Is endometriosis linked to ovarian cancer risk? Significant new research suggests so, but we still need the full picture. 

Trigger Warning:

At the OCRF we understand that this may come as concerning for people in the community who have endometriosis. If this new information raises questions for you, we encourage you to reach out to a trusted medical professional to seek advice appropriate to your unique circumstances. 

A large population-based study suggests the risk of developing some ovarian cancer subtypes is higher among those with endometriosis, particularly higher stage endometriosis.  

Researchers from the University of Utah analysed the medical records, across 27 years, of more than 450,000 people: 78,000 of whom had endometriosis. The published findings¹ calculated an increased risk between endometriosis and some subtypes of ovarian cancer. Some of these ovarian cancer subtypes had not previously been shown to be linked to endometriosis. While this study offers additional and compelling insights into links between these two conditions, further investigation is required. 

You may have already heard about links between ovarian cancer risk and endometriosis — but there are many subtypes of ovarian cancer, and several stages of endometriosis. This study sheds some light on risk factors for some ovarian cancer subtypes.  

How much does endometriosis increase the risk of ovarian cancer subtypes? 

The study determined that those with endometriosis are overall four times more likely to develop epithelial ovarian cancer. Other studies had previously associated endometriosis with an increased risk of certain subtypes of epithelial ovarian cancer, including endometroid, clear cell and low-grade serous^2-4, however this is one of the first to link endometriosis with an increased risk of high-grade serous ovarian cancer.  

Broken down further, those with endometriosis were found to be: 

• Approximately 7.5  times more likely to develop type I epithelial ovarian cancer (including endometrioid, clear cell, mucinous, and low-grade serous)  
• 2.7 times more likely to develop type II epithelial ovarian cancer (high-grade serous). This a significant finding as high-grade serous is the most common and aggressive subtype of ovarian cancer, accounting for approximately 70 per cent of ovarian cancer diagnoses⁵. 

Some types of endometriosis presented as higher risk factors for ovarian cancer than others

Endometriosis is a chronic disease that involves growth of tissue, similar to the lining of the uterus, in other areas of the body.  Endometriosis can commonly occur in the peritoneum (abdominal cavity lining), outside of the uterus, the bowel and ovaries, but it can be present on any organ. Broadly speaking endometriosis can be defined as superficial (involving shallow invasion of the endometriosis into the underlying tissue) or deep infiltrating (deep invasion of organs within or outside the pelvis)⁶. The Utah researchers found that: 

• Superficial peritoneal endometriosis was associated with 2.82 times higher risk of developing epithelial ovarian cancer.  
• Deep infiltrating endometriosis and/or ovarian endometriomas had 9.66 times the risk of epithelial ovarian cancer overall. This was categorised by a 19-fold increased risk of type I epithelial ovarian cancer, and a four-fold risk of type II epithelial ovarian cancer. 

Although this was a large-scale study, it’s important to note that over 90 per cent of the medical records analysed belonged to people of Caucasian ethnicity and the OCRF consider it vital that further research with greater inclusion, be conducted. It’s also important to note that only epithelial (the most common sub-category) of ovarian cancer was assessed, not stromal or germ cell tumour ovarian cancers. Additionally, the study didn’t indicate whether germline, BRCA1/2 genetic mutations or homologous recombinant deficiency (a type of tumour characteristic), impacted risk.

It is important to emphasise that even for those with endometriosis, the overall risk of developing ovarian cancer remains relatively low despite these confronting findings. Associate Magda Simonis was quoted by the Royal Australasian College of General Practitioners in newsGP highlighting this perspective.  

‘For those suffering from endometriosis, it is important to note that the lifetime risk for developing ovarian cancer is low with approximately 1.9%, as compared to 1.4% for the general population, since ovarian cancer is not frequent when compared to other cancers,’ she said. 

The pain points for ovarian cancer and endometriosis: a clear signal to invest in research across both diseases 

In Australia, endometriosis impacts 1 in 9 girls, women and those assigned female at birth⁷— so, importantly, this study increases our understanding of associations between endometriosis and ovarian cancer risk.  

Although endometriosis is prevalent and ovarian cancer has a low survival rate, research into both diseases has been historically underfunded. By demonstrating an increased risk of ovarian cancer for those with endometriosis, this study has identified an additional higher-risk population that may benefit from much-needed ovarian cancer screening methods. The OCRF is currently supporting diverse research approaches to early detection and identifying those at increased risk.   

Symptoms and pain caused by either ovarian cancer or endometriosis can be vague and varied. This can lead to a lack of recognition of the pain and therefore, a lack of effective and optimal treatment. Because there is no non-invasive diagnostic test for either disease, understanding and placing a greater importance on addressing the pain of those including women, transgender men, intersex, non-binary and gender-diverse individuals and all those who may be impacted by these diseases, is at the heart of detecting them. With the help of our OCRF ambassadors, we recently submitted to the Victorian Government’s Inquiry into Women’s Pain, signalling the vital importance of pain recognition and investment. 

Research⁸ also suggests that conducting molecular assessment and genetic profiling of those with endometriosis and ovarian cancer, and comparing results to those with endometriosis but without ovarian cancer, could help identify why there is an increased risk and correlation between these conditions and lead to risk reduction strategies. Research into both endometriosis is ongoing and new evidence can arise at any time. For instance, researchers at Fondazione IRCCS Istituto Nazionale dei Tumori in Italy have recently indicated¹⁰ that those with clear cell or endometrioid ovarian cancer subtypes can have better survival rates compared to those with these subtypes of ovarian cancer who do not have endometriosis, even after adjusting for potential confounding factors.  

These published findings represent a clear signal that the connection between ovarian cancer and endometriosis demand further investigation. Both areas deserve dedicated, long-term funding and research. We will advocate to see further studies build on these findings, ultimately providing a clearer picture of comprehensive risk to inform improved risk reducing strategies for the community.  

You might also be interested in reading:

Is there a connection between ovarian cancer and endometriosis? 

References: 

1. Barnard et al. 2024, “Endometriosis Typology and Ovarian Cancer Risk”, JAMA, doi:10.1001/jama.2024.9210, published online July 17, 2024 
2. Kvaskoff, M. et al. Endometriosis and cancer: a systematic review and meta-analysis. Human Reproduction Update 27, 393-420 (2020). https://doi.org/10.1093/humupd/dmaa045  
3. Saavalainen, L. et al. Risk of Gynecologic Cancer According to the Type of Endometriosis. Obstet Gynecol 131, 1095-1102 (2018). https://doi.org/10.1097/aog.0000000000002624  
4. Al-Badawi, I. A. et al. Association between Endometriosis and the Risk of Ovarian, Endometrial, Cervical, and Breast Cancer: A Population-Based Study from the U.S. National Inpatient Sample 2016-2019. Curr Oncol 31, 472-481 (2024). https://doi.org/10.3390/curroncol31010032  
5. Biology driven therapy advances in high grade ovarian cancer: Journal of Clinical Investigation, Wang et al. 2024: https://www.jci.org/articles/view/174013  
6. Imperiale L, Nisolle M, Noël JC, Fastrez M. Three Types of Endometriosis: Pathogenesis, Diagnosis and Treatment. State of the Art. J Clin Med. 2023 Jan 28;12(3):994. doi: 10.3390/jcm12030994. PMID: 36769642; PMCID: PMC9918005. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9918005/ 
7. Department of Health and Aged Care, accessed 2024: https://www.health.gov.au/topics/chronic-conditions/what-were-doing-about-chronic-conditions/what-were-doing-about-endometriosis 
8. Australian Institute of Health and Welfare, https://www.aihw.gov.au/news-media/media-releases/2023/2023-september/1-in-7-australian-women-aged-44-49-have-endometriosis#:~:text=Around%2014%25%20of%20women%20aged,Welfare%20(AIHW)%20has%20revealed.  
9. McHale, M. T. New Insights in Endometriosis Subtypes and Ovarian Cancer Risk. JAMA (2024). https://doi.org/10.1001/jama.2024.12357 
10. Leone Roberti Maggiore U, Bogani G, Paolini B, et al Endometriosis-associated ovarian cancer: a different clinical entity International Journal of Gynecologic Cancer 2024;34:863-870.