New insights on the pathogenesis of ovarian carcinoma: molecular basis and clinical implications

Ovarian carcinoma can be subdivided into two categories termed type I and type II. Type I tumours, usually having an indolent clinical behaviour, are often detected in early stage, and rarely harbour p53 gene mutations. Each histological type has a distinct molecular profile with mutations of genes involved in different signalling transduction pathways, such as KRAS, BRAF, CTNNB1, PTEN, PIK3CA and ARID1A. Type II tumours, accounting for 75% of the cases, have a very aggressive biological behaviour, are usually in advanced stage at presentation, harbour p53 gene mutations in 80% of the cases, and sometimes have alterations of homologous recombination (HR). Both type I and type II tumours arise from extra-ovarian precursors. Serous carcinomas derive from tubal epithelium, endometrioid and clear cell carcinomas from endometrial tissue, and mucinous and Brenner tumours from transitional epithelial cells located near the tubo-peritoneal junction. These new concepts on the pathogenesis of ovarian carcinoma could deeply modify both the preventive approach in women with germ-line BRCA(1) or BRCA(2) mutations and the treatment of patients with advanced or recurrent disease. For instance, BRAF inhibitors could be used in low-grade serous carcinomas, PIK3CA inhibitors could be employed in clear cell carcinoma, and poly (ADP-ribose) polymerase inhibitors could be used not only in hereditary ovarian carcinoma but also in non-hereditary, high-grade serous ovarian carcinoma which sometimes shows defective HR.     

Comparative proteomics of ovarian epithelial tumors

We analyzed 12 ovarian epithelial tumors using 2D PAGE-based comparative proteomics to construct intra- and inter-tumoral distance map trees and to discover surrogate biomarkers indicative of an ovarian tumor. The analysis was performed after laser microdissection of 12 fresh-frozen tissue samples, including 4 serous, 5 mucinous, and 3 endometrioid tumors, with correlation with their histopathological characteristics. Ovarian epithelial tumors and normal tissues showed an apparent separation on the distance map tree. Mucinous carcinomas were closest to the normal group, whereas serous carcinomas were located furthest from the normal group. All mucinous tumors with aggressive histology were separated from the low malignant potential (LMP) group. The benign-looking cysts adjacent to the intraepithelial carcinoma (IEC) showed an expression pattern identical to that of the IEC area. The extent of change on the lineages leading to the mucinous and serous carcinoma was 1.98-fold different. The overall gene expression profiles of serous or endometrioid carcinomas appeared to be less affected by grade or stage than by histologic type. The potential candidate biomarkers screened in ovarian tumors and found to be significantly up-regulated in comparison to normal tissues were as follows: NM23, annexin-1, protein phosphatase-1, ferritin light chain, proteasome alpha-6, and NAGK (N-acetyl glucosamine kinase). In conclusion, ovarian mucinous tumors are distinct from other ovarian epithelial tumors. LMP mucinous tumors showing histologically aggressive features belong to mucinous carcinoma on the proteomic basis.     

Effects of tamoxifen on the endometrium and its mechanism of carcinogenicity

This study was conducted to clarify the clinicopathological characteristics of tamoxifen-associated endometrial carcinomas and its mechanisms of carcinogenesis. Seven patients with tamoxifen-associated endometrial carcinomas (TAM group) and 28 with sporadic endometrioid adenocarcinomas (EMC group) were included in the study. The clinicopathological factors, such as FIGO stage, histological type, grade, lymph node metastases, vascular invasion and the coexistence of hyperplasia, were investigated in both groups. The protein expression of p53, PTEN, hMLH1 and hMSH2 was investigated by immunohistochemistry. Microsatellite instability (MSI), k-ras and p53 mutation were also examined. In the TAM group, the histological types included five endometrioid, one endometrioid combined with serous and one clear cell type. The rates of coexistence with hyperplasia (five of seven cases) and vascular invasion (four cases) were significantly higher in the TAM group. The rates of stage III/IV (four cases) and lymph node metastasis (three cases) tended to be higher in the TAM group. Although there were no significant differences in PTEN, hMLH1 and hMSH2 expression between the two groups, p53 mutation was more frequent in three out of five cases (60%) in the TAM group compared with 2 of 15 cases in the EMC group (13.3%). No significant differences were observed concerning MSI and k-ras mutation in either group. These results suggested that TAM-associated endometrial carcinomas have overlapping biological characteristics of type I and type II endometrial carcinomas. This might explain the somewhat worse prognosis of these tumors than sporadic endometrioid carcinomas.     

Clear cell carcinoma in a background of endometriosis. Case report of a finding in a midline abdominal scar 5 years after a total abdominal hysterectomy

BACKGROUND: Endometriosis is considered a premalignant process whose association with carcinoma is well documented. We discuss a case of clear cell carcinoma with an unusual presentation in that it was located outside the abdominal cavity and was the only lesion noted clinically and radiologically. The histopathologic diagnostic criteria will be reviewed, as will the association of carcinomas with endometriosis. Furthermore, we will review the current literature of extraovarian clear cell carcinoma associated with endometriosis with regard to clinical outcome. CASE: A 42-year-old Hispanic woman presented to the Fine Needle Aspiration (FNA) Clinic at Parkland Hospital, Dallas, Texas, in August 2005 secondary to a growing area of firmness associated with her midline abdominal hysterectomy scar. A single mass anterior to the abdominal wall was identified radiologically. The FNA sample was reported as highly atypical cells suspicious for adenocarcinoma. Excision of this mass revealed a clear cell carcinoma in a background of endometriosis. CONCLUSION: Clear cell carcinoma is one of the most prevalent carcinomas associated with endometriosis, whether identified in the ovary or extraovarian site. This case is perplexing because the mass was a solitary lesion and the patient never had documented endometriosis. The unusual presentation may make survival difficult to predict.     

Role of K-ras and Pten in the development of mouse models of endometriosis and endometrioid ovarian cancer

Epithelial ovarian tumors present a complex clinical, diagnostic and therapeutic challenge because of the difficulty of early detection, lack of known precursor lesions and high mortality rates. Endometrioid ovarian carcinomas are frequently associated with endometriosis, but the mechanism for this association remains unknown. Here we present the first genetic models of peritoneal endometriosis and endometrioid ovarian adenocarcinoma in mice, both based on the activation of an oncogenic K-ras allele. In addition, we find that expression of oncogenic K-ras or conditional Pten deletion within the ovarian surface epithelium gives rise to preneoplastic ovarian lesions with an endometrioid glandular morphology. Furthermore, the combination of the two mutations in the ovary leads to the induction of invasive and widely metastatic endometrioid ovarian adenocarcinomas with complete penetrance and a disease latency of only 7 weeks. The ovarian cancer model described in this study recapitulates the specific tumor histomorphology and metastatic potential of the human disease.     

Expression and methylation status of 14-3-3 sigma gene can characterize the different histological features of ovarian cancer

We hypothesize that 14-3-3 sigma gene expression and its regulation by methylation can characterize histological types of primary human epithelial ovarian cancer. To test this hypothesis, ovarian cancer cell lines and 54 ovarian cancer tissue samples were analyzed for expression and methylation of 14-3-3 sigma gene using methylation specific PCR. The results of our experiments demonstrate that 14-3-3 sigma gene was methylated and inactivated in ES-2 ovarian cell line, which was derived from clear cell adenocarcinoma. Treatment of this cell line with demethylating agent 5-aza-2'-deoxycytidine restored the expression of 14-3-3 sigma gene. In human ovarian cancer tissues, the expression of 14-3-3 sigma protein was inactivated in most of the ovarian clear cell carcinoma tissues. Interestingly, 14-3-3 sigma protein expression was positive in significantly higher percentages of serous (89.5%), endometrioid (90%), and mucinous (81.8%) ovarian adenocarcinoma tissues. The ovarian clear cell carcinoma samples with inactivated 14-3-3 sigma protein were highly methylated, suggesting that inactivation of 14-3-3 sigma gene is through DNA methylation. Using direct DNA sequencing, 14-3-3 sigma gene methylation on all the 17 CpG sites was significantly higher in ovarian clear cell carcinoma as compared to other histological types of ovarian cancer (serous, endometrioid, and mucinous). This is the first report suggesting that 14-3-3 sigma gene expression and methylation status can characterize histological features of different types of ovarian cancer.     

Spontaneous ovarian tumors in twelve baboons: a review of ovarian neoplasms in non-human primates

Twelve spontaneous ovarian tumors were found in the Southwest Foundation for Biomedical Research baboon colony. These included four granulosa cell tumors, three teratomas, two endometrioid carcinomas, one seromucinous cystadenofibroma, a cystic papillary adenocarcinoma, and an ovarian carcinoma. Age was a pre-disposing factor. With one exception, the tumors of surface epithelial- and sex cordstromal origin occurred in baboons over 17 years of age. The exceptional animal was 7 years of age when a malignant granulosa cell tumor with Sertoli cell differentiation was identified. The two endometrioid tumors, which were found in 17- and 30-year-old animals, were both associated with endometriosis. In contrast, the teratomas, which are tumors of germ cell origin, were found in younger animals, i.e. 17 years of age or younger. One case of an ovarian carcinoma with metastases was observed in a 6-month-old infant. Cases of spontaneous ovarian tumors from the literature are reviewed.     

Detecting and investigating the significance of high-frequency LOH chromosome regions for endometriosis-related candidate genes

To detect the high-frequency loss of heterozygosity (LOH) chromosome regions for ectopic endometrium of ovarian endometriosis (EMs) and to investigate the significance of high-frequency LOH chromosome regions in EMs, we obtained ectopic endometrium by laser capture microdissection (LCM (22 samples)), manual capture microdissection (MCM (18 samples)), and routine dissection (14 samples), respectively. After restriction and circularization-aided rolling circle amplification (RCA-RCA), LOH was detected at 12 microsatellite (MS) loci. The frequency of LOH was 59.09% (13/22) in LCM group, 61.11% (11/18) in the MCM group and 21.43% (3/14) in the routine dissection group. The latter was significantly lower when compared with the former two (p < 0.05). In the LCM group, candidate chromosome regions 17q21.31 and 9p21.3 had LOH frequencies of 23.8 and 13.6%, respectively. The highest LOH frequency was detected at the locus AAAT2 on chromosome 17q21.31 (40%). The chromosome region with the highest frequency of LOH for ectopic endometrium was 17q21.31, especially at the AAAT2 locus, which prompted that down regulation of the candidate genes nearby the locus might be one of the mechanisms of EMs pathogenesis. LCM combined with RCA-RCA is a reliable technique for analyzing endometrial LOH at multiple MS loci. MCM combined with RCA-RCA, which provided similar results, was more cost-effective.     

Density distribution, cytomorphologic features and immunologic characteristics of ovarian and endometrial clear cell carcinomas

Three subpopulations of cancer cells with different morphologic features were separated by density gradient centrifugation of two ascitic fluids and one cystic fluid from one patient with ovarian clear cell carcinoma and one with endometrial clear cell carcinoma. Immunophenotypic analyses of isolated fractions using polyclonal and monoclonal antibodies against ovarian carcinoma-associated antigens revealed significant immunologic heterogeneity among the tumor cells. The identical histopathologic structures of the ovarian and endometrial clear cell carcinomas and the similar distribution and immunologic reactivity of the cell types isolated from the ascitic and cystic fluids confirmed the common histogenesis of both cancers. These findings suggest that the conventional cytologic diagnosis of clear cell carcinomas could be supplemented by immunofluorescent staining. Density gradient centrifugation appeared to be a useful method for the separation of mesothelial cells.     

Differential analysis of ovarian and endometrial cancers identifies a methylator phenotype

Despite improved outcomes in the past 30 years, less than half of all women diagnosed with epithelial ovarian cancer live five years beyond their diagnosis. Although typically treated as a single disease, epithelial ovarian cancer includes several distinct histological subtypes, such as papillary serous and endometrioid carcinomas. To address whether the morphological differences seen in these carcinomas represent distinct characteristics at the molecular level we analyzed DNA methylation patterns in 11 papillary serous tumors, 9 endometrioid ovarian tumors, 4 normal fallopian tube samples and 6 normal endometrial tissues, plus 8 normal fallopian tube and 4 serous samples from TCGA. For comparison within the endometrioid subtype we added 6 primary uterine endometrioid tumors and 5 endometrioid metastases from uterus to ovary. Data was obtained from 27,578 CpG dinucleotides occurring in or near promoter regions of 14,495 genes. We identified 36 locations with significant increases or decreases in methylation in comparisons of serous tumors and normal fallopian tube samples. Moreover, unsupervised clustering techniques applied to all samples showed three major profiles comprising mostly normal samples, serous tumors, and endometrioid tumors including ovarian, uterine and metastatic origins. The clustering analysis identified 60 differentially methylated sites between the serous group and the normal group. An unrelated set of 25 serous tumors validated the reproducibility of the methylation patterns. In contrast, >1,000 genes were differentially methylated between endometrioid tumors and normal samples. This finding is consistent with a generalized regulatory disruption caused by a methylator phenotype. Through DNA methylation analyses we have identified genes with known roles in ovarian carcinoma etiology, whereas pathway analyses provided biological insight to the role of novel genes. Our finding of differences between serous and endometrioid ovarian tumors indicates that intervention strategies could be developed to specifically address subtypes of epithelial ovarian cancer.     

PTEN蛋白的异常表达与卵巢子宫内膜异位症恶变的关系

目的:探讨PTEN蛋白表达与与卵巢子宫内膜异位症(内异症)恶变的关系.方法:应用免疫组化方法检测21例子宫内膜异位症相关卵巢癌(内异症相关卵巢癌),10例不典型卵巢子宫内膜异位症(不典型内异症)及23例内异位症中PTEN蛋白表达.结果:PTEN在内异症和不典型内异症组阳性表达率分别为82.61%和60.00%,内异症相关卵巢癌组中PTEN蛋白阳性表达率为42.86%.内异症相关卵巢癌组PTEN蛋白表达与内异症组相比差异有显著性(p＜0.05). PTEN蛋白表达与内异症相关卵巢癌患者的年龄、病理类型无相关性(p＞0.05),与分化程度、临床分期相关(p＜0.05),在内异症相关卵巢癌中,临床分期早,分化程度高的PTEN表达显著高于分期晚,分化差的.结论:PTEN蛋白表达缺失可能参与了卵巢子宫内膜异位症恶变,有可能成为一个很有潜力的诊断指标及新的治疗靶点而应用于临床.     

PTEN基因和P53基因在子宫内膜癌中的表达及意义

目的:探讨PTEN基因和P53基因在子宫内膜癌中的表达及临床意义,为子宫内膜癌的治疗提供参考依据。方法:用免疫组化法检测50例子宫内膜癌患者PTEN基因缺失和P53基因突变情况,并分析两者与子宫内膜癌不同病理变化的相关性。结果:PTEN缺失24例,缺失率48.00%,进一步研究显示PTEN缺失与细胞分化程度和肌层浸润情况密切相关(P0.05),P53突变32例,缺失率64.00%,并进一步研究显示P53突变与FIGO分期,细胞分化程度和肌层浸润情况密切相关(P0.05)。结论:PTEN基因缺失和P53基因突变与子宫内膜癌发生和发展密切相关,以PTEN基因和P53基因为靶点的生物治疗在进展期内膜癌中的治疗价值值得进一步深入研究。     

PTEN基因和P53基因在子宫内膜癌中的表达及意义

目的：探讨PTEN基因和P53基因在子宫内膜癌中的表达及临床意义,为子宫内膜癌的治疗提供参考依据。方法：用免疫组化法检测50例子宫内膜癌患者PTEN基因缺失和P53基因突变情况,并分析两者与子宫内膜癌不同病理变化的相关性。结果：PTEN缺失24例,缺失率48.00%,进一步研究显示PTEN缺失与细胞分化程度和肌层浸润情况密切相关（P〈0.05）,P53突变32例,缺失率64.00%,并进一步研究显示P53突变与FIGO分期,细胞分化程度和肌层浸润情况密切相关（P〈0.05）。结论：PTEN基因缺失和P53基因突变与子宫内膜癌发生和发展密切相关,以PTEN基因和P53基因为靶点的生物治疗在进展期内膜癌中的治疗价值值得进一步深入研究。     

中国人卵巢上皮性肿瘤nm23H1基因遗传不稳定性的研究

The aim of this study was to examine microsatellite instability (MSI) and loss of heterozygosity (LOH) of locus D17S396 on chromosome 17 and their influence on the expression of nm23H1 in the epithelial ovarian tumors, which may provide experimental basis for the mechanism of nm23H1 gene and tumor metastasis. Techniques such as DNA extraction from formalin-fixed paraffin-embedded tissues, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), ordinary silver stain were used to study MSI and LOH of locus D17S396. Envision immunohistochemistry and Leica-Qwin computer imaging techniques were used to assess the expression of nm23H1 gene. In our experiments, the frequency of heredity instability of malignant ovarian tumors was 40%, which is higher than that of borderline ovarian tumors, while there were no heredity instability occurred in benign ovarian tumors and normal ovarian tissue. Among 25 epithelial ovarian carcinomas, the frequency of LOH in lymph node metastasis cases (66.67%) was significantly higher than those without metastasis (10.53%). Moreover, the frequency of LOH was higher in FIGO stage III and IV than in stage I and II. However, the frequency of MSI showed no correlation with any clinicopathologic characteristics. The positive frequency of nm23H1 protein in the ovarian epithelial carcinoma and borderline tumors were 56.00% and 57.14%, respectively. They were both higher than those of the benign tumors and normal ovarian tissue. In the epithelial ovarian carcinomas, the positive frequency of nm23H1 protein in lymph node metastasis case was significantly lower than those without metastasis. FIGO stage III and IV also exhibited lower positive frequency of nm23H1 protein compared with stage I and II. Furthermore, there was no difference in nm23H1 protein expression intensity analyzed by computer imaging. In the epithelial ovarian carcinomas, the positive frequency of nm23H1 protein in LOH positive group was 0.00%, which is lower than that of LOH negative group (P < 0.01). The results indicated that the heredity instability of nm23H1 gene might be implicated in pathogenesis and progression of epithelial ovarian tumor. The occurrence of LOH might be the molecule marker of the deteriorism of ovarian tissue. Both MSI and LOH of nm23H1 gene controlled development of the epithelial ovarian tumor independently in different paths. LOH could inhibit the expression of nm23H1 in local tissue of the epithelial ovarian carcinoma, which endowed it with high aggressive and poor prognosis. Increasing the amount of nm23H1 protein expression could effectively restrain metastasis of the ovarian epithelial carcinoma and improve prognosis of patients.     

Pap smears in women with endometrial carcinoma

OBJECTIVE: To correlate Pap smear findings with the histology of endometrial carcinoma and stage of the disease. STUDY DESIGN: Between 1995 and 1998, 76 women with endometrial carcinoma, having had Pap smears done within two to three months of hysterectomy at Memorial Sloan-Kettering Cancer Center, formed the basis for this study. All Pap smears and histologic sections were reviewed. RESULTS: Thirty-four patients had normal Pap smears (45%), and 42 had abnormal ones (55%). The mean age of the two groups was 65.1 and 65.2 years, respectively. Histologic subtypes included 44 International Federation of Gynecology and Obstetrics (FIGO) grade 1 endometrioid adenocarcinoma (low grade) and 32 high grade carcinomas, including 19 FIGO grade 2 or 3 endometrioid adenocarcinomas, 5 papillary serous carcinomas (PSC), 2 clear cell carcinomas (CC), 1 adenosquamous carcinoma, 3 endometrioid adenocarcinomas mixed with PSC and 2 endometrioid adenocarcinomas mixed with CC. The proportions of patients with low and high grade tumors with abnormal Pap smears were 43% (19/44) and 72% (23/32), respectively (P=.01). The proportions of patients with abnormal Pap smears and no myometrial invasion, invasion of <50% and >50% myometrial thickness were 40% (8/20), 62% (26/42) and 57% (8/14), respectively (P =.27). Vascular invasion was identified in 56% (9/16) of patients with abnormal Pap smears and in 55% (33/60) of patients with normal ones (P = .93). The proportions of patients having abnormal Pap smears with stage I and stages II, III or IV disease were 48% (30/62) and 86% (12/14), respectively (P =.01). CONCLUSION: Although the Pap smear is not a sensitive screening test for endometrial cancer and a negative Pap smear does not rule it out, this study revealed that abnormal Pap smears are significantly associated with high grade of tumor and stage II-IV endometrial carcinoma. However, they are not associated with patient age, depth of myometrial invasion or vascular invasion.     

Gene expression patterns in ovarian carcinomas

We used DNA microarrays to characterize the global gene expression patterns in surface epithelial cancers of the ovary. We identified groups of genes that distinguished the clear cell subtype from other ovarian carcinomas, grade I and II from grade III serous papillary carcinomas, and ovarian from breast carcinomas. Six clear cell carcinomas were distinguished from 36 other ovarian carcinomas (predominantly serous papillary) based on their gene expression patterns. The differences may yield insights into the worse prognosis and therapeutic resistance associated with clear cell carcinomas. A comparison of the gene expression patterns in the ovarian cancers to published data of gene expression in breast cancers revealed a large number of differentially expressed genes. We identified a group of 62 genes that correctly classified all 125 breast and ovarian cancer specimens. Among the best discriminators more highly expressed in the ovarian carcinomas were PAX8 (paired box gene 8), mesothelin, and ephrin-B1 (EFNB1). Although estrogen receptor was expressed in both the ovarian and breast cancers, genes that are coregulated with the estrogen receptor in breast cancers, including GATA-3, LIV-1, and X-box binding protein 1, did not show a similar pattern of coexpression in the ovarian cancers.     

Selective gene expression profiling of mTOR-associated tumor suppressor and oncogenes in ovarian cancer

The aim of this study was to selectively profile the activation status of mammalian target of rapamycin (mTOR)-associated oncogenes and tumor suppressor genes (TSGs) in ovarian cancer specimens, healthy ovaries and benign ovarian tumors, including endometrial cysts. We used a novel type of microfluidic gene array to examine the expression of 15 human tumor suppressors and oncogenes in ovarian cancer specimens of 53 patients, benign ovarian cysts of 29 women (endometrial and simple) and 11 healthy ovaries of individuals in whom the material was obtained during total hysterectomies performed because of fibroid changes. The array was custom-designed to include the following genes: NF1, RHEB, mTOR1, AKT-1, PTEN, TSC1, TSC2, KRAS, RPS6KB1, 4EBP1, TP53, EIF4E, STK11, PIK3CA and BECN1. Confirmatory immunohistochemical detection was performed for a group of selected proteins. Particularly significant differences were observed as to the expression of PTEN (p < 0.0001), TP53 (p = 0.0003), PIK3CA (p = 0.0003) and BECN1 (p = 0.0014) which were shown to be downregulated in cancer patients when compared to healthy ovaries and benign ovarian cysts (endometrial and simple). These markers did not show association with grade or stage of the tumor. Immunohistochemistry showed that PTEN, TP53, PIK3CA and BECN1 proteins are expressed in ovarian cancer. Our results indicate that there are significant differences in the expression of some of the mTOR-related tumor suppressors and oncogenes which could be associated with the pathogenesis of ovarian cancer.     

Molecular pathology of endometrial carcinoma: transcriptional signature in endometrioid tumors

A dualistic model, which has been established on a morphological basis and that differentiates type I endometrioid from type II non-endometrioid endometrial cancer, is widely accepted. Molecular genetics have provided us with data supporting the dualistic model of endometrial tumorigenesis and with some clues to speculate about the sequence of the molecular alterations defining the tumorigenesis pathways. In type I endometrioid endometrial cancer, PTEN gene silencing, microsatellite instability associated with defects in DNA mismatch repair genes, or mutations in the K-ras gene are the known major alterations defining the progression from normal endometrium to hyperplasia and then on to carcinoma. Recently, cDNA microarray technology for identifying the differences in gene expression patterns between the histological types of endometrial cancer have permitted the identification of differentially expressed genes that could help us to understand differences in the biology and the clinical outcome between histiotypes. Genes involved in the mitotic checkpoint as a major mechanism of carcinogenesis in non-endometrioid endometrial cancer, or altered genes associated with the initial steps of myometrial infiltration in endometrioid endometrial cancer, represent examples of how useful large genetic screenings can be for understanding the tumorigenesis process and the future directions in the molecular pathogenesis of endometrial cancer.     

Human Ovarian Cancer Stroma Contains Luteinized Theca Cells Harboring Tumor Suppressor Gene GT198 Mutations

Ovarian cancer is a highly lethal gynecological cancer, and its causes remain to be understood. Using a recently identified tumor suppressor gene, GT198 (PSMC3IP), as a unique marker, we searched for the identity of GT198 mutant cells in ovarian cancer. GT198 has germ line mutations in familial and early onset breast and ovarian cancers and recurrent somatic mutations in sporadic fallopian tube cancers. GT198 protein has been shown as a steroid hormone receptor coregulator and also as a crucial factor in DNA repair. In this study, using GT198 as a marker for microdissection, we find that ovarian tumor stromal cells harboring GT198 mutations are present in various types of ovarian cancer including high and low grade serous, endometrioid, mucinous, clear cell, and granulosa cell carcinomas and in precursor lesions such as inclusion cysts. The mutant stromal cells consist of a luteinized theca cell lineage at various differentiation stages including CD133⁺, CD44⁺, and CD34⁺ cells, although the vast majority of them are differentiated overexpressing steroidogenic enzyme CYP17, a theca cell-specific marker. In addition, wild type GT198 suppresses whereas mutant GT198 protein stimulates CYP17 expression. The chromatin-bound GT198 on the human CYP17 promoter is decreased by overexpressing mutant GT198 protein, implicating the loss of wild type suppression in mutant cells. Together, our results suggest that GT198 mutant luteinized theca cells overexpressing CYP17 are common in ovarian cancer stroma. Because first hit cancer gene mutations would specifically mark cancer-inducing cells, the identification of mutant luteinized theca cells may add crucial evidence in understanding the cause of human ovarian cancer.