A prospective cohort study of oral contraceptive use and ovarian cancer among women in the United States born from 1947 to 1964

Assessing the impact of contraceptive use on reproductive cancer risk among women of reproductive age-a systematic review

Background

Contraceptives play a crucial role in women's reproductive health, their hormonal components may be linked to cancer risks, specifically breast, and gynecological cancers. Given the high usage rates of hormonal contraceptives, it is vital to systematically evaluate their potential impact on cancer outcomes, especially among women with a family history of gynecological cancers.

Objectives

This study aims to evaluate the evidence on the association between modern contraceptive use and the risk of breast and reproductive cancers (ovarian, endometrial, and cervical cancer) among women of reproductive age, to inform healthcare providers, women, and program managers about cancer outcomes related to contraceptive use.

Methods

A systematic review was conducted according to PRISMA guidelines. Searches were performed in databases such as CINAHL, OVID Medline, EMBASE, and more from inception to February 2022. Eligible studies included randomized controlled trials, cohort studies, and case-control studies that compared cancer outcomes between contraceptive users and non-users. Data extraction, quality assessment, and meta-analyses were conducted following predefined protocols. Subgroup and sensitivity analyses examined variations in contraceptive methods, doses, and duration.

Results

A total of 51 studies were included, comprising 2 RCTs and 49 observational studies. The review identified a significant reduction in ovarian and endometrial cancer incidence among contraceptive users. Hormonal contraceptive users had a 36% lower risk of ovarian cancer (RR 0.64, 95% CI 0.60-0.68), with specific reductions seen in combined oral contraceptive users (RR 0.62, 95% CI 0.57-0.68) and hormonal IUD users (RR 0.68, 95% CI 0.48-0.96). The rate ratio of cervical cancer was higher among non- users compared to hormonal contraceptive users when we pooled the results (1.28, 95% CI 1.21, 1.35). No significant association was found between contraceptive use and breast cancer risk among healthy women (RR 1.00, 95% CI 0.94-1.06). However, BRCA1/2 mutation carriers using oral contraceptives showed a heightened risk of breast cancer (HR 1.39, 95% CI 1.15-1.67).

Conclusion

This systematic review highlights the protective effects of modern contraceptives against ovarian and endometrial cancers while identifying an increased risk of cervical. No significant breast cancer risk was found for healthy women, but BRCA1/2 mutation carriers faced increased risks. These findings underscore the need for personalized contraceptive counselling that considers cancer risk factors. Further research is needed to explore contraceptive impacts across different genetic profiles and dosing regimens.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, Prospero (CRD42022332647).

The association between oral contraceptive pills and ovarian cancer risk: A systematic review and meta-analysis

INTRODUCTION

Previous study results have been inconclusive, so this meta-analysis aims to evaluate the association between ovarian cancer and oral contraceptive pills (OCPs).

METHODS

PubMed, EMBASE, Scopus, and Web of Science were searched to identify studies on the association between OCPs and ovarian cancer from January 1, 2000 through February 5, 2023. The pooled relative risk (RR) and odds ratio (OR) were used to measure this relationship.

RESULTS

A total of 67 studies were included. In the association between ever-use compared with never-use of OCPs and ovarian cancer risk, the pooled RR in cohort studies was 0.69 [95% CI: 0.61, 0.78]. For the relationship between duration of OCPs use and ovarian cancer in the cohort studies, no association between duration of use1-12 months 0.92 [95% CI: 0.82, 1.03] and duration of use 13-60 months 0.87 [95% CI: 0.73, 1.04], but there is a statistically significant inverse relationship between duration of use 61-120 months 0.62 [95% CI: 0.48, 0.81] and more than 120 months 0.51 [95% CI: 0.32, 0.80] and ovarian cancer. For the relationship between OCPs and histological subtype of epithelial ovarian cancer in the cohort studies, the pooled RR for invasive was 0.70 [95% CI: 0.56, 0.87], but no association between OCPs and borderline ovarian cancer 0.64 [95% CI: 0.31, 1.31].

CONCLUSION

Our analysis shows a statistically significant inverse relationship between ever-use compared to never-use of OCPs and ovarian cancer risk,and also between invasive cancer and OCPs. By increasing the duration of OCPs use, the risk of ovarian cancer decreased.

Global epidemiology of epithelial ovarian cancer

Globally, ovarian cancer is the eighth most common cancer in women, accounting for an estimated 3.7% of cases and 4.7% of cancer deaths in 2020. Until the early 2000s, age-standardized incidence was highest in northern Europe and North America, but this trend has changed; incidence is now declining in these regions and increasing in parts of eastern Europe and Asia. Ovarian cancer is a very heterogeneous disease and, even among the most common type, namely epithelial ovarian cancer, five major clinically and genetically distinct histotypes exist. Most high-grade serous ovarian carcinomas are now recognized to originate in the fimbrial ends of the fallopian tube. This knowledge has led to more cancers being coded as fallopian tube in origin, which probably explains some of the apparent declines in ovarian cancer incidence, particularly in high-income countries; however, it also suggests that opportunistic salpingectomy offers an important opportunity for prevention. The five histotypes share several reproductive and hormonal risk factors, although differences also exist. In this Review, we summarize the epidemiology of this complex disease, comparing the different histotypes, and consider the potential for prevention. We also discuss how changes in the prevalence of risk and protective factors might have contributed to the observed changes in incidence and what this might mean for incidence in the future.

Perfluorooctanoic Acid (PFOA) Exposure Compromises Fertility by Affecting Ovarian and Oocyte Development

PFOA, a newly emerging persistent organic pollutant, is widely present in various environmental media. Previous reports have proved that PFOA exposure can accumulate in the ovary and lead to reproductive toxicity in pregnant mice. However, the potential mechanism of PFOA exposure on fertility remains unclear. In this study, we explore how PFOA compromises fertility in the zebrafish. The data show that PFOA (100 mg/L for 15 days) exposure significantly impaired fertilization and hatching capability. Based on tissue sections, we found that PFOA exposure led to ovarian damage and a decrease in the percentage of mature oocytes. Moreover, through in vitro incubation, we determined that PFOA inhibits oocyte development. We also sequenced the transcriptome of the ovary of female zebrafish and a total of 284 overlapping DEGs were obtained. Functional enrichment analysis showed that 284 overlapping DEGs function mainly in complement and coagulation cascades signaling pathways. In addition, we identified genes that may be associated with immunity, such as LOC108191474 and ZGC:173837. We found that exposure to PFOA can cause an inflammatory response that can lead to ovarian damage and delayed oocyte development.

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.

Prevention of Epithelial Ovarian Cancer

Given the challenges with achieving effective and durable treatment for epithelial ovarian cancer, primary prevention is highly desirable. Fortunately, decades of research have provided evidence for several strategies that can be deployed to optimize risk reduction. These include surgery, chemoprevention, and lifestyle factor modifications. These broad categories vary in terms of the magnitude of risk reduction possible, the possible short-term and long-term side effects, the degree of difficulty, and acceptability. Thus, the concept of a risk-based model to personalize preventive interventions is advocated to guide discussion between care providers and women at risk. For women with inherited major gene mutations that greatly increase risk of ovarian cancer, surgical approaches have favorable risk to benefit ratios. Chemoprevention and lifestyle factor modifications portend a lower degree of risk reduction but confer lower risk of undesirable side effects. Since complete prevention is not currently possible, better methods for early detection remain a high priority.

Beyond the pill: contraception and the prevention of hereditary ovarian cancer

BRCA1 and BRCA2 mutation carriers face an elevated lifetime risk of developing ovarian cancer. Oral contraceptives have been shown to significantly decrease the risk of ovarian cancer by approximately 50% in this high-risk population. Changes in contraceptive formulations and patterns of use over time have introduced lower hormonal dosages, different steroid types and non-oral routes of administration. Specifically, there has been a considerable shift in patterns of contraceptive use and the increase in the uptake of non-oral, long-acting, reversible contraception (e.g., intrauterine devices, implants, injections) has corresponded to a decline in oral contraceptive pill use. Whether or not these other methods confer a protective effect against ovarian cancer in the general population is not clear. To our knowledge, there have been no such studies conducted among BRCA mutation carriers. Furthermore, the impact of these changes on the risk of developing ovarian cancer is not known. In this article, we will review the existing epidemiologic evidence regarding the role of contraceptives and the risk of ovarian cancer with a focus on women with a BRCA1 or BRCA2 mutation. We will discuss recent findings and gaps in the knowledge while extrapolating from studies conducted among women from the noncarrier population.

Oral contraceptive use by formulation and breast cancer risk by subtype in the Nurses' Health Study II: a prospective cohort study

BACKGROUND

Oral contraceptive use has been associated with a higher breast cancer risk; however, evidence for the associations between different oral contraceptive formulations and breast cancer risk, especially by disease subtype, is limited.

OBJECTIVE

This study aimed to evaluate the associations between oral contraceptive use by formulation and breast cancer risk by disease subtype.

STUDY DESIGN

This prospective cohort study included 113,187 women from the Nurses' Health Study II with recalled information on oral contraceptive usage from 13 years of age to baseline (1989) and updated data on usage until 2009 collected via biennial questionnaires. A total of 5799 breast cancer cases were identified until the end of 2017. Multivariable Cox proportional hazards models estimated hazard ratios and 95% confidence intervals for the associations between oral contraceptive use and breast cancer risk overall and by estrogen and progesterone receptor and human epidermal growth factor receptor 2 status. Oral contraceptive use was evaluated by status of use (current, former, and never), duration of and time since last use independently and cross-classified, and formulation (ie, estrogen and progestin type).

RESULTS

Current oral contraceptive use was associated with a higher risk for invasive breast cancer (hazard ratio, 1.31; 95% confidence interval, 1.09-1.58) when compared with never use, with stronger associations observed for longer durations of current use (>5 years: hazard ratio, 1.56; 95% confidence interval, 1.23-1.99; ≤5 years: hazard ratio, 1.19; 95% confidence interval, 0.95-1.49). Among former users with >5 years since cessation, the risk was similar to that of never users (eg, >5 to 10 years since cessation: hazard ratio, 0.99; 95% confidence interval, 0.88-1.11). Associations did not differ significantly by tumor subtype. In analyses by formulation, current use of formulations containing levonorgestrel in triphasic (hazard ratio, 2.83; 95% confidence interval, 1.98-4.03) and extended cycle regimens (hazard ratio, 3.49; 95% confidence interval, 1.28-9.53) and norgestrel in monophasic regimens (hazard ratio, 1.91; 95% confidence interval, 1.19-3.06), all combined with ethinyl estradiol, was associated with a higher breast cancer risk when compared with never oral contraceptive use. No association was observed for current use of the other progestin types evaluated (norethindrone, norethindrone acetate, ethynodiol diacetate, desogestrel, norgestimate, and drospirenone), however, sample sizes were relatively small for some of the subgroups, limiting these analyses.

CONCLUSION

Current oral contraceptive use was associated with a higher risk for invasive breast cancer regardless of disease subtype, however, the risk in former users was comparable with never users 5 years after cessation. In analyses by progestin type, associations were observed for select formulations containing levonorgestrel and norgestrel. Assessment of the associations for newer progestin types (desogestrel, norgestimate, drospirenone) was limited by sample size, and further research on more recently introduced progestins is warranted.

Associations of Oral Contraceptives with Mammographic Breast Density in Premenopausal Women

BACKGROUND

We investigated the associations of oral contraceptives (OC) with percent breast density (PD), absolute dense area (DA), nondense area (NDA), and a novel image intensity variation (V) measure in premenopausal women.

METHODS

This study included 1,233 controls from a nested case-control study within Nurses' Health Study II cohort. Information on OCs was collected in 1989 and updated biennially. OC use was defined from the questionnaire closest to the mammogram date. PD, DA, and NDA were measured from digitized film mammograms using a computer-assisted thresholding technique; the V measure was obtained with a previously developed algorithm measuring the SD of pixel values in the eroded breast region. Generalized linear regression was used to assess associations between OCs and density measures (square root-transformed PD, DA, and NDA, and -untransformed V).

RESULTS

OC use was not associated with PD [current vs. never: β = -0.06; 95% confidence interval (CI), -0.37-0.24; past vs. never: β = 0.10; 95% CI, -0.09-0.29], DA (current vs. never: β = -0.20; 95% CI -0.59-0.18; past vs. never: β = 0.13; 95% CI, -0.12-0.39), and NDA (current vs. never: β = -0.19; 95% CI, -0.56-0.18; past vs. never: β = -0.01; 95% CI, -0.28-0.25). Women with younger age at initiation had significantly greater V-measure (<20 years vs. never: β = 26.88; 95% CI, 3.18-50.58; 20-24 years vs. never: β = 20.23; 95% CI, -4.24-44.71; 25-29 years vs. never: β = 2.61; 95% CI -29.00-34.23; ≥30 years vs. never: β = 0.28; 95% CI, -34.16-34.72, P _trend = 0.03).

CONCLUSIONS

Our findings suggest that an earlier age at first OC use was associated with significantly greater V.

IMPACT

These findings could guide decisions about the age for OC initiation.

Contemporary hormonal contraception and cervical cancer in women of reproductive age

To determine cervical cancer risk associated with contemporary hormonal contraceptives, we conducted a cohort study of women aged 15 to 49 living in Denmark from 1995 to 2014, using routinely collected information about redeemed prescriptions, incident cancer and potential confounders. Poisson regression calculated adjusted cervical cancer risks among different contraceptive user groups by duration of use, time since last use, hormonal content and cancer histology. During >20 million person-years, 3643 incident cervical cancers occurred. Ever users of any hormonal contraceptives compared to never users had a relative risk (RR) of 1.19 (95% confidence interval [CI] 1.10-1.29). Increased risks were seen in current or recent users of any hormonal: RR 1.30 (95% CI 1.20-1.42) and combined: RR 1.40 (95% CI 1.28-1.53), but not progestin-only contraception: RR 0.91 (95% CI 0.78-1.07). Current or recent users of any hormonal contraception had an increased risk of both adenocarcinoma (RR 1.29, 95% CI 1.05-1.60) and squamous cancer (RR 1.31, 95% CI 1.19-1.44). The risk pattern among any hormonal and combined contraceptive users generally increased with longer duration of use and declined after stopping, possibly taking longer to disappear among prolonged users. Combined products containing different progestins had similar risks. Approximately one extra cervical cancer occurred for every 14 700 women using combined contraceptives for 1 year. Most women in our study were not vaccinated against human papillomavirus (HPV) infections. Our findings reinforce the urgent need for global interventions such as systematic screening, treatment of cervical intraepithelial neoplasia and HPV vaccination programmes to prevent cervical cancer, especially among users of combined contraceptives.

Oral contraceptive use by formulation and endometrial cancer risk among women born in 1947-1964: The Nurses' Health Study II, a prospective cohort study

Oral contraceptives (OCs) have been associated with long-term lower endometrial cancer risk; relatively little is known about associations with more recent OC formulations and associations with longer-term risk. A total of 107,069 women from the Nurses’ Health Study II recalled OC use from age 13 to baseline (1989); biennial questionnaires updated data on OC use until 2009. OCs were classified by estrogen and progestin type, dose, and potency based on reported brand. 864 incident endometrial cancer cases were identified through 2017. Multivariable Cox proportional hazards models estimated hazard ratios (HR) and 95% confidence intervals [95% CI] for the association of OC use with endometrial cancer risk. OC use was associated with lower endometrial cancer risk (ever use, HR 0.77 [95% CI 0.65–0.91]; >10 years of use, 0.43 [0.32–0.58] vs. never OC use). Inverse associations for duration were evident regardless of time since last use. Longer durations (> 5 years) of ethinyl estradiol (0.52 [0.41–0.67]) and second-generation progestins (0.43 [0.30–0.61]), both versus never use, were more strongly associated with lower risk than mestranol (0.66 [0.50–0.88], p-het = 0.01) and first-generation progestins (0.62 [0.49–0.78], p-het = 0.03). Inverse associations were generally observed for cross-classified cumulative average estrogen and progestin dose and potency (< vs. ≥ median; ever use vs. never OC use), with the exception of high estrogen and low progestin dose. OCs were associated with lower endometrial cancer risk, independent of time since last use. Use of ethinyl estradiol and second-generation progestins were more strongly inversely associated with risk compared with older formulations.

What are the mechanisms of action of the different contraceptive methods to reduce the risk of ovarian cancer?

OBJECTIVE

Ovarian cancer (OvCa) is the deadliest gynaecologic malignancy. Knowing that OvCa, as a disease, has different origins has allowed us to relate them to the mechanisms of action of different contraceptive methods with the aim of evaluating the possibility of their use in reducing risk.

STUDY DESIGN

This commentary review article will instead focus on the recent findings on the role of contraceptive methods in preventing of OvCa.

RESULTS

Combined hormonal contraceptive (CHC) use is an effective method of chemoprevention for OvCa in the general population and in women with genetic disorders. Salpingectomy, better than tubal ligation, should be offered for ovarian/tubal/peritoneal cancer prevention. Progestogen-only methods can decrease the risk of OvCa via reduced menstrual bleeding and by changes in the hormonal environment that surrounds the ovary. IUDs of any type, through different mechanisms, decrease the risk of OvCa. Barrier methods prevent the passage of germs into the tubes and ovaries and the inflammatory state they produce.

CONCLUSIONS

Most contraceptive methods have a mechanism of action that may favour a reduction in the risk of OvCa. The theories of incessant ovulation, retrograde menstruation, and that the fallopian tubes are the site of origin of a proportion of high-grade serous OvCa, have led to the recommendation that anovulatory methods, those that decrease menstrual bleeding, and those that blocked tubes, or even better, 'opportunistic salpingectomy' are a current approach to prevent OvCa in the population general and, above all, in the population at risk.

Transcription factors in epithelial ovarian cancer: histotype-specific drivers and novel therapeutic targets

Transcription factors (TFs) are major contributors to cancer risk and somatic development. In preclinical and clinical studies, direct or indirect inhibition of TF-mediated oncogenic gene expression profiles have proven to be effective in many tumor types, highlighting this group of proteins as valuable therapeutic targets. In spite of this, our understanding of TFs in epithelial ovarian cancer (EOC) is relatively limited. EOC is a heterogeneous disease composed of five major histologic subtypes; high-grade serous, low-grade serous, endometrioid, clear cell and mucinous. Each histology is associated with unique clinical etiologies, sensitivity to therapies, and molecular signatures - including diverse transcriptional regulatory programs. While some TFs are shared across EOC subtypes, a set of TFs are expressed in a histotype-specific manner and likely explain part of the histologic diversity of EOC subtypes. Targeting TFs present with unique opportunities for development of novel precision medicine strategies for ovarian cancer. This article reviews the critical TFs in EOC subtypes and highlights the potential of exploiting TFs as biomarkers and therapeutic targets.

Estimated Number of Lifetime Ovulatory Years and Its Determinants in Relation to Levels of Circulating Inflammatory Biomarkers

Reproductive events, such as ovulation, trigger an inflammatory cascade. Few studies have examined their long-term influence on inflammatory profiles. We included 3,393 premenopausal and 3,915 postmenopausal women with intact ovaries/uterus from the Nurses' Health studies (Nurses' Health Study (1989-1990) and Nurses' Health Study II (1996-1999)) in an analysis of the association between lifetime ovulatory years (LOY) and levels of inflammatory biomarkers. We estimated LOY as age at menopause (age at blood collection for premenopausal women) minus age at menarche, subtracting years of oral contraceptive (OC) use and 1 year per pregnancy. After adjustment for other inflammation-related factors (e.g., body mass index, exercise, diet), every 5-year increase in LOY was associated with lower C-reactive protein (CRP) levels in both premenopausal (difference = -11.5%, 95% confidence interval: -15.0, -8.0; P < 0.0001) and postmenopausal (difference = -7.2%, 95% confidence interval: -10.0, -4.3; P < 0.0001) women. Older age at menopause (P = 0.007), earlier menarche (P = 0.007), and shorter duration of OC use (P = 0.002) were associated with lower CRP levels in postmenopausal women, whereas duration of OC use was positively associated with CRP levels in premenopausal women (P < 0.0001). LOY was modestly inversely associated with interleukin 6 in postmenopausal women (P = 0.03). Notably, the associations of CRP with LOY were similar in magnitude to associations with exercise and a healthy diet, though weaker than the association with body mass index. Although many reproductive events induce acute inflammation, increased LOY was associated with lower chronic systemic inflammation even after menopause.

Long-Term Follow-Up after Surgical Management for Atypical Endometriosis: A Series of Nine Cases

Background and Objective

Atypical endometriosis is reported to possess a precancerous potential attributed to premalignant changes characterized by cytological atypia and architecture proliferation. Although the coexistence of atypical endometriosis and neoplasms has been reported, cases of atypical endometriosis transformation to carcinoma are rarely reported. The purpose of this case series was to evaluate the prognosis of atypical endometriosis.

Subjects and Methods

Data from nine women who underwent surgical treatment including cystectomy and salpingo-oophorectomy with or without hysterectomy and diagnosed with atypical endometriosis was analyzed. Between January 2006 and January 2018, the clinical characteristics and prognosis of atypical endometriosis were evaluated.

Results

During the follow-up period, eight of nine patients with atypical endometriosis did not develop malignant epithelial tumors, although one patient developed endometrioid carcinoma, grade 1, 48 months after her right laparoscopic cystectomy. The median overall survival period for all patients was 68 (range 13–131) months.

Conclusion

When we encounter the cases of atypical endometriosis, it is necessary to consider the possibility of ovarian cancer and carefully follow those cases for long periods.

Association between contemporary hormonal contraception and ovarian cancer in women of reproductive age in Denmark: prospective, nationwide cohort study

OBJECTIVES

To investigate the association between contemporary combined hormonal contraceptives (including progestogen types in combined preparations and all progestogen-only products) and overall and specific types of ovarian cancer.

DESIGN

Prospective, nationwide cohort study.

SETTING

Denmark, 1995-2014.

PARTICIPANTS

All women aged 15-49 years during 1995-2014 were eligible. Women were excluded if they immigrated after 1995, had cancer (except non-melanoma skin cancer), had venous thrombosis, or were treated for infertility before entry (final study population included 1 879 227 women). Women were categorised as never users (no record of being dispensed hormonal contraception), current or recent users (≤1 year after stopping use), or former users (>1 year after stopping use) of different hormonal contraceptives.

MAIN OUTCOME MEASURES

Poisson regression was used to calculate relative risk of ovarian cancer among users of any contemporary combined hormonal contraceptives and by progestogen type in combined preparations and all progestogen-only products, including non-oral preparations. Separate analyses examined women followed up to their first contraception type switch and those with full contraceptive histories. Duration, time since last use, and tumour histology were examined and the population prevented fraction were calculated.

RESULTS

During 21.4 million person years, 1249 incident ovarian cancers occurred. Among ever users of hormonal contraception, 478 ovarian cancers were recorded over 13 344 531 person years. Never users had 771 ovarian cancers during 8 150 250 person years. Compared with never users, reduced risks of ovarian cancer occurred with current or recent use and former use of any hormonal contraception (relative risk 0.58 (95% confidence interval 0.49 to 0.68) and 0.77 (0.66 to 0.91), respectively). Relative risks among current or recent users decreased with increasing duration (from 0.82 (0.59 to 1.12) with ≤1 year use to 0.26 (0.16 to 0.43) with >10 years' use; P<0.001 for trend). Similar results were achieved among women followed up to their first switch in contraceptive type. Little evidence of major differences in risk estimates by tumour type or progestogen content of combined oral contraceptives was seen. Use of progestogen-only products were not associated with ovarian cancer risk. Among ever users of hormonal contraception, the reduction in the age standardised absolute rate of ovarian cancer was 3.2 per 100 000 person years. Based on the relative risk for the never use versus ever use categories of hormonal contraception (0.66), the population prevented fraction was estimated to be 21%-that is, use of hormonal contraception prevented 21% of ovarian cancers in the study population.

CONCLUSIONS

Use of contemporary combined hormonal contraceptives is associated with a reduction in ovarian cancer risk in women of reproductive age-an effect related to duration of use, which diminishes after stopping use. These data suggest no protective effect from progestogen-only products.

Current Gaps in Ovarian Cancer Epidemiology: The Need for New Population-Based Research

With recent ovarian cancer screening studies showing no clinically significant mortality benefit, preventing this disease, identifying high-risk populations, and extending survival remain priorities. However, several challenges are impeding progress in ovarian cancer research. With most studies capturing exposure information from 10 or more years ago, evaluation of how changing patterns of exposures, such as new oral contraceptive formulations and increased intrauterine device use, might influence ovarian cancer risk and survival is difficult. Risk factors for ovarian cancer should be evaluated in the context of tumor histotypes, which have unique molecular features and cells of origin; this is a task that requires large collaborative studies to achieve meaningful sample sizes. Importantly, identification of novel modifiable risk factors, in addition to those currently known to reduce risk (eg, childbearing, tubal ligation, oral contraceptive use), is needed; this is not feasibly implemented at a population level. In this Commentary, we describe important gaps in knowledge and propose new approaches to advance epidemiologic research to improve ovarian cancer prevention and survival, including updated classification of tumors, collection of data on changing and novel exposures, longer follow-up on existing studies, evaluation of diverse populations, development of better risk prediction models, and collaborating prospectively with consortia to develop protocols for new studies that will allow seamless integration for future pooled analyses.