Epidemiology of ovarian cancer: a review

Our plain-English summary of Epidemiology of ovarian cancer: a review, by B.M. Reid, J.B. Permuth, T.A. Sellers (Cancer Biology & Medicine, 2017).

The study

• Authors: B.M. Reid, J.B. Permuth, T.A. Sellers
• Journal: Cancer Biology & Medicine
• Published: 2017;14(1):9-32
• Cited by: 1,101 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Ovarian cancer (OC) is the seventh most commonly diagnosed cancer among women in the world and the tenth most common in China. Epithelial OC is the most predominant pathologic subtype, with five major histotypes that differ in origination, pathogenesis, molecular alterations, risk factors, and prognosis. Genetic susceptibility is manifested by rare inherited mutations with high to moderate penetrance. Genome-wide association studies have additionally identified 29 common susceptibility alleles for OC, including 14 subtype-specific alleles. Several reproductive and hormonal factors may lower risk, including parity, oral contraceptive use, and lactation, while others such as older age at menopause and hormone replacement therapy confer increased risks. These associations differ by histotype, especially for mucinous OC, likely reflecting differences in etiology. Endometrioid and clear cell OC share a similar, unique pattern of associations with increased risks among women with endometriosis and decreased risks associated with tubal ligation. OC risks associated with other gynecological conditions and procedures, such as hysterectomy, pelvic inflammatory disease, and polycystic ovarian syndrome, are less clear. Other possible risk factors include environmental and lifestyle factors such as asbestos and talc powder exposures, and cigarette smoking. The epidemiology provides clues on etiology, primary prevention, early detection, and possibly even therapeutic strategies.

In plain English

This article was a review, not a new study. The authors summarized published research on epithelial ovarian cancer, including inherited genes, reproductive and hormonal factors, contraception, gynecological conditions, and lifestyle and environmental factors such as asbestos and talcum powder. On asbestos, they wrote that human and animal studies have found asbestos fibers in ovaries, but that a link with ovarian cancer had not been firmly established. This was partly because few exposed women were studied and because peritoneal mesothelioma is often misdiagnosed as ovarian cancer on death certificates. They reported that an earlier meta-analysis of fourteen cohort and two case-control studies found an effect size of 1.75 (95% CI 1.45 to 2.10) in asbestos-exposed women. The figure fell to 1.29 (95% CI 0.97 to 1.73) among studies of pathologically confirmed cases. They noted that, despite this lack of consistency, the International Agency for Research on Cancer (IARC) has called the human evidence that asbestos causes ovarian cancer 'sufficient'. For genital talc use they described conflicting results and a 2006 IARC classification as possibly carcinogenic. The authors concluded that additional causes of ovarian cancer are yet to be identified.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Narrative review of published epidemiological research (no new data collected)
• Who was studied: Published studies of ovarian cancer, focusing on epithelial ovarian cancer, from many countries. The review itself studied no participants.
• Exposure: Many suspected risk and protective factors: genetics, reproductive and hormonal factors, gynecological conditions and surgery, contraception, hormone replacement therapy, obesity, diet, physical activity, smoking, alcohol, asbestos and talcum powder, and drugs. No asbestos fiber types are named. For talc, the exposure discussed is genital use of talcum powder.
• Main results:
  • The authors reported that human and animal studies have found asbestos fibers in the ovaries.
  • The authors stated that a link between asbestos exposure and ovarian cancer has not been firmly established. They gave two reasons: small numbers of exposed women, and disease misclassification (peritoneal mesothelioma often misdiagnosed as ovarian cancer on death certificates).
  • A prior systematic review and meta-analysis of fourteen cohort and two case-control studies, cited by the authors, found a statistically significant 75% excess risk of ovarian cancer in women exposed to asbestos (effect size=1.75, 95% CI: 1.45 to 2.10).
  • In that same meta-analysis, the association was attenuated among studies of cancer incidence based on pathologically confirmed cases (effect size=1.29, 95% CI: 0.97 to 1.73).
  • The authors stated that, despite the lack of consistency, IARC has declared the evidence in humans 'sufficient' that asbestos exposure causes ovarian cancer.
  • For genital talc use, the authors cited a 2006 meta-analysis of 21 studies that reported an approximately 35% increase in risk.
  • The authors also cited conflicting talc studies. The Women's Health Initiative reported a null association in a cohort of 61,576 post-menopausal women. A case-control study by Cramer and colleagues reported increased risk among talc users (OR=1.3, 95% CI: 1.16 to 1.52).
  • The authors reported that IARC classified genital talc use as possibly carcinogenic to humans in 2006.
• The authors' conclusion: The authors concluded that, apart from highly penetrant gene mutations, established risk factors neither confer large increases in risk nor explain all the variability in incidence. They concluded that additional causes of ovarian cancer are yet to be identified.

Topics

Medical terms in this study, explained in our Lexicon: Epidemiology, Ovarian Cancer, Prognosis, Germline Mutation, Etiology, Talc.

Related studies

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• Perineal talc use and ovarian cancer risk: a case study of scientific standards in environmental epidemiology — M. Huncharek, J. Muscat (2011)
• Assessing Tumor-Infiltrating Lymphocytes in Solid Tumors: A Practical Review for Pathologists and Proposal for a Standardized Method from the International Immuno-Oncology Biomarkers Working Group: Part 2: TILs in Melanoma, Gastrointestinal Tract Carcinomas, Non-Small Cell Lung Carcinoma and Mesothelioma, Endometrial and Ovarian Carcinomas, Squamous Cell Carcinoma of the Head and Neck, Genitourinary Carcinomas, and Primary Brain Tumors — S. Hendry, R. Salgado, et al. (2017)
• Possible role of ovarian epithelial inflammation in ovarian cancer — R.B. Ness, C. Cottreau (1999)
• Ovarian cancer and talc: a case-control study — D.W. Cramer, W.R. Welch, et al. (1982)

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