Aetiological importance of ovulation in epithelial ovarian cancer: a population based study

A Review of Principal Studies on the Development and Treatment of Epithelial Ovarian Cancer in the Laying Hen Gallus gallus

Often referred to as the silent killer, ovarian cancer is the most lethal gynecologic malignancy. This disease rarely shows any physical symptoms until late stages and no known biomarkers are available for early detection. Because ovarian cancer is rarely detected early, the physiology behind the initiation, progression, treatment, and prevention of this disease remains largely unclear. Over the past 2 decades, the laying hen has emerged as a model that naturally develops epithelial ovarian cancer that is both pathologically and histologically similar to that of the human form of the disease. Different molecular signatures found in human ovarian cancer have also been identified in chicken ovarian cancer including increased CA125 and elevated E-cadherin expression, among others. Chemoprevention studies conducted in this model have shown that decreased ovulation and inflammation are associated with decreased incidence of ovarian cancer development. The purpose of this article is to review the major studies performed in laying hen model of ovarian cancer and discuss how these studies shape our current understanding of the pathophysiology, prevention, and treatment of epithelial ovarian cancer.

Physiological changes associated with the menstrual cycle: a review

The cyclic hormonal changes that regulate the menstrual cycle are a significant biological influence on the female body, one with both physical and emotional ramifications. Menstruation is governed by tightly orchestrated changes in the levels of ovarian estrogen and progesterone, which produce varying responses in diverse tissues and organs. The skin, the largest organ in the body, is replete with estrogen receptors (in both dermis and epidermis) and to a lesser extent, progesterone receptors. Cyclically fluctuating levels of estrogen and progesterone influence numerous characteristics of the epidermis, including skin surface lipid secretion and sebum production, skin thickness, fat deposition, skin hydration, and barrier function. Dermal collagen content, which contributes to skin elasticity and resistance to wrinkling, is also influenced. Interestingly, estrogen levels also influence skin pigmentation and UV susceptibility, as well as resident microflora. In addition, changing hormone levels across the menstrual cycle produce measurable variations in immune function and disease susceptibility. An understanding of the profound influence that fluctuating estrogen and progesterone levels have on the biological responses of the premenopausal adult woman is critical to optimizing the efficacy of medical therapies in this population.

Cultures of ovarian surface epithelium from women with and without a hereditary predisposition to develop female adnexal carcinoma

AIM

Conflicting evidence exists on whether in vivo morphological characteristics can distinguish Ovarian Surface Epithelium (OSE) of ovaries obtained from women with and without a predisposition to develop female adnexal (ovarian and fallopian tube) carcinoma. This study aims to detect differences in growth potential and morphology that are maintained or specifically expressed in vitro.

STUDY DESIGN

Ovarian surfaces were scraped to retrieve OSE cells from 56 women at hereditary high risk for female adnexal carcinoma, of whom 33 are BRCA1 and four are BRCA2 mutation carriers (Predisposed OSE, POSE) and from 26 women without such risk (Non Predisposed OSE, NPOSE). Number of passages and total cell yield until last passage, as well as morphology was compared between both groups. To confirm morphology, the expression of epithelial, mesothelial, and fibroblast markers was assessed.

RESULTS

Both POSE and NPOSE cultures displayed similar growth potential and morphology. The expression of epithelial markers cyto-keratins 7 and 8 was similar between both groups. Only in cultures in which cells did not uniformly exhibit these markers, the percentage of cells expressing these markers was significantly lower at last passage when compared to the initial culture. In these latter cultures, cells that were morphologically indistinguishable from fibroblasts were observed. Mesothelial marker calretinin was expressed in 75% of cells of both POSE and NPOSE cultures and correlates with cyto-keratins 7 and 8 expression. CA 125 expression was equally low in POSE and NPOSE cultures (4.3%). Fibroblast markers FSM and vimentin were expressed in 100% and collagen IV was expressed in 16% of cells in all cultures.

CONCLUSION

OSE cells derived from women with a hereditary predisposition to develop female adnexal cancer possess similar in vitro characteristics as OSE from women without this predisposition. On basis of our results, it seems advisable to study only 100% cyto-keratins 7 and 8 positive OSE cultures, since contamination of fibroblasts in some primary OSE cultures cannot be ruled out.

Hormonal etiology of epithelial ovarian cancer, with a hypothesis concerning the role of androgens and progesterone

In the United States, ovarian cancer is the fourth most frequent cause of cancer death among women, following lung, breast, and colorectal cancers. Each year, approximately 26,000 women are diagnosed with ovarian cancer and 14,000 die of it. Germline mutations in BRCA1, BRCA2, or other genes have been implicated in a small fraction of cases. However, it has been suggested that, for the great majority of patients, the risk of epithelial ovarian cancer could be related to "incessant ovulation" (i.e., to the chronically repeated formation of stromal epithelial clefts and inclusion cysts following ovulation) or to some type of hormonal stimulation of ovarian epithelial cells, either on the surface of the ovary or within ovarian inclusion cysts, possibly mediated through excessive gonadotropin secretion. From the evidence to date, the relative importance of these two hypotheses--incessant ovulation and gonadotropin stimulation--cannot be distinguished. While either or both may play a role in the development of ovarian cancer, it appears that an additional major factor must also be involved. The purpose of this review is to evaluate evidence for and against the incessant ovulation and gonadotropin hypotheses, as well as to consider the possibility that risk of ovarian cancer may be increased by factors associated with excess androgenic stimulation of ovarian epithelial cells and may be decreased by factors related to greater progesterone stimulation. Many features of the evidence bearing on the pathophysiology of ovarian cancer appear to support a connection with androgens and progesterone.

Is cystic ovarian endometriosis an asymmetric disease?

OBJECTIVE

To investigate whether asymmetry exists in the left- and right-handed distribution of ovarian cystic lesions in a large series of women with endometriosis.

DESIGN

Retrospective evaluation of a case series.

SETTING

Tertiary care and referral academic centre for the study and treatment of endometriosis.

POPULATION

A total of 1054 consecutive women undergoing first-line surgical treatment for endometriosis in an eight-year period.

METHODS

Data were collected on indication for the intervention, age at surgery, parity and disease stage as well as side and size of ovarian endometriomas.

MAIN OUTCOME MEASURE

Frequency of left- and right-sided ovarian endometriomas.

RESULTS

Histologically confirmed endometriotic ovarian cysts were present in 561 women, which were on the left side in 255 instances, on the right in 148, and bilateral in 158. In the patients with unilateral endometriomas, the observed proportion of left cysts (255/403, 63%; 95% confidence interval, 58% to 68%) was significantly different from the expected proportion of 50%, (chi2(1), 28.41, P<0.001). Including also the bilateral endometriotic cysts gave a total of 413/719 (57%) left-sided and 306/719 right-sided endometriomas. The magnitude of these proportions did not vary appreciably during the eight years considered. The difference in proportion of left- and right-sided endometriotic cysts was virtually similar in subgroups of women with different indications for surgery. Cyst side was not related to age, parity or cyst diameter.

CONCLUSIONS

The finding of a lateral asymmetry in the occurrence of ovarian endometriotic cysts is compatible with the anatomical differences of the left and right hemipelvis and supports the menstrual reflux theory.

Ovarian cancer, ovulation and side of origin

Reports of more right-sided ovarian cancers and more ovulations in the right ovary seemed to offer powerful support for the theory that ovulation, per se, leads to ovarian cancer risk. We examined laterality in 25,692 epithelial ovarian cancers diagnosed in 1973-89 included in the US Surveillance, Epidemiology, and End Results system of cancer registries. Ovarian cancer occurred equally often in the left and right ovaries in this large series of incident cases.

Epidemiology, etiology, and fertility drugs in ovarian epithelial carcinoma: where are we today?

OBJECTIVE

To review studies that have examined the epidemiology and etiology of the development of epithelial carcinoma of the ovary.

DATA IDENTIFICATION

Important published studies related to the topic were identified through a computerized bibliography search.

CONCLUSION

A review of the literature reveals that the etiology of epithelial ovarian cancer is probably multifactorial and that genetic, environmental, hormonal, and viral factors appear to be directly or indirectly related to the development of the disease. An attempt to implicate specific agents has not produced conclusive results. However, based on large epidemiologic studies, it seems that there is a clear trend of decreasing risk with increasing number of pregnancies, deliveries, use of oral contraceptives, and the duration of breast feeding. An increased risk was found to be associated with ovarian dysfunction leading to infertility and exposure to asbestos and talc. The recent observation that infertile women who used fertility drugs might experience an increased risk for the development of epithelial ovarian cancer should be examined very carefully because of the small number of patients in the study, lack of appropriate information about the type of infertility, drugs used, dosage, and duration of treatment. Because there are no screening tests that are consistently accurate enough to detect ovarian cancer at an early stage, translating the current information into disease prevention requires careful clinical evaluation with a routine follow-up of patients at risk.

Ovulation side and ovarian cancer

Previous reports have suggested a predilection for right-sided ovulation and that epithelial ovarian cancer arises more commonly in the right ovary, thus establishing a possible causal relationship between ovulation and ovarian cancer. However, evaluation of ovulation patterns in consecutive cycles has produced contradictory results and there are no reports corroborating a higher incidence of right-sided ovarian cancers. We reviewed the records of 293 patients with epithelial ovarian cancer and found no significant difference between the frequency of tumors in the right and left ovaries. We also prospectively analyzed the side of ovulation in 41 unselected consecutive patients undergoing 156 in vitro fertilization cycles without ovarian stimulation. Follicular development was carefully monitored by daily ultrasonic scan and estradiol and LH plasma determinations. Eight-two ovulations (52%) were on the right (not statistically significant). Thus our results bring into question previous studies suggesting a link between the side of ovulation and epithelial ovarian cancer.