite markers from 8p. Eleven of the cell lines (55%) were homozygous at every marker, indicating loss of an entire 8p arm. No smaller extended regions of hemizygosity were identified. Refinement of these 8p target regions was therefore not possible, but this analysis did identify the ovarian cancer cell lines that would be most appropriate for microcell-mediated chromosome transfer to complement the hypothesized mutation in the target tumor suppressor gene(s) on 8p. The 11 cell lines that had undergone 8p LOH were therefore characterized for colony formation in soft agar and tumor formation in nude mice. We identified four cell lines (JAM, OVCA4, OVCA5, and OVCA8) that were hemizygous for 8p and that formed colonies in soft agar and tumors in nude mice, making them ideal cell lines for chromosome 8 or candidate gene transfer.

The human homologue of unc-93 maps to chromosome 6q27 - characterisation and analysis in sporadic epithelial ovarian cancer

BACKGROUND

In sporadic ovarian cancer, we have previously reported allele loss at D6S193 (62%) on chromosome 6q27, which suggested the presence of a putative tumour suppressor gene. Based on our data and that from another group, the minimal region of allele loss was between D6S264 and D6S149 (7.4 cM). To identify the putative tumour suppressor gene, we established a physical map initially with YACs and subsequently with PACs/BACs from D6S264 to D6S149. To accelerate the identification of genes, we sequenced the entire contig of approximately 1.1 Mb. Seven genes were identified within the region of allele loss between D6S264 and D6S149.

RESULTS

The human homologue of unc-93 (UNC93A) in C. elegans was identified to be within the interval of allele loss centromeric to D6S149. This gene is 24.5 kb and comprises of 8 exons. There are two transcripts with the shorter one due to splicing out of exon 4. It is expressed in testis, small intestine, spleen, prostate, and ovary. In a panel of 8 ovarian cancer cell lines, UNC93A expression was detected by RT-PCR which identified the two transcripts in 2/8 cell lines. The entire coding sequence was examined for mutations in a panel of ovarian tumours and ovarian cancer cell lines. Mutations were identified in exons 1, 3, 4, 5, 6 and 8. Only 3 mutations were identified specifically in the tumour. These included a c.452G>A (W151X) mutation in exon 3, c.676C>T (R226X) in exon 5 and c.1225G>A(V409I) mutation in exon 8. However, the mutations in exon 3 and 5 were also present in 6% and 2% of the normal population respectively. The UNC93A cDNA was shown to express at the cell membrane and encodes for a protein of 60 kDa.

CONCLUSIONS

These results suggest that no evidence for UNC93A as a tumour suppressor gene in sporadic ovarian cancer has been identified and further research is required to evaluate its normal function and role in the pathogenesis of ovarian cancer.

Molecular evidence for putative tumour suppressor genes on chromosome 13q specific to BRCA1 related ovarian and fallopian tube cancer

BACKGROUND/AIMS

Loss of heterozygosity (LOH) on chromosome 13q has been reported to occur frequently in human ovarian cancer, and indications have been found that chromosome 13 may also play a specific role in the inherited form of ovarian cancer. The aim of this study was to define regions on chromosome 13 that may harbour additional tumour suppressor genes involved in the tumorigenesis of BRCA1 related ovarian and fallopian tube cancer.

MATERIALS/METHODS

DNA extracted from paraffin wax blocks of 36 BRCA1 associated ovarian and fallopian tube carcinomas was analysed by LOH polymerase chain reaction using seven highly polymorphic microsatellite markers spanning chromosome 13q.

RESULTS

High LOH frequencies were found on loci 13q11, 13q14, 13q21, 13q22-31, 13q32, and 13q32-4, suggesting the presence of putative tumour suppressor genes on the long arm of chromosome 13 that may play a role in the pathogenesis of BRCA1 related ovarian and fallopian tube cancer. LOH patterns appeared to be independent of the type of BRCA1 mutation, stage, and grade. Although in some cases there were indications for loss of larger parts of chromosome 13, in most cases losses were fairly randomly distributed over chromosome 13 with retained parts in between lost parts. Microsatellite instability was found in six cases.

CONCLUSION

Several loci on chromosome 13q show high frequencies of LOH in BRCA1 related ovarian and fallopian tube cancer, and may therefore harbour putative tumour suppressor genes involved in the carcinogenesis of this particular type of hereditary cancer.

Cellular glutathione content, in vitro chemoresponse, and the effect of BSO modulation in samples derived from patients with advanced ovarian cancer

OBJECTIVES

The objective was to assess the relationship between glutathione content and drug sensitivity with glutathione modulation in ovarian cancer in a pilot study using 31 samples of freshly obtained ovarian tumor material from 26 patients with advanced disease.

METHODS

Processed tumor samples were screened to determine the glutathione content using an enzyme recycling assay modified for use in a 96-well plate format. Chemosensitivity testing (MTT assay) was used to assess sensitivity to cisplatin and doxorubicin and modulation using buthionine sulfoximine. Multidrug-resistance-associated protein MRP1 (putative drug-glutathione conjugate transporter) expression was also assessed.

RESULTS

There was a significant increase in the tumor cell GSH levels in samples from patients who had received previous chemotherapy (9) versus those from chemotherapy-naïve patients (20), P = 0.005. In vitro chemosensitivity testing with doxorubicin and cisplatin (using LC(50) values, i.e., drug dose causing 50% reduction in cell survival relative to untreated control) failed to show a relationship with glutathione levels. Coincubation of cisplatin and doxorubicin with buthionine sulfoximine resulted in a significant increase in sensitivity to both of these drugs overall (cisplatin, P = 0.05; doxorubicin, P = 0.025), with 20 samples showing sensitization to a drug to which they were previously resistant. MRP1 expression failed to show a correlation with drug sensitivity and glutathione levels.

CONCLUSIONS

Our study supports the use of glutathione modulation using agents such as buthionine sulfoximine in patients with heavily pretreated, drug-resistant ovarian cancer.

Physical and transcript map of the region between D6S264 and D6S149 on chromosome 6q27, the minimal region of allele loss in sporadic epithelial ovarian cancer

We have previously shown a high frequency of allele loss at D6S193 (62%) on chromosomal arm 6q27 in ovarian tumours and mapped the minimal region of allele loss between D6S297 and D6S264 (3 cM). We isolated and mapped a single non-chimaeric YAC (17IA12, 260-280 kb) containing D6S193 and D6S297. A further extended bacterial contig (between D6S264 and D6S149) has been established using PACs and BACs and a transcript map has been established. We have mapped six new markers to the YAC; three of them are ESTs (WI-15078, WI-8751, and TCP10). We have isolated three cDNA clones of EST WI-15078 and one clone contains a complete open reading frame. The sequence shows homology to a new member of the ribonuclease family. The other two clones are splice variants of this new gene. The gene is expressed ubiquitously in normal tissues. It is expressed in 4/8 ovarian cancer cell lines by Northern analysis. The gene encodes for a 40 kDa protein. Direct sequencing of the gene in all the eight ovarian cancer cell lines did not identify any mutations. Clonogenic assays were performed by transfecting the full-length gene in to ovarian cancer cell lines and no suppression of growth was observed.

Reduced expression of BAX is associated with poor prognosis in patients with epithelial ovarian cancer: a multifactorial analysis of TP53, p21, BAX and BCL-2

Traditional clinicopathological features do not predict which patients will develop chemotherapy resistance. The TP53 gene is frequently altered in ovarian cancer but its prognostic implications are controversial. Little is known on the impact of TP53-downstream genes on prognosis. Using molecular and immunohistochemical analyses we examined TP53 and its downstream genes p21, BAX and BCL-2 in ovarian tumour tissues and have evaluated the results in relation to clinico-pathological parameters, clinical outcome and response to platinum-based chemotherapy. Associations of tested factors and patient and tumour characteristics were studied by Spearman rank correlation and Pearsons chi2 test. The Cox proportional hazard model was used for univariate and multivariate analysis. The associations of tested factors with response was tested using logistic regression analysis. TP53 mutation, p21 and BCL-2 expression were not associated with increased rates of progression and death. Expression of TP53 was associated with a shorter overall survival only (relative hazard rate [RHR] 2.01, P = 0.03). Interestingly, when combining TP53 mutation and expression data, this resulted in an increased association with overall survival (P = 0.008). BAX expression was found to be associated with both progression-free (RHR 0.44, P = 0.05) and overall survival (RHR 0.42, P = 0.03). Those patients who simultaneously expressed BAX and BCL-2 had a longer progression-free and overall survival compared to patients whose tumours did not express BCL-2 (P = 0.05 and 0.015 respectively). No relations were observed between tested factors and response to platinum-based chemotherapy. We conclude that BAX expression may represent a prognostic indicator for patients with ovarian cancer and that the combined evaluation of BAX and BCL-2 may provide additional prognostic significance.

Decreased expression of the Id3 gene at 1p36.1 in ovarian adenocarcinomas

The molecular events that drive the initiation and progression of ovarian adenocarcinoma are not well defined. We have investigated changes in gene expression in ovarian cancer cell lines compared to an immortalized human ovarian surface epithelial cell line (HOSE) using a cDNA array. We identified 17 genes that were under-expressed and 10 genes that were over-expressed in the cell lines compared to the HOSE cells. One of the genes under-expressed in the ovarian cancer cell lines, Id3, a transcriptional inactivator, was selected for further investigation. Id3 mRNA was expressed at reduced levels in 6 out of 9 ovarian cancer cell lines compared to the HOSE cells while at the protein level, all 7 ovarian cancer cell lines examined expressed the Id3 protein at greatly reduced levels. Expression of Id3 mRNA was also examined in primary ovarian tumours and was found in only 12/38 (32%) cases. A search was conducted for mutations of Id3 in primary ovarian cancers using single stranded conformation polymorphism (SSCP) analysis. Only one nucleotide substitution, present also in the corresponding constitutional DNA, was found in 94 ovarian tumours. Furthermore no association was found between LOH at 1p36 and lack of expression of Id3. These data suggest that Id3 is not the target of LOH at 1p36.

Loss of heterozygosity at chromosomes 3, 6, 8, 11, 16, and 17 in ovarian cancer: correlation to clinicopathological variables

Tumor specimens from 78 epithelial ovarian cancer patients were examined for loss of heterozygosity (LOH) at 11 microsatellite markers at chromosomes 3p14.2, 6q27, 8p12, 11p15.5, 11q23.1-q24, 16q24.3, and 17p13.1, to evaluate the involvement, possible clustering, and prognostic significance of these lesions in the progression of the disease. The LOH analysis was performed on polymerase chain reaction (PCR)-amplified DNA from sections of paraffin-embedded tumor and normal tissue pairs. In addition to primary tumors, specimens of metastatic tissues were studied from 19 patients. In the combined results from primary and metastatic tumors, LOH frequencies varied between 31% (6q27) and 69% (17p13.1). Only LOH at chromosomal regions 3p14.2 (D3S1300), 11p15.5 (D11S1318), 11q23.3-q24 (D11S1340 and D11S912), 16q24.3 (D16S476 and D16S3028), and 17p13.1 (D17S938) was associated with an adverse disease course. Our results indicate that LOH at 17p13.1 occurs independently from the other chromosomal sites studied, and is an early event in ovarian tumorigenesis. The LOH at 16q24.3, 11q23.3/q24, and 11p15.5 seems to occur later. The LOH at 11p15.5 and 11q23.3 was associated with reduced cancer-specific survival time; therefore, the studied markers could be located close to genes with influence on patient survival. Of the studied chromosomal regions, the most important tumor suppressor genes involved in the evolution of ovarian cancer appear to be located on chromosomes 11, 16, and 17. The genetic heterogeneity observed in primary and metastatic specimens demonstrates that there are multiple pathways involved in the progression of ovarian cancer.

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.

Effect of p53 status on sensitivity to platinum complexes in a human ovarian cancer cell line

Wild-type p53 is frequently mutated in late-stage ovarian cancer and has been proposed as a determinant of cisplatin chemosensitivity. We have therefore established a human ovarian cancer cell line differing only in p53 status and characterized its response after treatment with different platinum complexes. The wild-type p53-expressing cell line A2780 was stably transfected with HPV-16 E6 (E6) or an empty vector (VC) as control. Parental A2780 and VC had similar cisplatin sensitivities, whereas E6 was 3- to 4-fold more sensitive as measured by sulforhodamine B and clonogenic assay. E6 was 2- to 3-fold more sensitive to transplatin and the novel cisplatin analog ZD0473 than VC, whereas the trans-platinum analog JM335 was approximately equitoxic. Platinum uptake was similar for all of the cell lines after cisplatin. The removal of platinum-DNA adducts, as measured by atomic absorption spectroscopy, was reduced in E6 compared with VC after cisplatin but similar after JM335. After 10 microM cisplatin, the G(1) population (0-96 h) was reduced in E6 cells compared with VC, whereas the S phase (8-48 h) and G(2) phase (48-96 h) were increased. Similar proportions of VC and E6 cells died by apoptosis, as detected by annexin V binding, but more E6 cells died by necrosis relative to VC. Our results suggest that the loss of functional p53 can increase cisplatin cytotoxicity in A2780, with loss of G(1)/S checkpoint control and decreased cisplatin-DNA adduct repair, but these effects can be circumvented by the use of JM335, which forms different DNA-platinum adducts.

Frequent loss of heterozygosity at 1p36 in ovarian adenocarcinomas but the gene encoding p73 is unlikely to be the target

Loss of heterozygosity (LOH) involving the distal part of the short arm of chromosome 1 occurs frequently in ovarian adenocarcinomas but the tumour suppressor gene(s) targeted by this event is unknown. We have used five microsatellite markers in a panel of 56 ovarian adenocarcinomas to determine which part of 1p34 - 36 is the focus of this LOH. LOH was considerably more common at 1p36 (43%) than at 1p34 - 35 (18%), and 11 tumours showed LOH at 1p36 but not at 1p34 - 35. These data strongly suggest the presence of a tumour suppressor gene inactivated in ovarian adenocarcinoma at 1p36. The p53 homologue, p73, has recently been isolated and mapped to 1p36 and therefore is a candidate for this tumour suppressor gene. However, RT - PCR and Western analyses revealed strong expression of p73 in ovarian adenocarcinoma cell lines but very low or undetectable levels in normal ovarian surface epithelial cells. Immunohistochemical analysis of primary ovarian tumours showed that only 3/22 (14%) contained p73 expressing cells. There was no association between 1p36 LOH and p73 expression in ovarian tumours, nor between p73 and p53 expression. These findings strongly suggest that p73 is not the target of 1p36 LOH in ovarian adenocarcinomas but indicate the presence of an, as yet unidentified, tumour suppressor gene in this region that plays an important role in ovarian tumorigenesis.

Allelic expression of p73 in human ovarian cancers

BACKGROUND

The p73 gene is structurally related to the tumor suppressor gene p53. The role of p73 in tumor development is still unclear and no data on ovarian cancer are so far available. For this reason we have analyzed, in a panel of ovarian cancers, the allelic distribution and expression of p73.

PATIENTS AND METHODS

Fifty-one samples from ovarian cancers and five human ovarian cancer cell lines growing in culture were analyzed. Allelic origin was analyzed by PCR after digestion with the restriction enzyme Sty I. Heterozygous, informative cases were selected for studies aimed at evaluating allelic expression of p73.

RESULTS

We found an allelic distribution similar to that previously reported. LOH was found in two patients with ovarian cancer. In one case in which normal ovarian tissue was available biallelic expression of p73 was found.

CONCLUSION

In comparisons of ovarian cancers and borderline tumors, no differences in allelic distribution and/or expression were found, suggesting that p73 does not play an important role in the pathogenesis and development of ovarian cancer.

Mutation analysis of BRCA1, TP53, and KRAS2 in ovarian and related pelvic tumors

Cancer may be viewed as a genetic disease resulting from critical mutations that disrupt normal cell growth. To characterize the involvement of the BRCA1 and TP53 tumor suppressor genes and of the KRAS2 protooncogene in gynecologic cancer, mutation analysis of these genes was conducted in pelvic tumors of 85 patients that included 49 epithelial ovarian carcinoma cases. The 85 pelvic tumors contained 5 tumors with BRCA1 mutations, 33 with TP53 mutations, and 1 with a KRAS2 mutation. Each of the BRCA1 and KRAS2 mutations, and 25 of the TP53 mutations, were in ovarian carcinomas. Four of the BRCA1 mutations were germline and 1 was somatic. The 4 patients with germline BRCA1 mutations had an early age of disease onset (33-48 years) relative to the mean age of onset (58 years) of all 49 ovarian carcinoma patients, and 3 of these 4 patients had a family history of ovarian or breast cancer. None of the 4 tumors with germline BRCA1 mutations had a KRAS2 mutation or a TP53 mutation, despite a 51% frequency of TP53 mutations in the 49 ovarian carcinomas. Three of the 4 tumors with germline BRCA1 mutations retained a wild-type BRCA1 allele. The tumor with the somatic BRCA1 mutation contained a TP53 mutation and had no evidence for wild-type BRCA1 and TP53 alleles. These data suggest that both BRCA1 and TP53 were inactivated in 1 of 49 ovarian carcinomas. Moreover, mutational inactivation of both BRCA1 and TP53 did not occur in 4 tumors with a germline BRCA1 mutation. It has been proposed that tumorigenesis in cells with a heterozygous BRCA1 mutation requires inactivation of the wild-type BRCA1 and TP53 alleles, which results in genomic instability and acquisition of mutations in protooncogenes. Clearly, mutational inactivation of TP53 and the wild-type BRCA1 allele in ovarian tumors with a heterozygous, germline BRCA1 mutation is not an absolute requirement for tumor formation. It is possible that these alleles may be inactivated by nonmutational mechanisms or that other tumor formation pathways exist.

LOH of chromosome 6q compared with LOH of 17q and 18q in ovarian cancers: relationship to p53 expression and clinicopathological findings

In 41 ovarian epithelial tumors (7 borderline and 34 invasive), loss of heterozygosity (LOH) of chromosomes 6q, 17q, and 18q was examined using 4 microsatellite markers: ER (6q 25-1), BRCA1 (17q21), DCC (18q21), and D18S58 (18q23). The LOH was compared with clinicopathological findings, including p53 and ER expression. In borderline tumors, LOH and p53 expression were never found, while in invasive carcinomas LOH and p53 were found in 71% and 59% of cases, respectively. In particular, in invasive carcinomas 6q LOH represented a marker distinguishing two groups of tumors; those with 6q LOH were only of serous histotype and at advanced stages (III/IV). No significant difference was found for any of genes in 5-year survival of the patients. No correlation was found between ER expression and ER LOH, as well as between biological aggressiveness and 17q and/or 18q LOH. We conclude that p53 and LOH of the investigated loci distinguish borderline from invasive ovarian carcinomas; moreover, the comparison of these results with clinicopathological parameters suggests that the presence of 6q LOH may be a factor accounting for greater biologic aggressiveness independent of the histologic subtype.

Chromosome 11q22.3-q25 LOH in ovarian cancer: association with a more aggressive disease course and involved subregions

Chromosome 11q deletions are common in various malignancies, including ovarian cancer. However, the clinical significance of these genetic lesions as well as their more precise chromosomal location is largely unknown. Here we have examined epithelial ovarian cancer material from 49 patients for loss of heterozygosity (LOH) using nine microsatellite markers on 11q22.3-q25 and evaluated the effect of observed deletions with regard to different clinicopathological variables. LOH was detected in 61% of the patients. Interestingly, LOH for the D11S1340 marker locus at 11q23. 3 seemed to be associated with significantly reduced survival times (P = 0.005) and serous tumor histology (P = 0.036). LOH for D11S912 at the more distal 11q24-q25 location correlated with a higher tumor stage (P = 0.003), serous tumor histology (P = 0.015), and finding of residual tumor (P = 0.047), but not directly with survival times (P = 0.320). The majority of the analyzed tumors simultaneously displayed deletions at two distinct 11q regions, A and B, which are proximal and distal to D11S1347/NCAM (11q23.2-q23.3), respectively. Only LOH for two markers (D11S1340 and D11S912) of the B region seemed to be directly associated with a more aggressive disease course. Therefore, it appears that deletions of the ataxia telangectasia gene of the A region would not be crucial for determining the outcome of ovarian cancer. Our present results indicate that a survival factor gene in ovarian cancer would be located close to D11S1340 at 11q23.3. This corresponds well to our earlier observation in breast cancer, suggesting the involvement of a shared survival factor gene in both diseases.

Analysis of allelic imbalance on chromosome 17p13 in stage I and stage II epithelial ovarian cancers

OBJECTIVES

To determine whether there is evidence for allelic imbalance (AI) on chromosome 17p13 in early-stage epithelial ovarian tumors.

METHODS

Studies of allelic imbalance were performed on 29 stage I or stage II epithelial ovarian cancers using 5 short tandem repeat polymorphic markers (STRPs) on chromosome 17p13 by polymerase chain reaction (PCR) amplification.

RESULTS

Sixteen of 29 (55%) tumors showed AI at one or more loci, including 7 of 29 (24%) tumors that showed distinct regions of AI. AI at p53 was present in only 9 of 25 (36%) informative tumors. A region of AI, defined by marker D17S654, close to candidate genes OVCA1 and OVCA2, was identified distal to p53 and occurred in 11 of 23 (48%) informative tumors. This region of AI also extended more distal to this locus, and included marker D17S695 where AI occurred in 11 of 26 (42%) informative tumors. Microsatellite instability was observed in 2 of 29 tumors.

CONCLUSIONS

This study supports the presence of at least one tumor suppressor gene on chromosome 17p13 distal to p53 that is involved in the early development of epithelial ovarian cancer. This study also suggests that the molecular analysis of early-stage epithelial ovarian cancers can provide important information on the genetic etiology of ovarian cancers.

Induction of p53-dependent and p53-independent cellular responses by topoisomerase 1 inhibitors

We have previously shown that loss of p53 function in A2780 human ovarian adenocarcinoma cells confers increased clonogenic resistance to several DNA-damaging agents, but not to taxol or camptothecin. We have now extended these studies, comparing wild-type p53-expressing A2780 cells with isogenic derivatives transfected with a dominant negative mutant (143; val to ala) p53. We show that, as well as retaining equivalent clonogenic sensitivity to camptothecin, mutant p53 transfectants of A2780 cells do not acquire significantly increased resistance to the camptothecin analogues topotecan and SN-38, the active metabolite of CPT-11. Compared with vector-alone transfectants they are, however, relatively (2.2-fold) resistant to GI 147211, a further camptothecin analogue undergoing clinical trial. Treatment of A2780 with camptothecin and each analogue produces an increase, maximal at 24-48 h after drug exposure, of cells in the G2/M phase of the cell cycle and a decrease in both G1 and S-phase cells. The G2 arrest is independent of p53 function for camptothecin and the three analogues. All four compounds can induce apoptosis in A2780, which is reduced in mutant p53 transfectants, as measured using the terminal DNA transferase-mediated b-d UTP nick end labelling (TUNEL) assay. Thus, although p53-dependent apoptosis is induced by camptothecin, topotecan and SN-38 in this human ovarian carcinoma cell line, these drugs induce p53-independent death, as measured by clonogenic assay.

Correlation of TP53 mutations and p53 expression in ovarian tumors

To characterize the involvement of the TP53 tumor suppressor gene in ovarian cancer, mutation analysis of exons 2-11 of TP53 and immunodetection of its protein product, p53, were done in 48 ovarian tumors. Normally, p53 is not immunodetectable. Missense TP53 mutations have been reported to result in p53 accumulation and detection, but mutations generating premature stop codons have not. Mutations were identified in 19 of 41 malignant tumors but not in 5 benign tumors and 2 tumors of low malignant potential. Fifteen of the 19 tumors with mutations also stained positively by immunohistochemistry or Western blot or both. They included 11 missense mutations, 1 in-frame duplication (474ins6), and 3 frameshift mutations generating premature stop codons. The three tumors with frameshifts also had a wild-type TP53 allele and displayed normal size but not truncated p53 by Western blot. This indicates that these tumors express wild-type p53. The significance of TP53 mutations in the development of the three tumors is questionable unless there is a mechanism for inactivating wild-type p53. Nine of the 19 mutations found here, including the 3 frameshifts, were previously not reported in ovarian cancer. Thirteen of the 19 mutations were single nucleotide substitutions with 6 transitions and 7 transversions. The ratio of transversions to transitions (1.2) was different from literature reports (0.5) (P < 0.01). Thus, the spectrum of TP53 mutations in our study differed from other ovarian tumor reports. This difference may be due to population-based differences in the molecular epidemiology of TP53 mutations.

Molecular characterisation of a panel of human ovarian carcinoma xenografts

In a panel of 16 human ovarian tumours transplanted in nude mice, the expression of genes involved in cell cycle regulation and in response to drug treatment were characterised. In the 16 tumours analysed we could not detect overexpression of Erb-B2 oncogene while expression of MDR1 mRNA was not detected in 11/15 samples and was low in 4/15 tumours. Only three tumours had mutations in the p53 gene exons 5-8 and one of these mutations did not result in any amino acid alteration. The levels of mRNA for cyclins A, D1 and E were heterogeneous with some tumours expressing high levels and others not expressing them at all. The same was found for the cyclin dependent kinases (CDK) CDK2 and CDK4 and for CDK inhibitors p21/WAF1, p27/KIP1 and p16/CDKN2. Two genes belonging to the nucleotide excision repair, ERCC1 and ERCC3 were detectable in all the samples examined, as were the genes MGMT and MAG, also involved in DNA repair. The data indicate a heterogeneity in the expression of genes considered to be involved in the cellular responses to cytotoxic drug treatment and indicate the possibility of using these tumour models to test specifically molecules with a defined mechanism of action.

Loss of heterozygosity on chromosome 6q27 and p53 mutations in epithelial ovarian cancer

Loss of heterozygosity (LOH) in chromosome region 6q27 and p53 mutations were studied to attempt to clarify the genetic etiology of ovarian cancer, with particular reference to clear cell adenocarcinoma (CCC), which has a poor prognosis. 6q27 LOH in 70 epithelial ovarian cancer patients was examined using four restriction fragment length polymorphism markers located at 6q27; p53 mutations in tumor DNA were detected using polymerase chain reaction single-strand conformation polymorphism and sequencing. 6q27 LOH was confirmed in 26 of 48 informative cases (54.2%). No differences in the incidence of 6q27 LOH were seen by histologic type; 6q27 LOH was observed in 45% (5/11) of CCCs. p53 mutations were detected in 19 of the 48 tumors (39.6%), but in only one (9%) CCC. These results suggest that a putative tumor suppressor gene involved in the onset of epithelial ovarian cancer is located at 6q27. This gene is one of the keys to clarifying the genetic etiology of epithelial ovarian cancer and particularly CCC, given the low incidence of p53 mutations in this tumor type.

No evidence for microsatellite instability from allelotype analysis of benign and low malignant potential ovarian neoplasms

The genetic events that lead to the development of benign and low malignant potential (LMP) tumors from normal ovarian surface epithelium are not well understood. In contrast to invasive ovarian neoplasms, loss of heterozygosity (LOH) is not common in these tumors except on the X chromosome, but one report has suggested that an alternative genetic mechanism, microsatellite instability (MSI), might be an important pathogenic mechanism for LMP ovarian tumors.

OBJECTIVE

To determine the frequency of MSI in LMP tumors and to detect novel regions of LOH in benign and LMP ovarian tumors.

METHODS

Sixty-nine microsatellite markers were analyzed in 23 benign and 31 LMP ovarian tumors.

RESULTS

No evidence of MSI was found in any of the tumors studied, nor were any novel regions of LOH identified.

CONCLUSIONS

This suggests that new approaches may be necessary to understand the genetic basis of benign and LMP ovarian neoplasms since neither LOH nor MSI appears to play a major role.

High prevalence of codon 213Arg-->Stop mutations of the TP53 gene in human ovarian cancer in the southwestern part of The Netherlands

As in many human malignancies, TP53 mutations are the most common genetic alterations in malignant human ovarian tumours. An approach often used in the determination of TP53 status is immunohistochemical staining of the protein. Non-missense mutations, especially those of the null type, causing premature termination codons and resulting in truncated proteins, may often not be detectable by immunohistochemistry. Therefore, current estimates of TP53 alterations in ovarian cancer may be inaccurate. By using polymerase chain reaction-single strand conformation polymorphism analysis and sequencing techniques, we have found a high prevalence of TP53 non-missense mutations in exons 5-8 in ovarian tumour specimens from patients from the southwestern part of The Netherlands. Twenty-nine of 64 tumours showed mutations, of which 10 were non-missense mutations. The majority (9 of 10) of these non-missense mutations, including 7 nonsense mutations and 2 frameshift deletions, were null type mutations and could not be detected by immunohistochemical staining. Five of the 7 nonsense mutations were mutations at codon 213 (Arg-->Stop). The nature of the high prevalence of this nonsense mutation in our series of ovarian carcinomas remains unknown. In addition to the 9 null type mutations, a splice junction mutation was encountered. In conclusion, we have observed a high prevalence (13%) of ovarian tumours with null type mutations in exons 5-8 that did not result in immunostaining. Our data suggest that, especially in ovarian cancer, immunological assessment of TP53 is not an adequate tool to study TP53 alteration. A frequent nonsense mutation at codon 213 in 5 (8%) of 64 tumour specimens represents an important finding.

The genetics of ovarian cancer: molecular biology and clinical application

Ovarian cancer is the fifth most common malignancy among American women and the fourth leading cause of cancer death. The rapid advances in molecular genetic analysis, presymptomatic detection, and treatment of ovarian cancer are staggering. In this review, both the genetic component and the molecular biology of ovarian cancer are discussed, as well as current recommendations for genetic counseling. It is important for the practicing obstetrician and gynecologist to become familiar with these concepts, for it is he or she who will likely serve as a primary resource of information for these patients.

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.