Ovulatory Follicular Fluid Facilitates the Full Transformation Process for the Development of High-Grade Serous Carcinoma

Ovulation sources ROS to confer mutagenic activities on the TP53 gene in the fallopian tube epithelium

INTRODUCTION

Epidemiological studies have implicated ovulation as a risk factor for ovarian high-grade serous carcinoma (HGSC) at the initiation stage. Precancerous lesions of HGSC commonly exhibit TP53 mutations attributed to DNA deamination and are frequently localized in the fallopian tube epithelium (FTE), a site regularly exposed to ovulatory follicular fluid (FF). This study aimed to assess the mutagenic potential of FF and investigate the expression levels and functional role of activation-induced cytidine deaminase (AID) following ovulation, along with the resulting TP53 DNA deamination.

METHODS

The mutagenic activity of FF toward premalignant and malignant FTE cells was determined using the hypoxanthine phosphoribosyl transferase (HPRT) mutation assay with or without AID knockdown. The sequential activation of AID, including expressional induction, nuclear localization, DNA binding, and deamination, was determined. AID inducers in FF were identified, and the times of action and signaling pathways were determined.

RESULTS

FF induced AID activation and de novo FTE cell mutagenesis in two waves of activity in accordance with post-ovulation FF exposure. The ERK-mediated early activity started at 2 min and peaked at 45 min, and the NF-κB-mediated late activity started at 6 h and peaked at 8.5 h after exposure. ROS, TNF-α, and estradiol, which are abundant in FF, all induced the two activities, while all activities were abolished by antioxidant cotreatment. AID physically bound to and biochemically deaminated the TP53 gene, regardless of known mutational hotspots. It did not act on other prevalent tumor-suppressor genes of HGSC.

CONCLUSION

This study revealed the ROS-dependent AID-mediated mutagenic activity of the ovulatory FF. The results filled up the missing link between ovulation and the initial TP53 mutation and invited a strategy of antioxidation in prevention of HGSC.

Epidermal growth factor receptor ligands enriched in follicular fluid exosomes promote oncogenesis of fallopian tube epithelial cells

BACKGROUND

Incessant ovulation is the main etiologic factor of ovarian high-grade serous carcinomas (HGSC), which mostly originate from the fallopian tube epithelium (FTE). Receptor tyrosine kinase (RTK) ligands essential for follicle development and ovulation wound repair were abundant in the follicular fluid (FF) and promoted the transformation of FTE cells. This study determined whether RTK ligands are present in FF exosomes and whether epidermal growth factor receptor (EGFR) signaling is essential for oncogenic activity.

METHODS

The FF of women undergoing in vitro fertilization was fractionated based on the richness of exosomes and tested for transformation toward FTE cells under different RTK inhibitors. EGFR ligands in FF exosomes were identified, and downstream signaling proteins in FTE cells were characterized.

RESULTS

The transforming activity of FF was almost exclusively enriched in exosomes, which possess a high capacity to induce anchorage-independent growth, clonogenicity, migration, invasion, and proliferation of FTE cells. EGFR inhibition abolished most of these activities. FF and FF exosome exposure markedly increased EGFR phosphorylation and the downstream signal proteins, including AKT, MAPK, and FAK. Multiple EGF family growth factors, such as amphiregulin, epiregulin, betacellulin, and transforming growth factor-alpha, were identified in FF exosomes.

CONCLUSIONS

Our results demonstrate that FF exosomes serve as carriers of EGFR ligands as well as ligands of other RTKs that mediate the transformation of FTE cells and underscore the need to further explore the content and roles of FF exosomes in HGSC development.

Human peritoneal fluid exerts ovulation- and nonovulation-sourced oncogenic activities on transforming fallopian tube epithelial cells

Secretory cells in the fallopian tube fimbria epithelium (FTE) are regarded as the main cells of origin of ovarian high-grade serous carcinoma (HGSC). Ovulation is the main cause of FTE oncogenesis, which proceeds through a sequence of TP53 mutations, chromosomal instability due to Rb/cyclin E aberration, in situ carcinoma (STIC), and metastasis to the ovary and peritoneum (metastatic HGSC). Previously, we have identified multiple oncogenic activities of the ovulatory follicular fluid (FF), which exerts the full spectrum of transforming activity on FTE cells at different stages of transformation. After ovulation, the FF is transfused into the peritoneal fluid (PF), in which the FTE constantly bathes. We wondered whether PF exerts the same spectrum of oncogenic activities as done by FF and whether these activities are derived from FF. By using a panel of FTE cell lines with p53 mutation (FT282-V), p53/CCNE1 aberrations (FT282-CCNE1), and p53/Rb aberrations plus spontaneous transformation, and peritoneal metastasis (FEXT2), we analyzed the changes of different transformation phenotypes after treating with FF and PF collected before or after ovulation. Similar to effects exhibited by FF, we found that, to a lesser extent, PF promoted anchorage-independent growth (AIG), migration, anoikis resistance, and peritoneal attachment in transforming FTE cells. The more transformed cells were typically more affected. Among the transforming activities exhibited by PF treatment, AIG, Matrigel invasion, and peritoneal attachment growth were higher with luteal-phase PF treatment than with the proliferative-phase PF treatment, suggesting an ovulation source. In contrast, changes in anoikis resistance and migration activities were similar in response to treatment with PF collected before and after ovulation, suggesting an ovulation-independent source. The overall transforming activity of luteal-phase PF was verified in an i.p. co-injection xenograft mouse model. Co-injection of Luc-FEXT2 cells with either FF or luteal-phase PF supported early peritoneal implantation, whereas co-injection with follicular-phase PF did not. This study, for the first time, demonstrates that PF from ovulating women can promote different oncogenic phenotypes in FTE cells at different stages of malignant transformation. Most of these activities, other than anoikis resistance and cell migration, are sourced from ovulation.

Ovulation provides excessive coagulation and hepatocyte growth factor signals to cause postoperative intraabdominal adhesions

Postoperative adhesions show a higher occurrence in females aged 16-60, especially after pelvic surgeries. This study explores the role of ovulation in adhesion formation in mice. Ovarian surgery in mice with normal- or super-ovulation led to pronounced adhesions, whereas ovulation-defective Pgr-KO mice showed minimal adhesions. Specifically, exposure to ovulatory follicular fluid (FF) markedly increased the adhesion. The hazardous exposure time window was one day before to 2.5 days after the surgery. Mechanistically, early FF exposure triggered adhesions via the blood coagulation cascade, while later exposure relied on the HGF/cMET signaling pathway. Prophylactic administration of a thrombin inhibitor pre-operatively or a cMET inhibitor postoperatively effectively mitigated FF-induced adhesions, while COX inhibitor treatment exhibited no discernible effect. These findings underscore ovulation as a pivotal factor in the development of pelvic wound adhesions and advocate for targeted preventive strategies such as c-MET inhibition, scheduling surgeries outside the ovulatory period, or employing oral contraceptive measures.

Follicular fluid aids cell adhesion, spreading in an age independent manner and shows an age-dependent effect on DNA damage in fallopian tube epithelial cells

Ovarian cancer (OC) is deadly, and likely arises from the fallopian tube epithelium (FTE). Despite the association of OC with ovulation, OC typically presents in post-menopausal women who are no longer ovulating. The goal of this study was to understand how ovulation and aging interact to impact OC progression from the FTE. Follicular fluid released during ovulation induces DNA damage in the FTE, however, the role of aging on FTE exposure to follicular fluid is unexplored. Follicular fluid samples were collected from 14 women and its effects on FTE cells was assessed. Follicular fluid caused DNA damage and lipid oxidation in an age-dependent manner, but instead induced cell proliferation in a dose-dependent manner, independent of age in FTE cells. Follicular fluid regardless of age disrupted FTE spheroid formation and stimulated attachment and growth on ultra-low attachment plates. Proteomics analysis of the adhesion proteins in the follicular fluid samples identified vitronectin, a glycoprotein responsible for FTE cell attachment and spreading.

Reevaluating the Role of Progesterone in Ovarian Cancer: Is Progesterone Always Protective?

Ovarian cancer (OC) represents a collection of rare but lethal gynecologic cancers where the difficulty of early detection due to an often-subtle range of abdominal symptoms contributes to high fatality rates. With the exception of BRCA1/2 mutation carriers, OC most often manifests as a post-menopausal disease, a time in which the ovaries regress and circulating reproductive hormones diminish. Progesterone is thought to be a "protective" hormone that counters the proliferative actions of estrogen, as can be observed in the uterus or breast. Like other steroid hormone receptor family members, the transcriptional activity of the nuclear progesterone receptor (nPR) may be ligand dependent or independent and is fully integrated with other ubiquitous cell signaling pathways often altered in cancers. Emerging evidence in OC models challenges the singular protective role of progesterone/nPR. Herein, we integrate the historical perspective of progesterone on OC development and progression with exciting new research findings and critical interpretations to help paint a broader picture of the role of progesterone and nPR signaling in OC. We hope to alleviate some of the controversy around the role of progesterone and give insight into the importance of nPR actions in disease progression. A new perspective on the role of progesterone and nPR signaling integration will raise awareness to the complexity of nPRs and nPR-driven gene regulation in OC, help to reveal novel biomarkers, and lend critical knowledge for the development of better therapeutic strategies.

Insulin-like growth factor (IGF) and hepatocyte growth factor (HGF) in follicular fluid cooperatively promote the oncogenesis of high-grade serous carcinoma from fallopian tube epithelial cells: Dissection of the molecular effects

Incessant ovulation is believed to be a potential cause of epithelial ovarian cancer (EOC). Our previous investigations have shown that insulin-like growth factor (IGF2) and hepatocyte growth factor (HGF) in the ovulatory follicular fluid (FF) contributed to the malignant transformation initiated by p53 mutations. Here we examined the individual and synergistic impacts of IGF2 and HGF on enhancing the malignant properties of high-grade serous carcinoma (HGSC), the most aggressive type of EOC, and its precursor lesion, serous tubal intraepithelial carcinoma (STIC). In a mouse xenograft co-injection model, we observed that FF co-injection induced tumorigenesis of STIC-mimicking cells, FE25. Co-injection with IGF2 or HGF partially recapitulated the tumorigenic effects of FF, but co-injection with both resulted in a higher tumorigenic rate than FF. We analyzed the different transformation phenotypes influenced by these FF growth signals through receptor inhibition. The IGF signal was necessary for clonogenicity, while the HGF signal played a crucial role in the migration and invasion of STIC and HGSC cells. Both signals were necessary for the malignant phenotype of anchoring-independent growth but had little impact on cell proliferation. The downstream signals responsible for these HGF activities were identified as the tyrosine-protein kinase Met (cMET)/mitogen-activated protein kinase and cMET/AKT pathways. Together with the previous finding that the FF-IGF2 could mediate clonogenicity and stemness activities via the IGF-1R/AKT/mammalian target of rapamycin and IGF-1R/AKT/NANOG pathways, respectively, this study demonstrated the cooperation of the FF-sourced IGF and HGF growth signals in the malignant transformation and progression of HGSC through both common and distinct signaling pathways. These findings help develop targeted prevention of HGSC.

Lifetime ovulatory years and risk of epithelial ovarian cancer: a multinational pooled analysis

BACKGROUND

The role of ovulation in epithelial ovarian cancer (EOC) is supported by the consistent protective effects of parity and oral contraceptive use. Whether these factors protect through anovulation alone remains unclear. We explored the association between lifetime ovulatory years (LOY) and EOC.

METHODS

LOY was calculated using 12 algorithms. Odds ratios (ORs) and 95% confidence intervals (CIs) estimated the association between LOY or LOY components and EOC among 26 204 control participants and 21 267 case patients from 25 studies. To assess whether LOY components act through ovulation suppression alone, we compared beta coefficients obtained from regression models with expected estimates assuming 1 year of ovulation suppression has the same effect regardless of source.

RESULTS

LOY was associated with increased EOC risk (OR per year increase = 1.014, 95% CI = 1.009 to 1.020 to OR per year increase = 1.044, 95% CI = 1.041 to 1.048). Individual LOY components, except age at menarche, also associated with EOC. The estimated model coefficient for oral contraceptive use and pregnancies were 4.45 times and 12- to 15-fold greater than expected, respectively. LOY was associated with high-grade serous, low-grade serous, endometrioid, and clear cell histotypes (ORs per year increase = 1.054, 1.040, 1.065, and 1.098, respectively) but not mucinous tumors. Estimated coefficients of LOY components were close to expected estimates for high-grade serous but larger than expected for low-grade serous, endometrioid, and clear cell histotypes.

CONCLUSIONS

LOY is positively associated with nonmucinous EOC. Differences between estimated and expected model coefficients for LOY components suggest factors beyond ovulation underlie the associations between LOY components and EOC in general and for non-HGSOC.

CCNE1 is a potential target of Metformin for tumor suppression of ovarian high-grade serous carcinoma

High-grade serous ovarian cancer (HGSOC) is the most common and malignant type of ovarian cancer, accounting for 70%-80% of mortality. However, the treatment of HGSOC has improved little in the past few decades. Metformin is the first-line medication for the treatment of type 2 diabetes and has now gained more attention in cancer treatment. In this study, we sought to identify potential hub genes that metformin could target in the treatment of HGSOC. We downloaded GSE69428 and GSE69429 in the Gene Expression Omnibus database and performed the bioinformatics analysis. Subsequently, we analyzed the effect of Metformin in HGSOC through biological experiments. Molecular simulation docking was used to predict the interaction of Metformin and CCNE1. We chose CCNE1 for the study based on bioinformatics analysis, literature studies, and preliminary data. We evaluated that CCNE1 is overexpressed in HGSOC tissues and found that HGSOC cells with high CCNE1 expression increase sensitivity to Metformin treatment in the analysis of cell proliferation and anchorage-independent growth. Metformin could inhibit the expression of CCNE1, which is associated with the anti-proliferative effect of tumor cells. Moreover, Metformin could ameliorate the tumor growth in syngeneic orthotopic transplantation mouse models and xenograft tumorigenesis models. Furthermore, molecular simulation docking showed that Metformin may bind to CCNE1 protein, suggesting that CCNE1 could be a potential target for Metformin. Our data revealed that Metformin has antitumor effects on ovarian cancer and CCNE1 could be a potential target for Metformin.

Spontaneous Transformation of a p53 and Rb-Defective Human Fallopian Tube Epithelial Cell Line after Long Passage with Features of High-Grade Serous Carcinoma

Ovarian cancer is one of the most lethal gynecological cancers, and 80% are high-grade serous carcinomas (HGSOC). Despite advances in chemotherapy and the development of targeted therapies, the survival rate of HGSOC has only moderately improved. Therefore, a cell model that reflects the pathogenesis and clinical characteristics of this disease is urgently needed. We previously developed a human fallopian tube epithelial cell line (FE25) with p53 and Rb deficiencies. After long-term culture in vitro, cells at high-passage numbers showed spontaneous transformation (FE25L). This study aimed to compare FE25 cells cultured in vitro for low (passage 16-31) and high passages (passage 116-139) to determine whether these cells can serve as an ideal cell model of HGSOC. Compared to the cells at low passage, FE25L cells showed increased cell proliferation, clonogenicity, polyploidy, aneuploidy, cell migration, and invasion. They also showed more resistance to chemotherapy and the ability to grow tumors in xenografts. RNA-seq data also showed upregulation of hypoxia, epithelial-mesenchymal transition (EMT), and the NF-κB pathway in FE25L compared to FE25 cells. qRT-PCR confirmed the upregulation of EMT, cytokines, NF-κB, c-Myc, and the Wnt/β-catenin pathway. Cross-platform comparability found that FE25L cells could be grouped with the other most likely HGSOC lines, such as TYKNU and COV362. In conclusion, FE25L cells showed more aggressive malignant behavior than FE25 cells and hence might serve as a more suitable model for HGSOC research.

Versican secreted by the ovary links ovulation and migration in fallopian tube derived serous cancer

High grade serous ovarian cancers (HGSOC) predominantly arise in the fallopian tube epithelium (FTE) and colonize the ovary first, before further metastasis to the peritoneum. Ovarian cancer risk is directly related to the number of ovulations, suggesting that the ovary may secrete specific factors that act as chemoattractants for fallopian tube derived tumor cells during ovulation. We found that 3D ovarian organ culture produced a secreted factor that enhanced the migration of FTE non-tumorigenic cells as well as cells harboring specific pathway modifications commonly found in high grade serous cancers. Through size fractionation and a small molecule inhibitors screen, the secreted protein was determined to be 50-100kDa in size and acted through the Epidermal Growth Factor Receptor (EGFR). To correlate the candidates with ovulation, the PREDICT organ-on-chip system was optimized to support ovulation in a perfused microfluidic platform. Versican was found in the correct molecular weight range, contained EGF-like domains, and correlated with ovulation in the PREDICT system. Exogenous versican increased migration, invasion, and enhanced adhesion of both murine and human FTE cells to the ovary in an EGFR-dependent manner. The identification of a protein secreted during ovulation that impacts the ability of FTE cells to colonize the ovary provides new insights into the development of strategies for limiting primary ovarian metastasis.

Effect of ovulation IGF and HGF signaling on the oncogenesis of murine epithelial ovarian cancer cell ID8

The incidence and mortality of epithelial ovarian cancer (EOC) are increasing in Taiwan and worldwide. The prognosis of this disease has improved little in the last few decades due to insufficient knowledge of the etiology. Previous studies on the role of ovulation in the development of EOC have unveiled IGF2, HGF, and other carcinogens in ovulatory follicular fluid (FF) that exert transformation activities on the exposed fallopian tube fimbria epithelium. However, an orthotopic proof in an animal model is lacking. By using the murine ID8 EOC cells and the syngenic transplantation model, this study explored the effect of FF on the oncogenesis of mouse ovarian cancer. We found FF promoted clonogenicity and anchorage-independent growth of ID8 cells, largely through the IGF-1R and cMET signaling. In contrast, FF modestly promoted cell proliferation independent of the two signals and did not affect cell migration and invasion. Transplantation of ID8 cells into the ovarian bursa of C57BL6/J mice orthotopically grew ovarian tumors and metastasized to the peritoneum with ascites formation. The tumorigenic rate and severity of the disease were positively correlated with the level of IGF-1R and cMET receptors on the cell surface. Our data demonstrated that ovulation, through the signaling of IGF/IGF-1R and HGF/cMET, promotes oncogenic phenotypes in a murine EOC model. The results provide further proof of the carcinogenic effect of ovulation in the development of EOC.

The Double Engines and Single Checkpoint Theory of Endometriosis

Endometriosis is a chronic disease characterized by the ectopic localization of the endometrial tissue in the peritoneal cavity. Consequently, it causes local pathological changes and systemic symptoms, affecting at least one in every ten women. This disease is difficult to diagnose early, it is prone to dissemination, is difficult to eradicate, tends to recur, and is regarded as “a cancer of no kill”. Indeed, the development of endometriosis closely resembles that of cancer in the way of mutagenesis, pelvic spreading, and immunological adaptation. While retrograde menstruation has been regarded as the primary cause of endometriosis, the role of ovulation and menstrual stimuli in the development of endometriosis has long been overlooked. The development of ovarian and peritoneal endometrioses, similar to the development of high-grade serous carcinoma in the fallopian tube fimbriae with intraperitoneal metastasis, depends highly on the carcinogens released during ovulation. Moreover, endometriosis carries an extremely hypermutated genome, which is non-inferior to the ultra-mutated endometrial cancer. The hypermutation would lead to an overproduction of new proteins or neoantigens. Because of this, the developing endometriosis may have to turn on the PD-1/PDL-1 “self-tolerance” checkpoint to evade immune surveillance, leaving an Achilles tendon for an immune checkpoint blockade. In this review, we present the double engines and single checkpoint theory of the genesis of endometriosis, provide the current pieces of evidence supporting the hypothesis, and discuss the new directions of prevention and treatment.

Ovulation Enhances Intraperitoneal and Ovarian Seedings of High-Grade Serous Carcinoma Cells Originating from the Fallopian Tube: Confirmation in a Bursa-Free Mouse Xenograft Model

Background: Recently, new paradigms for the etiology and origin of ovarian high-grade serous carcinoma (HGSC) have emerged. The carcinogens released during ovulation transform fallopian tube epithelial cells, exfoliating and metastasizing to the peritoneal organs, including the ovaries. Solid in vivo evidence of the paradigms in a mouse model is urgently needed but is hampered by the differing tubo-ovarian structures. In mice, there is a bursa structure surrounding the distal oviduct and ovary. This, on one hand, prevents the direct influence of ovulatory follicular fluid (FF) on the exfoliated tumor cells. On the other hand, it hinders the seeding of exfoliated tumor cells into the ovary. Methods: In this study, we created a bursa-free mouse xenograft model to examine the effect of superovulation on peritoneal and ovarian metastases of transformed human tubal epithelial cells after intraperitoneal injection in NSG mice. Results: The bursa-free mouse model showed a better effect of ovulation on peritoneal metastasis. In this model, superovulation increased the number of transformed human tubal epithelial cell seedlings after intraperitoneal injection. Compared to the bursa-intact state, bursa-free ovaries were more vulnerable to external tumor seeding in either normal ovulation or superovulation state. Conclusions: This study provides the first in vivo evidence that intraperitoneal spreading of tubal HGSC cells is enhanced by ovulation. This study also demonstrated a mouse model for studying ovary-peritoneum interaction in cancer development.

Models for measuring metabolic chemical changes in the metastasis of high grade serous ovarian cancer: fallopian tube, ovary, and omentum

Ovarian cancer (OC) is the most lethal gynecologic malignancy and high grade serous ovarian cancer (HGSOC) is the most common and deadly subtype, accounting for 70-80% of OC deaths. HGSOC has a distinct pattern of metastasis as many believe it originates in the fallopian tube and then it metastasizes first to the ovary, and later to the adipose-rich omentum. Metabolomics has been heavily utilized to investigate metabolite changes in HGSOC tumors and metastasis. Generally, metabolomics studies have traditionally been applied to biospecimens from patients or animal models; a number of recent studies have combined metabolomics with innovative cell-culture techniques to model the HGSOC metastatic microenvironment for the investigation of cell-to-cell communication. The purpose of this review is to serve as a tool for researchers aiming to model the metastasis of HGSOC for metabolomics analyses. It will provide a comprehensive overview of current knowledge on the origin and pattern of metastasis of HGSOC and discuss the advantages and limitations of different model systems to help investigators choose the best model for their research goals, with a special emphasis on compatibility with different metabolomics modalities. It will also examine what is presently known about the role of small molecules in the origin and metastasis of HGSOC.

Ovulation sources coagulation protease cascade and hepatocyte growth factor to support physiological growth and malignant transformation

•

Ovulatory follicular fluid exerts a long-lasting transformation activity covering throughout the ovulation cycle.

•

The ovulation injury-coagulation proteases-hepatocyte growth factor (HGF) cascade is responsible for the sustained activity.

•

Ovulation sources HGF into the peritoneal cavity, then into the blood circulation.

•

This coagulation-HGF cascade promotes the transformation of fallopian tube epithelial cells and ovarian cancer cells.

•

Physiologically, it promotes the growth of the corpus luteum and injured epithelium after ovulation.

The fallopian tube fimbrial epithelium, which is exposed to the follicular fluid (FF) contents of ovulation, is regarded as the main origin of ovarian high-grade serous carcinoma. Previously, we found that growth factors in FF, such as IGF2, are responsible for the malignant transformation of fallopian tube epithelium. However, ovulation is a monthly transient event, whereas carcinogenesis requires continuous, long-term exposure. Here, we found the transformation activity of FF sustained for more than 30 days after drainage into the peritoneal fluid (PF). Hepatocyte growth factor (HGF), activated through the ovulation injury-tissue factor–thrombin–HGF activator (HGFA)–HGF cleavage cascade confers a sustained transformation activity to fallopian tube epithelium, high-grade serous carcinoma. Physiologically, the high reserve of the coagulation-HGF cascade sources a sustained level of HGF in PF, then to the blood circulation. This HGF axis promotes the growth of the corpus luteum and repair of tissue injury after ovulation.

Cellular models of development of ovarian high-grade serous carcinoma: A review of cell of origin and mechanisms of carcinogenesis

High-grade serous carcinoma (HGSC) is the most common and malignant histological type of epithelial ovarian cancer, the origin of which remains controversial. Currently, the secretory epithelial cells of the fallopian tube are regarded as the main origin and the ovarian surface epithelial cells as a minor origin. In tubal epithelium, these cells acquire TP53 mutations and expand to a morphologically normal 'p53 signature' lesion, transform to serous tubal intraepithelial carcinoma and metastasize to the ovaries and peritoneum where they develop into HGSC. This shifting paradigm of the main cell of origin has revolutionarily changed the focus of HGSC research. Various cell lines have been derived from the two cellular origins by acquiring immortalization via overexpression of hTERT plus disruption of TP53 and the CDK4/RB pathway. Malignant transformation was achieved by adding canonical driver mutations (such as gain of CCNE1) revealed by The Cancer Genome Atlas or by noncanonical gain of YAP and miR181a. Alternatively, because of the extreme chromosomal instability, spontaneous transformation can be achieved by long passage of murine immortalized cells, whereas in humans, it requires ovulatory follicular fluid, containing regenerating growth factors to facilitate spontaneous transformation. These artificially and spontaneously transformed cell systems in both humans and mice have been widely used to discover carcinogens, oncogenic pathways and malignant behaviours in the development of HGSC. Here, we review the origin, aetiology and carcinogenic mechanism of HGSC and comprehensively summarize the cell models used to study this fatal cancer having multiple cells of origin and overt genomic instability.