Microsatellite instability and alterations in the hMSH2 gene in human ovarian cancer

A COEUR cohort study of SATB2 expression and its prognostic value in ovarian endometrioid carcinoma

The aim of this study was to describe the expression of special AT-rich sequence-binding protein 2 (SATB2) in ovarian endometrioid carcinoma (EC). SATB2 is a nuclear matrix-associated transcription factor that is associated with abnormal expression in certain cancers but has not been reported for ovarian carcinoma. SATB2 mRNA and protein expression was first assessed in a pilot cohort of 26 samples by Affymetrix microarray and by routine immunohistochemistry on a small tissue microarray. A large multicenter validation cohort representing the well-characterized cases of 235 ovarian EC from the Canadian Ovarian Experimental Unified Resource (COEUR) was then used to validate this result and to assess the prognostic impact of SATB2 expression. SATB2 staining was scored as negative, weak, moderate, and strong intensity, and by percentage of stained cells. No SATB2 expression was observed in clear cell carcinomas but 10% (n = 3) of the ECs in the pilot cohort showed SATB2 expression. In the validation cohort, strong expression was observed in 11% of ECs, while weak or moderate expression levels were detected in 12% of cases. Evaluation of SATB2 expression with clinicopathological parameters revealed an association with patient age and Federation International of Gynecology and Obstetrics grade but not with disease stage or postoperative residual disease. Any expression of SATB2, independent of intensity, was also associated with longer survival and improved progression-free survival with hazard ratio (HR) = 0.14 (95% CI 0.03-0.56) and HR = 0.16 (95% CI 0.02-1.24) respectively. A greater beneficial effect was observed in patients with stage III/IV disease compared to patients with stage I/II disease. Furthermore, direct comparison of SATB2 with other reported prognostic biomarkers such as progesterone receptor, CDX2 and β-catenin within this cohort showed that SATB2 had the strongest association with survival. Given the current lack of accurate prognostic factors for these patients, SATB2 has promising clinical utility and warrants further study.

When Is "Type I" Ovarian Cancer Not "Type I"? Indications of an Out-Dated Dichotomy

The dualistic classification of epithelial ovarian cancer (EOC) into “type I” and “type II” is widely applied in the research setting; it is used as a convenient way of conceptualizing different mechanisms of tumorigenesis. However, this classification conflicts with recent molecular insights of the etiology of EOC. Molecular and cell of origin studies indicate that while type II tumors could be classed together, type I tumors are not homogenous, even within the histological types, and can have poor clinical outcomes. Type II high grade serous carcinoma and type I low grade serous carcinomas best fit the description of the dualistic model, with different precursors, and distinct molecular profiles. However, endometriosis-associated cancers should be considered a separate group, without assuming an indolent course or type I genetic profiles. Furthermore, the very clear differences between mucinous ovarian carcinomas and other type I tumors, including an uncertain origin, and heterogeneous mutational spectrum and clinical behavior, indicate a non-type I classification for this entity. The impression that only type II carcinomas are aggressive, have poor prognosis, and carry TP53 mutations is an unhelpful misinterpretation of the dualistic classification. In this review, we revisit the history of EOC classification, and discuss the misunderstanding of the dualistic model by comparing the clinical and molecular heterogeneity of EOC types. We also emphasize that all EOC research, both basic and clinical, should consider the subtypes as different diseases beyond the type I/type II model, and base novel therapies on the molecular characteristics of each tumor.

Recent concepts of ovarian carcinogenesis: type I and type II

Type I ovarian tumors, where precursor lesions in the ovary have clearly been described, include endometrioid, clear cell, mucinous, low grade serous, and transitional cell carcinomas, while type II tumors, where such lesions have not been described clearly and tumors may develop de novo from the tubal and/or ovarian surface epithelium, comprise high grade serous carcinomas, undifferentiated carcinomas, and carcinosarcomas. The carcinogenesis of endometrioid and clear cell carcinoma (CCC) arising from endometriotic cysts is significantly influenced by the free iron concentration, which is associated with cancer development through the induction of persistent oxidative stress. A subset of mucinous carcinomas develop in association with ovarian teratomas; however, the majority of these tumors do not harbor any teratomatous component. Other theories of their origin include mucinous metaplasia of surface epithelial inclusions, endometriosis, and Brenner tumors. Low grade serous carcinomas are thought to evolve in a stepwise fashion from benign serous cystadenoma to a serous borderline tumor (SBT). With regard to high grade serous carcinoma, the serous tubal intraepithelial carcinomas (STICs) of the junction of the fallopian tube epithelium with the mesothelium of the tubal serosa, termed the “tubal peritoneal junction” (TPJ), undergo malignant transformation due to their location, and metastasize to the nearby ovary and surrounding pelvic peritoneum. Other theories of their origin include the ovarian hilum cells.

Target genes of microsatellite sequences in head and neck squamous cell carcinoma: mononucleotide repeats are not detected

Microsatellite instability (MSI) is detected in a wide variety of tumors. It is thought that mismatch repair gene mutation or inactivation is the major cause of MSI. Microsatellite sequences are predominantly distributed in intergenic or intronic DNA. However, MSI is found in the exonic sequences of some genes, causing their inactivation. In this report, we searched GenBank for candidate genes containing potential MSI sequences in exonic regions. Twenty seven target genes were selected for MSI analysis. Instability was found in 70% of these genes (14/20) with head and neck squamous cell carcinoma (HNSCC). Interestingly, no instability was detected in mononucleotide repeats in genes or in intergenic sequences. We conclude that instability of mononucleotide repeats is a rare event in HNSCC. High MSI phenotype in young HNSCC patients is limited to noncoding regions only. MSI percentage in HNSCC tumor is closely related to the repeat type, repeat location and patient's age.

Frequency of mismatch repair deficiency in ovarian cancer: a systematic review This article is a US Government work and, as such, is in the public domain of the United States of America

Loss of mismatch repair (MMR) capacity may represent an important tumor initiating mechanism in ovarian cancer. We conducted a systematic review to analyze the frequency of microsatellite instability (MSI), immunohistochemical (IHC) staining for MMR proteins, and hypermethylation of the MLH1 promoter region in ovarian cancers. Studies examining MSI, loss of MMR gene expression by IHC staining and MLH1 promoter hypermethylation in ovarian cancer were identified by a systematic literature search of the PubMed electronic database through August 31, 2009. Pertinent data was extracted from eligible studies and estimates for pooled proportions were computed using random effects models. The pooled proportion of MSI detection was 0.10 (95% CI, 0.06-0.14) among 1,234 cases in 22 studies. Dinonucleotide markers had a higher frequency of instability than mononucleotide markers. The pooled proportion of MLH1 or MSH2 staining loss was 0.06 (95% CI, 0.01-0.17) among 474 cases in three studies, with a higher frequency of loss in MLH1. The pooled proportion of MLH1 methylation was 0.10 (95% CI, 0.06-0.15) among 672 cases in seven studies. Data reporting MSI and loss of MMR staining in the same cases was limited. Although MMR deficiency was found in all histologic subtypes, endometrioid cancers had the highest proportion. Approximately 10% of unselected ovarian cancers are related to MMR deficiency. While MMR deficiency is associated with improved survival in other MMR-deficiency related cancer sites, epidemiological and clinical factors related to the MMR-deficient phenotype have not been adequately studied in ovarian cancer to date.

An Ashkenazi founder mutation in the MSH6 gene leading to HNPCC

Mutations in DNA mismatch repair genes underlie lynch syndrome (HNPCC). Lynch syndrome resulting from mutations in MSH6 is considered to be attenuated in comparison to that caused by mutations in MLH1 and MSH2, thus more likely to be under diagnosed. In this study we report of a common mutation in the MSH6 gene in Ashkenazi Jews. Genetic counseling and diagnostic work-up for HNPCC was conducted in families who attended the high risk clinic for inherited cancer. We identified the mutation c.3984_3987dup in the MSH6 gene in 19 members of four unrelated Ashkenazi families. This mutation results in truncation of the transcript and in loss of expression of the MSH6 protein in tumors. Tumor spectrum among carriers included colon, endometrial, gastric, ovarian, urinary, and breast cancer. All but one family qualified for the Bethesda guidelines and none fulfilled the Amsterdam Criteria. Members of one family also co-inherited the c.6174delT mutation in the BRCA2 gene. The c.3984_3987dup in the MSH6 gene is a mutation leading to HNPCC among Ashkenazi Jews. This is most probably a founder mutation. In contrast to the c.1906G>C founder mutation in the MSH2 gene, tumors tend to occur later in life, and none of the families qualified for the Amsterdam criteria. c.3984_3987dup is responsible for 1/6 of the mutations identified among Ashkenazi HNPCC families in our cohort. Both mutations: c.3984_3987dup and c.1906G>C account for 61% of HNPCC Ashkenazi families in this cohort. These findings are of great importance for counseling, diagnosis, management and surveillance for Ashkenazi families with Lynch syndrome.

Application of molecular diagnostics for the detection of Lynch syndrome

Lynch syndrome (LS), or hereditary nonpolyposis colorectal cancer, is the most common hereditary colorectal cancer (CRC) syndrome, accounting for approximately 2-5% of all newly diagnosed cases of CRC. Patients with LS have an increased lifetime risk of colorectal (52.2% in women and 68.7% in men) and endometrial cancer (15-70%), as well as certain extra-colonic cancers. Germline mutations in one of several DNA mismatch repair genes underlie LS. Molecular testing has emerged as an indispensable strategy for the diagnosis of LS. The diagnostic work-up of at-risk individuals includes a careful family history evaluation, microsatellite instability, immunohistochemistry and germline DNA analysis. A positive test result can guide clinicians in formulating the appropriate screening, surveillance and management strategies. However, because of the absence of an overt phenotype, such as a diffuse polyposis, it is not always straightforward to recognize LS clinically.

Molecular pathogenesis of endometrial and ovarian cancer

Pregnancy, breastfeeding, and oral contraceptive pill use interrupt menstrual cycles and reduce endometrial and ovarian cancer risk. This suggests the importance of turnover within Mullerian tissues, where the accumulation of mutations in p53 and PTEN has been correlated with number of cycles. The most common type of endometrial cancer (Type I) is endometrioid and molecular abnormalities include mutations in PTEN, KRAS and β-catenin. The Type I precursor is Endometrial Intraepithelial Neoplasia which displays PTEN defects. Type II endometrial cancer (whose precursors are less clear) includes serous and clear cell tumors and the most common alteration is p53 mutation. For ovarian cancer, histopathologic types parallel endometrial cancer and include serous, mucinous, endometrioid, and clear cell; some molecular features are also shared. The most frequent type of ovarian cancer is high grade serous that often displays p53 mutation and its precursor lesions may originate from normal-appearing fallopian tube epithelium that contains a p53 "signature". Mutations in KRAS, BRAF and PTEN are described in mucinous, endometrioid and low grade serous cancers and these may originate from ovarian cortical inclusion cysts. A consideration of molecular and other pathogenetic features, like epidemiology and histopathology, may provide a better understanding of endometrial and ovarian cancer.

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.

Androgen-related expression of G-proteins in ovarian cancer

BACKGROUND

Epidemiological and in vitro data implicate androgens in the aetiology of ovarian cancer, but the mechanisms by which this is mediated are unclear. In this study, we wished to examine the effects of androgens on gene expression in ovarian cancer.

METHODS

The expression of androgen receptor (AR) in OVCAR3 and OSEC2 cells was confirmed using immunoblotting and response to androgens was measured using flow cytometric assessment of S-phase fraction. The differential gene expression between androgen stimulated and unstimulated OVCAR3 ovarian cancer cells was examined with a cDNA microarray. The upregulation of a subset of these genes was then confirmed with reverse transcriptase PCR in both OVCAR3 and OSEC2, an ovarian epithelial cell line. Finally, the clinical significance of this upregulation was investigated by examining the expression of Rab25 and Rab35, two G-protein-related molecules in an ovarian cancer tissue microarray (TMA).

RESULTS

OVCAR3 and OSEC2 cells were shown to express the AR and showed an increase in S-phase fraction in response to androgen treatment. Treatment of OVCAR3 cells with androgen resulted in a significant upregulation of 121 genes. These findings were confirmed for a subset of seven monomeric G-protein-related genes in both OVCAR3 and OSEC2 cells. After staining for Rab25 and Rab35, the majority of TMA sections examined showed expression for Rab25 (92%) and Rab35 (95%). The expression of Rab25 correlated with histological grade, and expression was higher in endometrioid (median histoscore 10.5) than serous (7.5) or mucinous (5.3) tumours. The expression of Rab25 correlated positively with AR expression supporting its role as an androgen responsive gene in ovarian cancer.

CONCLUSIONS

These results suggest that androgens can effect expression of the oncogenic GTPases in ovarian cancer. We propose that the androgen responsive Rab35 may have clinical importance as a biomarker of AR function.

Ovarian cancer

Ovarian carcinomas are a heterogeneous group of neoplasms and are traditionally subclassified based on type and degree of differentiation. Although current clinical management of ovarian carcinoma largely fails to take this heterogeneity into account, it is becoming evident that each major histological type has characteristic genetic defects that deregulate specific signaling pathways in the tumor cells. Moreover, within the most common histological types, the molecular pathogenesis of low-grade versus high-grade tumors appears to be largely distinct. Mouse models of ovarian carcinoma have been developed that recapitulate many of the morphological features, biological behavior, and gene-expression patterns of selected subtypes of ovarian cancer. Such models will likely prove useful for studying ovarian cancer biology and for preclinical testing of molecularly targeted therapeutics, which may ultimately lead to better clinical outcomes for women with ovarian cancer.

Expression and promoter methylation status of mismatch repair gene hMLH1 and hMSH2 in epithelial ovarian cancer

OBJECTIVE

The purpose of this study is to determine the relationship between methylation and loss of hMLH1 and hMSH2 expression in ovarian cancer.

METHODS

We examined the methylation status of hMLH1 and hMSH2 promoter region by methylation-specific polymerase chain reaction (MSP) in 56 primary ovarian cancer tissues and 20 normal ovarian tissues, the relationship between the methylation status of these two genes and clinicopathological characteristics were analysed. We then treated SKOV3 and 3AO ovarian cancer cell lines with the demethylating agent 5-aza-2'-deoxycytidine (5-aza-dc). The hMLH1 and hMSH2 methylation was further assessed by MSP, and their mRNA expression was compared by reverse transcription polymerase chain reaction (RT-PCR) before and after 5-aza-dc treatment in these two cell lines.

RESULTS

The methylation frequency of hMLH1 and hMSH2 was 30.4% (17 of 56) and 51.7% (29 of 56) in ovarian cancers, respectively, while no methylation was detected in normal ovarian tissues (P=0.015). There is a significant correlation between hMLH1 promoter hypermethylation and histological grade (P=0.028) as well as lymphatic metastasis (P=0.003). Methylation of hMSH2 correlated with histological grade (P=0.035) and lymphatic metastasis (P=0.015). Besides, the methylation rates of hMSH2 were significantly higher in endometrioid adenocarcinoma tissues than in other pathological types of ovarian cancer. After 5-aza-dc treatment, the expression of hMLH1 and hMSH2 was reversed in two cell lines.

CONCLUSION

Our results indicate that promoter hypermethylation is an important mechanism for loss of hMLH1 and hMSH2 expression in human ovarian cancer and may be a potential prognostic factor in ovarian cancer.

Hereditary ovarian carcinoma: heterogeneity, molecular genetics, pathology, and management

Hereditary ovarian cancer accounts for at least 5% of the estimated 22,000 new cases of this disease during 2009. During this same time, over 15,000 will die from malignancy ascribed to ovarian origin. The bulk of these hereditary cases fits the hereditary breast-ovarian cancer syndrome, while virtually all of the remainder will be consonant with the Lynch syndrome, disorders which are autosomal dominantly inherited. Advances in molecular genetics have led to the identification of BRCA1 and BRCA2 gene mutations which predispose to the hereditary breast-ovarian cancer syndrome, and mutations in mismatch repair genes, the most common of which are MSH2 and MLH1, which predispose to Lynch syndrome. These discoveries enable relatively certain diagnosis, limited only by their variable penetrance, so that identification of mutation carriers through a comprehensive cancer family history might be possible. This paper reviews the subject of hereditary ovarian cancer, with particular attention to its molecular genetic basis, its pathology, and its phenotypic/genotypic heterogeneity.

Systematic review and meta-analysis of ovarian cancers: estimation of microsatellite-high frequency and characterization of mismatch repair deficient tumor histology

PURPOSE

A meta-analytic approach was used to estimate the frequency of: (a) microsatellite instability-high (MSI-H) phenotype in unselected ovarian cancers and (b) various histologic subtypes of mismatch repair (MMR)-deficient epithelial ovarian cancers.

METHODS

A systematic search of the Medline electronic database was conducted to identify articles published between January 1, 1966, and December 31, 2007, that examined MMR deficiency in ovarian cancers. Data were extracted on the study population, sample size, MSI-H frequency, and histology of MMR-deficient ovarian tumors.

RESULTS

The pooled proportion of MSI-H ovarian cancers was 0.12 [95% confidence interval (CI), 0.08-0.17] from 18 studies with 977 cases. The proportion of histologic subtypes in the pooled analysis from 15 studies with 159 cases was serous at 0.32 (95% CI, 0.20-0.44), mucinous at 0.19 (95% CI, 0.12-0.27), endometrioid at 0.29 (95% CI, 0.22-0.36), clear cell at 0.18 (95% CI, 0.09-0.28), and mixed at 0.24 (95% CI, 0.07-0.47). There was significant heterogeneity between studies.

CONCLUSIONS

The frequency of the MSI-H phenotype in unselected ovarian cancers approximates 12%. MMR-deficient ovarian cancers also seem to be characterized by an overrepresentation of nonserous histologic subtypes. Knowledge of histologic subtype may aid clinicians in identifying the relatively large proportion of ovarian cancers due to MMR defects; such knowledge has potential implications for medical management.

A review of the clinical relevance of mismatch-repair deficiency in ovarian cancer

Ovarian cancer ranks fifth in both cancer incidence and mortality among women in the United States. Defects in the mismatch-repair (MMR) pathway that arise through genetic and/or epigenetic mechanisms may be important etiologically in a reasonable proportion of ovarian cancers. Genetic mechanisms of MMR dysfunction include germline and somatic mutations in the MMR proteins. Germline mutations cause hereditary nonpolyposis colorectal cancer (HNPCC), which is the third most common cause of inherited ovarian cancer after BRCA1 and BRCA2 mutations. An epigenetic mechanism known to cause inactivation of the MMR system is promoter hypermethylation of 1 of the MMR genes, mutL homolog 1 (MLH1). Various laboratory methods, in addition to clinical and histopathologic criteria, can be used to identify MMR-deficient ovarian cancers. Such methods include microsatellite instability analysis, immunohistochemistry, MLH1 promoter hypermethylation testing, and germline mutation analysis. In this review, the authors describe the existing literature regarding the molecular, clinical, and histologic characteristics of MMR-deficient ovarian cancers along with the possible effect on survival and treatment response. By further defining the profile of MMR-deficient ovarian cancers and their associated etiologic mechanisms, there may be a greater potential to distinguish between those of hereditary and sporadic etiology. The ability to make such distinctions may be of diagnostic, prognostic, and therapeutic utility.

Microsatellite instability and mismatch repair protein defects in ovarian epithelial neoplasms in patients 50 years of age and younger

Ovarian malignancies occurring in the setting of hereditary nonpolyposis colorectal carcinoma syndrome typically present in young women, often as the first or "sentinel" cancer, but the frequency of microsatellite instability (MSI) and mismatch repair (MMR) defects in ovarian surface epithelial malignancies in women <or=50 years of age is neither well known nor well tested. Fifty-two ovarian surface epithelial carcinomas, including 4 with synchronous endometrial carcinomas, were identified in patients 50 years of age or younger and evaluated for evidence of MSI and MMR protein deficiency. Each case was tested for MSI by multiplex polymerase chain reaction amplification of the National Cancer Institute reference panel (BAT25, BAT26, D2S123, D5S346, and D17S250) and deficiency of MMR protein expression by immunohistochemistry (MLH1, MSH2, MSH6, and PMS2). MMR protein expression and MSI (in a subset of cases) were also evaluated in 50 unselected ovarian serous tumors of low malignant potential , a tumor common in younger women. Defects in MMR were detected in 5 of 52 (10%) ovarian carcinomas by at least 1 testing method, including 2 of 4 (50%) ovarian cancers presenting with synchronous endometrial cancer. Three of the 5 (60%) ovarian carcinomas were clear cell carcinomas (17% of all pure clear cell carcinomas) and the remaining 2 were high-grade carcinomas with endometrioid and mixed histology. Loss of MSH2 and MSH6 was detected in all of the affected clear cell carcinomas and a synchronous endometrial cancer with endometrioid histology. Loss of 1 or more MMR proteins was initially noted in 10/50 ovarian serous tumors of low malignant potential on tissue microarray, but further testing on full tissue sections showed intact protein expression and microsatellite stability in all informative cases. This study demonstrates a 10% rate of MMR-deficient ovarian cancer in women <or=50 years of age. MMR-deficient ovarian cancer is frequently associated with loss of expression of MSH2 and MSH6 proteins and clear cell histology. The occurrence of MMR inactivation in a significant proportion of ovarian clear cell carcinomas (17% in this study) suggests that this tumor may warrant targeted testing in women <or=50 years of age.

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.

Clinical significance of microsatellite instability in sporadic epithelial ovarian tumors

PURPOSE

We evaluated the expression of microsatellite instability (MSI) in sporadic ovarian tumors using 5 standard and 9 new MSI markers to determine the clinical significance of MSI in sporadic epithelial ovarian tumors.

MATERIALS AND METHODS

MSI was examined in 21 borderline and 25 malignant ovarian tumors. Polymerase chain reaction (PCR) was performed using the 5 markers recommended by the National Cancer Institute (NCI) for colon cancer and 9 additional markers. MSI was determined using fractional analysis by mixing the PCR products and size markers.

RESULTS

Using the 5 conventional MSI markers, MSI was found in 4 of 46 (8.6%) ovarian tumors, including 2 of 21 (9.5%) borderline ovarian tumors and 2 of 25 (8%) malignant ovarian tumors. Using the 9 additional MSI markers, MSI was observed in 7 of 46 (15.2%) ovarian tumors, including 3 of 21 (14.3%) borderline ovarian tumors and 4 of 25 (16%) malignant ovarian tumors. There was no statistically significant difference between MSI and clinicopathological factors, including histology and stage, although there was a trend toward an increased incidence of MSI in the serous type.

CONCLUSION

MSI was infrequent in ovarian tumors, including both borderline and malignant tumors. MSI was found to be uncommon in sporadic ovarian tumors, even by using additional MSI markers. The clinical significance of MSI is not strong in patients with sporadic ovarian tumors.

Mutation spectrum in HNPCC in the Israeli population

Hereditary non-polyposis colon cancer is caused by mutations in DNA mismatch repair genes. The mutation spectrum in the Israeli population is poorly documented except for the c.1906G>C Ashkenazi founder mutation in the hMSH2 gene. To report our experience in HNPCC screening, the mutations detected and the clinical features among a cohort of Israeli patients. Diagnostic work-up was done in a multi-step process guided by clinical and ethnic information. Tumors of suspected patients were tested for microsatellite instability and immunohistochemistry. Based on tumor analyses, we proceeded to mutation screening by DHPLC followed by sequence analysis and multiplex ligase dependent probe amplification. Ashkenazi Jews were first tested for the c.1906G>C founder mutation. Of the 240 families, 24, including Arabs and Jews from different ethnic origins, were tested positive. All tumors that lost expression of mismatch repair proteins also showed microsatellite instability. There was evidence for involvement of hMSH2 (15) hMLH1 (6) and hMSH6 (3) genes. Mutations were identified in 17/24 (71%) patients: 6 Ashkenazi families harbored the c.1906G>C mutation. Eleven other mutations (2 nonsense, 3 splice site and 6 small deletions) were detected. Three of the mutations are novel. No gross deletions or insertions were detected. This is the first report that characterizes the profile of HNPCC in a cohort of patients in Israel. Tumor testing indicated that the 3 main MMR genes are involved, and that mutation spectrum is broad.

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.

Single-nucleotide polymorphisms of mismatch repair genes in healthy Chinese individuals and sporadic colorectal cancer patients

Mismatch repair (MMR) genes are among of the most important genes associated with colorectal cancer (CRC). Single-nucleotide polymorphisms (SNPs) are generally thought to provide important information across a wide spectrum of life sciences; however, no study of association between SNPs of MMR genes and Chinese sporadic colorectal cancer (SCRC) is available. We chose 29 reported single-nucleotide variants that have rarely been verified in a population-based study. We identified SNPs and the genotype-phenotype association in Chinese populations of 150 healthy individuals and 160 SCRC patients. We extracted the genomic DNA from the blood of these individuals and used sequencing to determine these SNPs. Three SNPs (MLH1 394G-->C, 655A-->G, 1151T-->A) occurred with a frequency of 8.8-11.2% in the Chinese population. These SNPs formed a series with combined effects. The haplotype of concurrent MLH1 655 and 1151 SNPs and the haplotype combinations of MLH1 1151, MLH1 394 occurred exclusively in SCRC. None of the other 26 variants were detected in the Chinese population.

Molecular mechanisms of resistance and toxicity associated with platinating agents

Platinating agents, including cisplatin, carboplatin, and oxaliplatin, have been used clinically for nearly 30years as part of the treatment of many types of cancers, including head and neck, testicular, ovarian, cervical, lung, colorectal and relapsed lymphoma. The cytotoxic lesion of platinating agents is thought to be the platinum intrastrand crosslink that forms on DNA, although treatment activates a number of signal transduction pathways. Treatment with these agents is characterized by resistance, both acquired and intrinsic. This resistance can be caused by a number of cellular adaptations, including reduced uptake, inactivation by glutathione and other anti-oxidants, and increased levels of DNA repair or DNA tolerance. Here we investigate the pathways that treatment with platinating agents activate, the mechanisms of resistance, potential candidate genes involved in the development of resistance, and associated clinical toxicities. Although the purpose of this review is to provide an overview of cisplatin, carboplatin, and oxaliplatin, we have focused primarily on preclinical data that has clinical relevance generated over the past five years.

Immunohistochemical staining of hMLH1 and hMSH2 reflects microsatellite instability status in ovarian carcinoma

Microsatellite instability is due to defects in the family of DNA repair genes, primarily hMLH1 and hMSH2, which can be detected by immunohistochemical staining. However, it is unclear whether immunohistochemical staining can accurately predict microsatellite instability status. We sought here to evaluate the sensitivity, specificity, and predictive values of immunostaining for the expression of the DNA mismatch-repair genes hMLH1 or hMSH2 in predicting microsatellite instability in ovarian carcinoma. Tissue microarrays with specimens from 322 women with primary ovarian carcinoma were stained with antibodies to hMLH1 and hMSH2; cases in which either hMLH1 or hMSH2 were negative were analyzed for microsatellite instability with the five-marker panel recommended by the National Cancer Institute (BAT26, BAT25, D5S346, D2S123, and D17S250). Microsatellite instability was also analyzed in another 19 cases selected at random in which both hMLH1 and hMSH2 were positive. Tumors with instability at two or more of the five NCI markers were considered to have a high level of microsatellite instability; tumors showing instability at only one marker were considered microsatellite instability-low; and tumors in which no markers exhibited microsatellite instability were considered microsatellite stable. We found that negative staining for hMLH1 protein (five cases) or hMSH2 protein (two cases) was associated with high level of microsatellite instability. The sensitivity and specificity of immunohistochemical staining for hMLH1 were 62 and 100% and those of hMSH2 alone were 25 and 100%. Combining loss of expression of both hMLH1 and hMSH2 led to sensitivity, specificity, and positive and negative predictive values of 87, 100, 100, and 95%. These results suggest that use of a two-molecule panel (hMLH1 and hMSH2) can accurately determine the microsatellite instability status of patients with ovarian cancer.

Patterns of loss of heterozygosity at 10q23.3 and microsatellite instability in endometriosis, atypical endometriosis, and ovarian carcinoma arising in association with endometriosis

Genetic aberrations, such as loss of heterozygosity (LOH) and mutations leading to functional inactivation of the PTEN tumor suppressor gene, located on chromosome 10q23.3, have been shown to be associated with approximately one third of ovarian adenocarcinomas. In addition, microsatellite instability (MSI) leading to the functional inactivation of the PTEN gene has also been reported for ovarian adenocarcinomas with frequencies varying from 6 to 37%. However, the frequency of PTEN gene abnormalities has not been well studied or evaluated in lesions such as typical and atypical endometriosis. The aim of this study was to investigate a possible sequential progression from endometriosis through atypical endometriosis to ovarian carcinoma by assessing LOH at 10q23.3 and MSI in those entities. Genomic DNA was analyzed for LOH and MSI at 3 loci on chromosome 10, using polymerase chain reaction amplification. Significant differences in LOH were seen between endometriosis (4.3%) and ovarian carcinoma (23.5%) at D10S608. The differences at the other 2 loci were not significant. A high frequency of MSI was found in endometriosis (82.6%) and atypical endometriosis (75%); however, the differences were not significant. These results suggest that LOH at D105608 may possibly be an important molecular event in the progression of endometriosis to carcinoma. This study highlights that endometriosis and atypical endometriosis might act as precursor lesions that have the potential to progress into ovarian adenocarcinoma.

Mismatch repair and treatment resistance in ovarian cancer

BACKGROUND

The treatment of ovarian cancer is hindered by intrinsic or acquired resistance to platinum-based chemotherapy. The aim of this study is to determine the frequency of mismatch repair (MMR) inactivation in ovarian cancer and its association with resistance to platinum-based chemotherapy.

METHODS

We determined, microsatellite instability (MSI) as a marker for MMR inactivation (analysis of BAT25 and BAT26), MLH1 promoter methylation status (methylation specific PCR on bisulfite treated DNA) and mRNA expression of MLH1, MSH2, MSH3, MSH6 and PMS2 (quantitative RT-PCR) in 75 ovarian carcinomas and eight ovarian cancer cell lines

RESULTS

MSI was detected in three of the eight cell lines i.e. A2780 (no MLH1 mRNA expression due to promoter methylation), SKOV3 (no MLH1 mRNA expression) and 2774 (no altered expression of MMR genes). Overall, there was no association between cisplatin response and MMR status in these eight cell lines. Seven of the 75 ovarian carcinomas showed MLH1 promoter methylation, however, none of these showed MSI. Forty-six of these patients received platinum-based chemotherapy (11 non-responders, 34 responders, one unknown response). The resistance seen in the eleven non-responders was not related to MSI and therefore also not to MMR inactivation.

CONCLUSION

No MMR inactivation was detected in 75 ovarian carcinoma specimens and no association was seen between MMR inactivation and resistance in the ovarian cancer cell lines as well as the ovarian carcinomas. In the discussion, the results were compared to that of twenty similar studies in the literature including in total 1315 ovarian cancer patients. Although no association between response and MMR status was seen in the primary tumor the possible role of MMR inactivation in acquired resistance deserves further investigation.

Prognostic significance of p53 mutation in suboptimally resected advanced ovarian carcinoma treated with the combination chemotherapy of paclitaxel and carboplatin

The prognostic significance of p53 mutation, microsattelite instability and DNA mismatch protein hMLH1 expression in suboptimally resected advanced ovarian carcinoma treated with the combination chemotherapy of paclitaxel and carboplatin was evaluated. The overall combination chemotherapy response rate and the complete remission rate were significantly higher among patients with mutant p53 tumors than those with wild-type p53 tumors (35/42 (83%) vs. 32/58 (55%); P=0.003 and 18/42 (43%) vs. 16/58 (28%); P=0.03, respectively). This tendency apparently existed in non-serous carcinoma, but not in serous carcinoma. Univariate analysis showed that the risk of death due to disease and risk of progression was significantly lower among patients with p53 mutation (P=0.0357 and 0.0281, respectively). However, the presence of microsattelite instability or loss of hMLH1 expression was not associated with either the clinical response or prognosis. Determining p53 mutational status can be useful in predicting therapeutic response to drugs in ovarian carcinoma, especially in non-serous tumors.

The contribution of the hereditary nonpolyposis colorectal cancer syndrome to the development of ovarian cancer

OBJECTIVE

Ovarian cancer has one of the highest fractions of hereditary cases. The hereditary breast and ovarian cancer syndrome, primarily due to mutations in BRCA1 and BRCA2, is the main cause of heredity, but also the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome confers an increased risk of ovarian cancer. In order to clarify the contribution of HNPCC to the development of ovarian cancer, we collected data on family history of cancer and characterized MMR function in a consecutive series of 128 tumors unselected for age at diagnosis and previously characterized for BRCA gene mutations.

METHODS

Expression of the MMR proteins MLH1, PMS2, MSH2, and MSH6 was analyzed by immunohistochemistry using tissue microarray sections. Tumors with reduced staining or loss of staining were also analyzed for microsatellite instability (MSI).

RESULTS

Loss of MMR protein expression was identified in 3 ovarian cancers, all of which had a MSI-high phenotype. DNA sequence analysis revealed disease-causing germline mutations (deletions of exons 4-6 in MLH1 and a 1-nucleotide deletion in exon 5 of MSH6) in two patients diagnosed at ages 40 and 49 years, both of whom had family histories suggestive of HNPCC. The genetic defect in the third case, which was a 47-year old woman without knowledge about her family history with loss of MLH1/PMS2 expression in the tumor tissue, remains elusive. A family history suggestive of HNPCC was identified in an additional case, but this tumor showed normal, retained MMR protein expression and a microsatellite stable phenotype.

CONCLUSIONS

About 2% of ovarian cancer is caused by germline mutations in the MMR-genes, a minor proportion as compared to the contribution of the BRCA-genes (11% in the present series). However, identification of HNPCC patients is important since it allows inclusion of high-risk individuals into control programs aimed at preventing the more frequent colorectal and endometrial cancers. Tumors within the HNPCC-spectrum should therefore be included when recording a family history of cancer among patients diagnosed with ovarian cancer.

Establishment of an immortalised human ovarian surface epithelial cell line without chromosomal instability

Epithelial ovarian carcinoma is thought to derive from ovarian surface epithelium (OSE). The black box of the early molecular changes in ovarian carcinogenesis is being interpreted by the development of experimental systems employing immortalised human OSE cells. However, the existing cell lines of the OSE cells have limited utility due to chromosomal instability. Our goal was to establish new immortalised human OSE cells that retain the original characteristics of the primary cells without chromosomal alterations. Using primary human OSE cells obtained from a postmenopausal patient with endometrial cancer, five cell lines (‘HOSE1’ lines) were newly established by infection with retroviral expression vectors containing type 16 human papillomavirus (HPV-16) E6, E7, a variant E6 (E6Δ151), and Bmi1 polycomb gene, in combination with telomerase reverse transcriptase (hTERT). Consequently, five HOSE1s cell lines, HOSE1s-E6/hTERT, -E7/hTERT, -E6/E7/hTERT, -E6Δ151/E7/hTERT, and -E6Δ151/Bmi1/hTERT, grew beyond the population doubling number of 200. These cell lines, except for HOSE1-E6/hTERT, essentially showed the original features of the primary human OSE cells. Of them, HOSE1-E7/hTERT preserved diploidy in a kariotype analysis, and did not show transformed phenotypes in anchorage-independent growth and tumour formation. Thus, HOSE1-E7/hTERT may provide a novel model system with which to investigate the mechanisms of early molecular changes.

Synchronous endometrioid carcinomas of the uterine corpus and ovary: alterations in the beta-catenin (CTNNB1) pathway are associated with independent primary tumors and favorable prognosis

Diagnosis of synchronous endometrioid carcinomas of the uterine corpus and ovary as either separate independent primary or as metastatic tumors requires careful consideration of a number of gross and histological features. Although such assessment is often sufficient, recent evidence has suggested that molecular analysis may facilitate the diagnosis in problematic cases. Furthermore, as independent synchronous tumors limited to the uterus and ovary are generally associated with favorable outcome, determination of genetic alterations associated with this group of neoplasms may indicate molecular markers of less aggressive behavior. We examined 12 cases of synchronous carcinomas of the uterus and ovary, correlating conventional gross and histological parameters with molecular genetic alterations common to single endometrioid carcinomas occurring in these sites. We identified a frequency of molecular alterations in both independent and metastatic tumors, including microsatellite instability (uterine tumors, 50% and 67%, respectively; ovarian tumors, 33% and 67%) and PTEN mutations (uterine tumors, 38% and 100%; ovarian tumors, 33% and 83%) that is higher than that observed in single sporadic tumors. Loss of heterozygosity for chromosome 17p and 10q was also frequently observed. Nuclear immunoreactivities for beta -catenin and CTNNB1 mutations were restricted to independent uterine and ovarian tumors and were absent in all of the metastatic tumors, providing direct evidence for a divergence of molecular oncogenetic mechanisms in the subset of synchronous endometrioid carcinomas. Furthermore, our data show that molecular genetic classification of synchronous independent versus metastatic tumors based on beta -catenin expression/mutation correlates with clinical outcome.

No significant role for beta tubulin mutations and mismatch repair defects in ovarian cancer resistance to paclitaxel/cisplatin

Background

The mechanisms of chemoresistance in ovarian cancer patients remain largely to be elucidated. Paclitaxel/cisplatin combination is the standard chemotherapeutic treatment for this disease, although some patients do not respond to therapy. Our goals were to investigate whether TUBB mutations and mismatch repair defects underlie paclitaxel and cisplatin resistance.

Methods

Thirty-four patients with primary ovarian carcinomas (26 serous and eight clear cell carcinomas) treated with paclitaxel/cisplatin were analysed. TUBB exon 4 was analysed by nested PCR after a first round PCR using intronic primers. Microsatellite analysis was performed with the quasimonomorphic markers BAT 26 and BAT 34.

Results

Twenty-two of the 34 ovarian cancers (64.7%) presented residual tumour after surgery, seven of which (7/22; 31.8%) were shown to be chemoresistant (five serous and two clear cell tumours). Sequence analysis did not find any mutation in TUBB exon 4. Microsatellite instability was not detected in any of the ovarian carcinomas.

Conclusion

We conclude that TUBB exon 4 mutations and mismatch repair defects do not play a significant role in paclitaxel/cisplatin resistance.

Histologic Type, Organ of Origin, and Wnt Pathway Status: Effect on Gene Expression in Ovarian and Uterine Carcinomas

PURPOSE

Ovarian and uterine carcinomas manifest several differentiation patterns resembling those seen in nonneoplastic epithelia of the gynecologic tract. Specific oncogene and tumor suppressor gene defects have been associated with particular differentiation patterns in carcinomas arising in either the uterus or ovary. For instance, ovarian and uterine carcinomas with endometrioid differentiation frequently show beta-catenin mutations. Whereas type of differentiation is considered in the treatment of uterine carcinomas, it does not presently contribute to decisions about treatment of ovarian carcinomas. A widely accepted view is that the accumulation of specific gene defects and gene expression changes underlies phenotypic traits of cancers, including their response to treatment.

EXPERIMENTAL DESIGN

Using oligonucleotide microarrays to assess gene expression in 103 primary ovarian and uterine carcinomas, we sought to address whether organ of origin or type of differentiation (histotype; endometrioid versus serous) had a more substantial effect on gene expression patterns.

RESULTS

We found that effects on gene expression due to organ of origin and histotype are similar in magnitude and are parallel in that organ effects are similar in the two histotypes and histotype effects are similar in the two organs. In addition, ovarian and uterine endometrioid adenocarcinomas with beta-catenin defects show a common gene expression signature largely distinct from that seen in tumors lacking such defects.

CONCLUSIONS

Our results illustrate how organ of origin, type of differentiation, and specific molecular defects all contribute to gene expression in the most common types of ovarian and uterine cancers. The findings also imply gene expression data will be of value for stratifying ovarian cancer patients for new treatment approaches.

Molecular genetic alterations in endometrioid carcinomas of the ovary: similar frequency of beta-catenin abnormalities but lower rate of microsatellite instability and PTEN alterations than in uterine endometrioid carcinomas

Endometrioid carcinomas of the ovary closely resemble their uterine counterparts. It has been suggested that the former tumors have the same molecular alterations (microsatellite instability [MSI], PTEN, and beta-catenin) described in endometrioid carcinomas of the uterus. We analyzed 55 ovarian carcinomas, including 22 endometrioid, 18 clear cell, and 15 mixed types. MSI was detected in 5 of 39 cases (13%). MLH1 promoter hypermethylation was identified in 2 of the 5 MSI-positive tumors. PTEN was mutated in 5 of 54 cases (9%); of these, 3 had MSI and exhibited frameshift mutations in short-coding mononucleotide repeats. Beta-catenin nuclear expression was detected in 11 of 54 cases (20%) by immunostaining; of these, 7 exhibited CTNNB1 gene mutations. These alterations were found more frequently in endometrioid carcinomas than in tumors of the other 2 groups. Among the former tumors, MSI was detected in 3 of 17 cases (17.5%); PTEN mutations, in 3 of 21 (14%); and beta-catenin, in 8 of 21 (38%). The molecular alterations were found more often in tumors associated with endometriosis than in tumors without endometriosis. Six endometrioid tumors demonstrating matrix metalloproteinase-7 (MMP-7) immunoreactivity with nuclear accumulation of beta-catenin had good outcomes, in contrast to poor outcomes in 7 of 9 predominantly nonendometrioid tumors demonstrating expression of MMP-7 only. We found a similar frequency of beta-catenin abnormalities but lower rates of MSI and PTEN alterations than in uterine endometrioid carcinomas. Alterations in beta-catenin and PTEN genes, as well as MSI, are frequent in low-stage ovarian carcinomas of endometrioid type that have a favorable prognosis.

Evidence that both genetic instability and selection contribute to the accumulation of chromosome alterations in cancer

Cancer cells contain many genetic alterations, and genetic instability may be important in tumourigenesis. We evaluated 58 breast and ovarian cancer cell lines for microsatellite instability (MSI) and chromosomal instability (CIN). MSI was identified in 3/33 breast and 5/25 ovarian cell lines, and 7/8 MSI lines showed an inactivation of mismatch repair. Average ploidy by centromeric fluorescence in situ hybridization (FISH) of MSI (n = 8, average ploidy = 2.65) and microsatellite stable (MSS; n = 7, average ploidy = 3.01) cell lines was not different, due to the presence of three aneuploid MSI lines, and two near-diploid MSS lines. However, the variability of the centromeric FISH data was different between MSI and MSS (P = 0.049). The complexity of structural chromosomal rearrangements was not different between MSI and MSS. Thus, MSI and numerical CIN are not mutually exclusive, and structural CIN occurs independently of MSI or numerical CIN. Dynamic genetic instability was evaluated in three cell lines-MSI diploid (MT-3), MSS diploid (SUM159) and MSS aneuploid (MT-1). Ten clones of each of these cell lines were analysed by centromeric FISH and six-colour chromosome painting. The variation in chromosome number was different among all three cell lines (P < 0.001). MT-3 appeared numerically constant (94% of centromeric FISH signals matched the mode). SUM159 was 88% constant; however, 7% of cells had duplicated chromosomes. MT-1 was 82% constant; most changes were chromosomal losses. The six-colour FISH data showed that SUM159 had more stable structural chromosomal alterations (e.g. chromosomal translocations) compared with MT-3 and MT-1, but had no increase in unstable changes (e.g. chromatid breaks) when compared with MT-3. MT-1 had fewer unstable changes than both MT-3 and SUM159. These data suggest that numerical CIN may contribute to aneuploidy, but that selection plays an important role, particularly for the accumulation of structural chromosomal changes.

Frequent microsatellite instability in synchronous ovarian and endometrial adenocarcinoma and its usefulness for differential diagnosis

Synchronous tumors of the ovary and endometrium are a well-known phenomenon. There are histological criteria for defining double primary tumors or metastasis from one organ to another, but in some cases a precise diagnosis is difficult. In this study we reviewed 17 cases of synchronous ovarian and endometrial adenocarcinoma by previously reported histological criteria and performed a microsatellite analysis, combined with X-linked clonality analysis. We also analyzed 8 cases of endometrial adenocarcinoma with pelvic lymph node metastasis as a control. Five dinucleotide microsatellite markers were selected, and microsatellite analysis was performed by a high-resolution method using fluorescence-labeled polymerase chain reaction and laser scanning. In synchronous tumors, 11 ovarian carcinomas (65%) and 10 endometrial carcinomas (59%)demonstrated microsatellite instability (MSI). In total, 13 of the 17 patients demonstrated MSI in the ovarian tumor, the endometrial tumor, or both. Four cases of endometrial carcinoma with pelvic lymph nodes metastases displayed MSI, and MSI findings of the endometrial tumor and lymph node metastasis were same in all cases. Based on these findings, we considered that similar MSI findings indicate metastatic tumors. According to the MSI findings, 13 of the 17 patients (76%) had single or double clonal tumors, 11 (67%) with double primary tumors and 2 (13%) with metastatic tumors. Using X-linked clonality analysis, 3 patients were diagnosed with double primary tumors. The molecular diagnosis corresponded with the histological criteria in all but 1 case. In conclusion, using both MSI and X-linked clonality analysis, most patients (82%) could be diagnosed as having single or double clonal tumors. The histological criteria are accurate and useful in most cases; however, in some cases where the relationship between the 2 tumors is difficult to determine, high-resolution MSI analysis may be helpful.

Genotyping possible polymorphic variants of human mismatch repair genes in healthy Korean individuals and sporadic colorectal cancer patients

The genotypic consequences of numerous single-nucleotide variants in human mismatch repair genes are mostly undetermined. We examined 27 reported single-nucleotide variants, rarely or ambiguously verified in a population-based study, to identify single-nucleotide polymorphisms (SNPs), haplotypes, and the genotype-phenotype association in Korean populations of 330 healthy individuals, 107 sporadic colorectal cancer patients, and 107 of their first-degree relatives. Real-time PCR 5'-nuclease assays (TaqMan) MGB assay) were used to determine 24 single-nucleotide variants, and restriction fragment length polymorphism (RFLP) assays were used to determine 3 variants. Of these 27 variants, 4 (hMSH2 gIVS12-6, hMLH1 655, hMLH1 1151, and hMSH2 1168, in descending order) were identified as SNPs occurring in 4.5 to 53.1% of healthy individuals, with polymorphism levels of 0.023-0.3 (mean, 0.092). East Asian populations had an ethnic predilection for the hMLH1 1151 SNP. The genotype distribution for all four SNPs showed no association with sporadic colorectal cancer. Twenty-three variants were not identified in the Korean population, suggesting that fifteen of these variants are colorectal cancer-related mutations and eight are SNPs. Two haplotype patterns existed exclusively, but with rare frequency, in sporadic colorectal cancer patients. The hMLH1 655 allele was closely correlated with hMLH1 protein expression (P = 0.02), but none of the four SNPs was associated with clinicopathologic variables. Among the 27 single nucleotide variants of mismatch repair genes, 12 were suggestive of nonfunctional SNPs and 15 may be colorectal cancer-related mutations. Further verification in other ethnic groups may provide the genotypic and phenotypic significance of single nucleotide variants found in mismatch repair genes.

Genotyping possible polymorphic variants of human mismatch repair genes in healthy Korean individuals and sporadic colorectal cancer patients

The genotypic consequences of numerous single-nucleotide variants in human mismatch repair genes are mostly undetermined. We examined 27 reported single-nucleotide variants, rarely or ambiguously verified in a population-based study, to identify single-nucleotide polymorphisms (SNPs), haplotypes, and the genotype-phenotype association in Korean populations of 330 healthy individuals, 107 sporadic colorectal cancer patients, and 107 of their first-degree relatives. Real-time PCR 5'-nuclease assays (TaqMan) MGB assay) were used to determine 24 single-nucleotide variants, and restriction fragment length polymorphism (RFLP) assays were used to determine 3 variants. Of these 27 variants, 4 (hMSH2 gIVS12-6, hMLH1 655, hMLH1 1151, and hMSH2 1168, in descending order) were identified as SNPs occurring in 4.5 to 53.1% of healthy individuals, with polymorphism levels of 0.023-0.3 (mean, 0.092). East Asian populations had an ethnic predilection for the hMLH1 1151 SNP. The genotype distribution for all four SNPs showed no association with sporadic colorectal cancer. Twenty-three variants were not identified in the Korean population, suggesting that fifteen of these variants are colorectal cancer-related mutations and eight are SNPs. Two haplotype patterns existed exclusively, but with rare frequency, in sporadic colorectal cancer patients. The hMLH1 655 allele was closely correlated with hMLH1 protein expression (P = 0.02), but none of the four SNPs was associated with clinicopathologic variables. Among the 27 single nucleotide variants of mismatch repair genes, 12 were suggestive of nonfunctional SNPs and 15 may be colorectal cancer-related mutations. Further verification in other ethnic groups may provide the genotypic and phenotypic significance of single nucleotide variants found in mismatch repair genes.

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.

Pathophysiological Dynamics of Human Ovarian Surface Epithelial Cells in Epithelial Ovarian Carcinogenesis

Epithelial ovarian cancer is responsible for almost half of all the deaths from female genital tract tumors. Major impediments to the clinical treatment of this disease are the relatively asymptomatic progression and a lack of knowledge regarding defined precursor or malignant lesions. Most epithelial ovarian cancers are thought to arise from the transformation of ovarian surface epithelial cells, a single continuous layer of flat-to-cuboidal mesothelial cells surrounding the ovary. To improve our understanding of the pathogenesis of epithelial ovarian cancer, it is necessary to study the biological characteristics of normal ovarian surface epithelial cells. However, this approach has been hampered by the inability to purify and culture such human cells. During the past decade, procedures to isolate and culture human ovarian surface epithelial cells have been developed, and, subsequently, using viral oncogenes, several immortalized cells have been established. This new experimental system is being employed to improve our understanding of the genetic changes leading to the initiation of epithelial ovarian cancer and to identify events in the cancer's development. This review mainly describes the biological dynamics of ovarian surface epithelial cells in the pathogenesis of epithelial ovarian cancer, focusing on humans and excluding small animal models.

Microsatellite instability and expression of hMLH1 and hMSH2 proteins in ovarian endometrioid cancer

Microsatellite instability and loss of heterozygosity has been implicated in ovarian carcinogenesis. The reported frequency of microsatellite instability in human ovarian cancer varies significantly owing to the use of heterogeneous tumor histotypes and various microsatellite markers in different laboratories. In this study, we determined the frequency of microsatellite instability in 74 ovarian endometrioid carcinomas using four microsatellite markers (BAT25, BAT26, D5S346, D17S250), and examined hMLH1 and hMSH2 protein expression. In all, 20% of the tumors were microsatellite instability high (two or more markers showing instability) and 12% were microsatellite instability low (one marker showed instability). Loss of hMLH1 and/or hMSH2 expression was found in nine of 15 microsatellite instability-high tumors. The microsatellite instability-high phenotype tended to occur more frequently in low-grade tumors (P=0.053), but did not correlate with clinical stage. Totally, 38% of cases also displayed loss of heterozygosity at D17S250; this loss of heterozygosity was associated with high clinical stage (P=0.097). Our results indicate that both microsatellite and loss of heterozygosity at D17S250 are involved in the development of ovarian endometrioid carcinoma.

Mismatch repair gene expression defects contribute to microsatellite instability in ovarian carcinoma

BACKGROUND

hMLH1, the human MutL homologue, has been linked to microsatellite instability (MSI) in gastrointestinal tumors. However, to the authors' knowledge, the role of hMLH1, the other mismatch repair genes (MMR), and MSI in ovarian carcinoma has not been well defined. The purpose of the current study was to determine the relation between MSI of ovarian carcinoma and MMR gene expression, hMLH1 and hMSH2 hypermethylation, and hMLH1 and hMSH2 null mutations.

METHODS

hMLH1 mRNA was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) and amplification of cDNA using a housekeeping gene (glycerol 3-phosphate dehydrogenase) as a control for mRNA quality and quantity. Methylation-specific PCR (MS-PCR) was used to correlate methylation of the hMLH1 and hMSH2 CpG islands with mRNA expression status. Similar techniques were used to evaluate the concomitant expression of five other MMR: hMSH2, hMSH3, hMSH6, PMS1, and PMS2. Microsatellite instability was studied using the National Cancer Institute consensus markers (D2S123, D5S346, D17S250, BAT25, and BAT26) and NM23 as described previously.

RESULTS

One hundred twenty-five primary tumors were analyzed. High-frequency MSI (MSI-H) was found in 21 tumors (16.8%). hMLH1 mRNA was absent in 10 of these 21 tumors (47.6%). In each case, coordinated hypermethylation of both regions A and C of the promoter was identified. Microsatellite stable and low-frequency MSI tumors all were found to express not only hMLH1 but the other MMR genes as well (P < 0.001). Absence of expression of hMSH2 and the four other MMRs occurred in tumors with absent hMLH1 mRNA expression because of CpG island hypermethylation. No absence of expression of hMSH2, hMSH3, hMSH6, PMS1, or PMS2 was found to occur in tumors expressing hMLH1. None of the 11 MSI-H tumors without promoter hypermethylation demonstrated a null mutation in hMLH1 or hMSH2.

CONCLUSIONS

A molecular mechanism to explain > 50% of the MSI-H phenotype in ovarian carcinoma cases was demonstrated. MSI-H may occur because of MMR defects, especially hMLH1 promoter hypermethylation. Additional mechanisms are required to explain the balance between the cases of MSI-H as well as the phenomenon of MSI-L tumors.

Genetic alterations in ovarian carcinoma: with specific reference to histological subtypes

Multiple genetic changes including activation of proto-oncogenes and inactivation of tumor suppressor gene are involved in the development of human ovarian cancer. We describe such genetic alterations with specific reference to histological subtypes. K-ras activation is specific for mucinous tumors including adenomas. Borderline tumors and carcinomas, suggesting that K-ras activation may be associated with the mucinous differentiation rather than malignant transformation. Inactivation of p53 is detected in 30-40% of ovarian carcinoma. Mutations are more frequently observed in serous carcinomas, but not found in adenomas or rarely found in borderline tumors, suggesting that p53 mutations may be directly involved in malignant transformation. TGFbeta-2 mutations are found in 50% of endometrioid carcinoma, but rarely in other type. Loss of DCC mRNA expression is found in 50% of serous carcinomas but less frequently in other type. Loss of DCC expression is rare in borderline tumors and adenomas, suggesting that inactivation of DCC may be directly involved in malignant transformation. Microsatellite instability (MI) is found in 17% of ovarian carcinomas, and is frequently found in endometrioid carcinomas. Although inactivation of p16 by point mutation or deletion is rare, p16 inactivation by loss of expression is relatively common.

The clinical importance and prognostic implications of microsatellite instability in sporadic cancer

AIMS

The genetic abnormality known as microsatellite instability (MSI), first identified in colorectal cancer in 1993, has subsequently been recognised in other malignancies. These cancers are caused by a defect in the nuclear mismatch repair system, allowing mutations to accumulate with every cellular division. Hereditary Non Polyposis Colon Cancers (HNPCC) and associated malignancies demonstrating MSI have a unique histological appearance, improved prognosis and altered response to chemotherapy and radiotherapy. This review examines the incidence of MSI and its clinical significance in commonly occurring solid malignancies.

METHOD

A medline based literature search was performed using the key words 'Microsatellite Instability' and the name of the specific malignancy being investigated. Additional original papers were obtained from citations in those articles identified in the original medline search.

RESULTS

MSI has been detected in many solid malignancies although the definition of instability applied has been variable. It is most commonly found in sporadic malignancies that also occur in the HNPCC syndrome such as colorectal, stomach, endometrial and ovarian cancer. MSI may impart a favorable prognosis in colorectal, gastric, pancreatic and probably oesophageal cancers but a poor prognosis in non small cell lung cancer. In clinical studies colorectal cancers demonstrating MSI respond better to chemotherapy while in vitro studies using MSI positive cell lines show resistance to radiotherapy and chemotherapy.

CONCLUSION

MSI may be a useful genetic marker in prognosis and could be an influential factor in deciding treatment options. However, in many cancers its significance remains unclear and more evaluation is required.

Genetic alterations in ovarian cancer cells that might account for sensitivity to chemotherapy in patients

The cellular response to anticancer agent treatments is determined by many factors that could be altered in tumor cells. The induction of apoptosis of cancer cells is thought to be important for the overall response of these cells. Despite the introduction of new and potent anticancer agents, the survival rate for patients with ovarian cancer remains poor. In general ovarian cancer cells present a poor propensity to undergo apoptosis, which could be one of the reasons for this relatively poor response observed in the clinic. Induction of apoptosis is the result of activation and repression of pro- and antiapoptotic genes, which are regulated by complex mechanisms. Many cancer cells activate a "survival" program to escape disruption and allow propagation. In this review we have analyzed the role of genetic alterations observed in ovarian cancer cells in determining cellular response to drug treatment.

Microsatellite instability and its relevance to cutaneous tumorigenesis

Increasing evidence suggests that human tumors sequentially accumulate multiple mutations that cannot be explained by the low rates of spontaneous mutations in normal cells (2-3 mutations/cell). The mathematical models estimate that for the solid tumors to develop, as many as 6-12 mutations are required in each tumor cell. Therefore, to account for such high mutation rates, it is proposed that tumor cells are genetically unstable, i.e. they have genome-wide mutations at short repetitive DNA sequences called microsatellites. Microsatellite repeats are scattered throughout the human genome, primarily in the non-coding regions, and can give rise to variants with increased or reduced lengths, i.e. microsatellite instability (MSI). This instability has been reported in an increasing number of cutaneous tumors including: melanocytic tumors, basal cell carcinomas and primary cutaneous T-cell lymphomas. Moreover, MSI has been observed in skin tumors arising in the context of some hereditary disorders such as Muir-Torre syndrome, Von Recklinghausen's disease and disseminated superficial porokeratosis. While MSI in some of these disorders reflects underlying DNA replication errors, the mechanism of instability in others is still unknown. Thus far, MSI is considered to be a distinct tumorigenic pathway that reveals surprising versatility. The ramifications for cutaneous neoplasms warrant further investigation.

Risk assessment & genetic testing

Ovarian cancer is the fifth most common cause of cancer death in women in Western countries and family history is one of the strongest known risk factors. Approximately 5 to 13% of all ovarian cancer cases are caused by the inheritance of cancer predisposing genes with an autosomal pattern of transmission. The inherited fraction of ovarian cancer may differ between populations. Based on analysis of familial ovarian cancer pedigrees and other epidemiological studies, three hereditary ovarian cancer syndromes have been defined. The identification of the genes responsible for most hereditary ovarian cancers has open a new area of early detection methods and preventive procedures specifically dedicated to women identified as carrying ovarian cancer predisposing genes. Predictive oncology is best performed by a dedicated unit with professionals aware of all the issues surrounding genetic testing.

Microsatellite instability, MLH-1 promoter hypermethylation, and frameshift mutations at coding mononucleotide repeat microsatellites in ovarian tumors

BACKGROUND

Microsatellite instability (MI) is frequent in endometrial carcinomas (ECs), but its occurrence in ovarian tumors is uncertain. Microsatellite instability positive ECs frequently are associated with frameshift mutations in coding mononucleotide tracts in IGFIIR, BAX, hMSH6, and hMSH3.

METHODS

DNA from 52 consecutive patients with ovarian tumors (10 benign, 7 borderline, and 35 malignant) was obtained from neoplastic and normal tissue. After preliminary results, the series was expanded by including 41 additional, previously selected, endometrioid and clear cell carcinomas. Microsatellite instability analysis was assessed by evaluating three (CA)n dinucleotide repeats (D2S123, D5S346, D17S250) and two mononucleotide tracts (BAT 25 and BAT 26). Frameshift mutations at coding mononucleotide repeats (IGFIIR, TGF beta II, BAX, hMSH6, and hMSH3) were investigated by single-strand conformation polymorphism analysis and DNA sequencing. MLH-1 methylation was assessed by methylation specific PCR.

RESULTS

Microsatellite instability was identified in only 2 of the 52 (3.8%) tumors of the initial series (1 endometrioid and 1 clear cell carcinoma). After expanding the initial series of 15 endometrioid and clear cell carcinomas with 41 additional endometrioid and clear cell carcinomas, MI was found in 7 of the total series of 56 endometrioid and clear cell carcinomas (12.5%). Frameshift mutations in coding mononucleotide tracts were detected in BAX (6 of 7), IGFIIR (1 of 7), and MSH3 (2 of 7). MLH-1 promoter hypermethylation was identified in three of six MI positive tumors.

CONCLUSIONS

Microsatellite instability was infrequent in this series of ovarian tumors, and it was limited to endometrioid and clear cell carcinomas. Like EC, many ovarian carcinomas with MI follow the same process of MLH-1 promoter methylation and accumulation of mutations in coding mononucleotide tracts.