Are Women with Breast Cancer at an Increased Risk of Developing Ovarian Cancer?

The number of women diagnosed with breast cancer who are later diagnosed with ovarian cancer is very low. However, the short answer is yes — having breast cancer does indicate you might be at an increased risk of ovarian cancer. We are just beginning to understand why.^1,2

Ovarian Cancer and Breast Cancer Statistics in the US

All stats are from seer.cancer.gov and based on 2018–2021 data, excluding 2020.

• Lifetime risk of a woman developing ovarian cancer is 1.1%¹³
• Lifetime risk of a woman developing breast cancer is 13.1%¹⁴

Researchers at the University of Cambridge published data in 2024 that analyzed data from more than 580,000 breast cancer survivors from the UK, finding they had a 25% greater risk of developing ovarian cancer than the UK general population.¹⁵ So for example, if you took the US lifetime rate and increased it by 25%, that would equate to about a 1.4% ovarian cancer risk overall for breast cancer survivors.

Breast cancer does not cause ovarian cancer, but the risk for the two appear to be linked. The links between the two cancers may be reproductive hormones and/or hereditary genetic variants. In this post, we’ll give you a brief overview of ovarian cancer, and then discuss research that shows a link between breast and ovarian cancer.

Ovarian cancer overview

Ovaries, oval-shaped glands, are located on either side of the uterus and connected to it by the fallopian tubes. They develop eggs (ova) and produce estrogen and progesterone for reproduction. Ovarian cancer can develop in the ovaries, fallopian tubes, or nearby tissue.²

The symptoms of ovarian cancer may include feeling bloated or easily satiated, pelvic, back, or abdominal pain, abnormal vaginal bleeding, menstruation, and urine or bowel changes. Many of these symptoms can be attributed to other health issues, so knowing what is normal for you is important. Don’t hesitate to discuss changes with your doctor.

What risk factors may contribute to the development of ovarian cancer?³

• Age
• Family history
• Lifestyle factors, like smoking, and being overweight
• Inherited genetic variants – like BRCA and the KRAS-variant
• First full-term pregnancy after age 35 or never carrying a pregnancy to term
• A personal history of breast cancer

The link between breast cancer and ovarian cancer

Inherited Genetic Variants

Several inherited genetic variants can be linked to both breast and ovarian cancer. If you have one of these variants, you have an increased risk of developing one or both of these cancers.⁴ These genetic links are often found by studying families where multiple members have breast/ovarian cancer and are often described as having Hereditary Breast and Ovarian Cancer Syndrome (HBOC).⁵

Some of the inherited genetic variants linked to both breast and ovarian cancer:^4,6

• BRCA 1 & 2
• KRAS-Variant
• Lynch Syndrome
• ATM mutations
• MMR mutations

The KRAS-variant is associated with breast, ovarian, lung, and other cancers, and the development of multiple cancers in the same person.

Reproductive Hormones

Both breasts and ovaries are part of the reproductive system, and so both are affected by the same hormones, especially estrogen. The presence or absence of estrogen has been shown to drive breast cancer development.⁷

Breast Cancer, Ovarian Cancer, and the KRAS-variant

A 2012 paper, led by a researcher from the Ohio State University Comprehensive Cancer Center and Department of Internal Medicine, studied women with both breast and ovarian cancer and evaluated the association with the KRAS-variant.⁸

Of patients in this study with both breast and ovarian cancer, 49% of them had a BRCA mutation. As the KRAS-variant is linked to both breast and ovarian cancer, the study investigated how many of the remaining 51% of patients had the KRAS-variant.

Out of the 232 patients studied, they found:

1. 21% had the KRAS-variant
2. No ethnic link was found
3. Having a BRCA mutation was not linked to having the KRAS-variant
4. Those with the KRAS-variant were more likely to develop ovarian cancer after menopause
5. Those with the KRAS-variant were 29.2% more likely to have a positive family history of cancer
6. There was an increased risk of developing multiple primary cancers, in addition to breast and ovarian cancer, for those with the KRAS-variant

The research indicated that:

1. For patients with both breast and ovarian cancer and who test negative for a BRCA mutation, the KRAS-variant is often found.
2. Based on this finding, breast cancer patients who are concerned about ovarian cancer and negative for BRCA mutations may consider being tested for the KRAS-variant.
3. Since breast cancer is generally diagnosed before ovarian cancer in women with the KRAS-variant, there may be opportunities for prevention.

Of particular note in the study is the link between the KRAS-variant, breast cancer, and ovarian cancer after menopause, which may point to a hormonal connection.

In our research, a link between the reproductive hormone estrogen and the KRAS-variant has shown that for women who carry the KRAS-variant, maintaining estrogen can help protect against developing breast cancer.⁷ At this time it is unknown if the same holds true for preventing ovarian cancer for women with the KRAS-variant. Another challenge in studying a possible association between estrogen loss and ovarian cancer for KRAS-variant patients is that breast cancer management often includes estrogen reduction. How to best manage these potential issues for patients with the KRAS-variant, and other questions, are currently being studied.

Lowering your risk of developing ovarian cancer after breast cancer

There are things you can do to decrease your risk of ovarian cancer after a breast cancer diagnosis.

Know the risk factors you can change

• Don’t smoke
• Maintain a healthy weight
• Eat healthy

Better understand your risk level

• Find out what cancers run in your family
• Ask your provider to either order you genetic testing or refer you to a geneticist to discover your genetic risk
• Test for the KRAS-variant

Make a plan based on your risk level

• Decide on when and how much screening you need
• Continue to see your OBGYN, as that’s the best way to screen and/or manage your ovaries
• Continue to follow our research

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Further Reading

• Why you should get your KRAS-variant results
• What You Need to Know About Estrogen and the KRAS-variant – MiraKind
• Menopause & Myths about Hormone Replacement Therapy – MiraKind
• Let’s learn more about Hormone Replacement Therapy – together! – MiraKind
• Understanding the different causes of cancer: genetic variants vs. genetic mutations

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References

1. What Are Second Cancers? 
2. Ovarian Cancer Basics 
3. Ovarian Cancer Risk Factors 
4. Association of Breast and Ovarian Cancers With Predisposition Genes Identified by Large-Scale Sequencing 
5. Evaluating genetic association among ovarian, breast, and endometrial cancer: evidence for a breast/ovarian cancer relationship. – PMC
6. Risks and causes of ovarian cancer 
7. Breast Cancer Hormone Receptor Status | Estrogen Receptor
8. The KRAS-Variant Is Associated with Risk of Developing Double Primary Breast and Ovarian Cancer | PLOS ONE 
9. Estrogen-Dependent Cancers: Causes, Diagnosis & Treatment 
10. Full article: Estrogen withdrawal, increased breast cancer risk and the KRAS-variant 
11. Temporal Trends in Second Cancer Risks Based on SEER Data – NCI 
12. Multiple Primary Cancer Monograph – NCI
13. Cancer Stat Facts: Ovarian Cancer
14. Cancer Stat Facts: Female Breast Cancer
15. Study highlights increased risk of second cancers among breast cancer survivors | University of Cambridge