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New research to investigate why breastfeeding reduces the risk of developing breast cancer

Researchers will investigate the relationship between breastfeeding and breast cancer, thanks to new funding from Breast Cancer Now.

Breastfeeding has been linked to a lower risk of developing breast cancer, with previous data analysis showing the risk of developing the disease decreases by 4.3 per cent for every 12 months a woman breastfeeds*.

However, it is not exactly clear why breastfeeding lowers breast cancer risk. It could be because breastfeeding can alter the balance of hormones in the body, or it might affect breast cells to make them less prone to changes that could lead to cancer.

Breast Cancer Now has awarded funding of £150,715 to Dr James Flanagan and his team at Imperial College London, who want to better understand how breastfeeding might protect against breast cancer. In particular, they want to investigate how the length of time a woman breastfeeds for affects her breast cancer risk.

In previous research, Dr Flanagan and his team found breast milk contained cells which sometimes had potentially cancer-causing changes, but they only found these cells in the milk of women who had breastfed for under four months.

Now, the researchers want to see if breastfeeding for longer periods of time removes these cells. No risk is posed to the baby by consuming these cells as they are destroyed in the stomach.

The team also want to find out whether factors such as weight, exercise, or smoking are associated with the presence of these cells.

Using breast milk samples donated by 300 women taking part in the Breastmilk Epigenetics Cohort Study (BECS), coordinated in partnership with the Human Milk Foundation***, the researchers will screen for these cells with potentially cancer-causing changes in their DNA.

They’ll collect samples every few months from the same women to see if changes that were initially detected are reduced in later milk samples. All women who donate milk to the Hearts Milk Bank, part of the Human Milk Foundation, will be offered the chance to take part.

The team will also interview some of the women in the study to find out whether they would want to be made aware of the detection of DNA changes in their breast milk and how they might feel about public health messaging that conveys they could be at greater risk.

With only 48 per cent of women continuing to breastfeed beyond 6-8 weeks in the UK**, the researchers are keen to understand if women would want to know if they were potentially at risk of breast cancer and, if so, if and how it might impact their decision around how long to breastfeed for.

Dr James Flanagan, Reader in Epigenetics at Imperial College London’s Department of Surgery and Cancer, said: “We believe that preventing breast cancer is the best way to reduce the number of women dying from the disease, and in order to do this, we need to understand what things women could do to reduce their risk. In this study, we aim to find out why breastfeeding can lower breast cancer risk and use this knowledge to prevent as many breast cancers as possible.”

Professor Amy Brown at Swansea University, a collaborator on this project, said: “This research question is so important in advancing our knowledge of how to reduce breast cancer risk, but we also know that it can be a difficult topic for many women who weren’t able to breastfeed or who didn’t receive the support they needed. We want to explore how women might feel if they are at greater risk of breast cancer but may or may not be able to breastfeed, or how women may feel about connecting their experience of feeding their baby alongside their perception of breast cancer risk.”

Dr Simon Vincent, Breast Cancer Now’s director of research, support and influencing said: “Breastfeeding can slightly reduce the risk of developing breast cancer, and we know that the longer a woman breastfeeds, the more her risk is lowered, but it’s not yet fully understood why.

“With 55,000 women diagnosed with breast cancer every year in the UK, and this number expected to rise to 69,000 diagnoses a year by 2030, we need to fully understand how breastfeeding can influence this risk. While we are very aware that breastfeeding isn’t an option for all women and that this is a sensitive topic, we’re delighted to fund more research in this area as it will help us continue to improve the information and advice that we provide women on breast cancer risk.”

Breast Cancer Now is the research and support charity here for anyone affected by breast cancer. Call their free helpline on 0808 800 6000 to speak to their expert nurses or find out more and donate at


For more information or to arrange an interview, please contact the Breast Cancer Now press office at or call 07436 107914.

Notes to editors


*Breast cancer and breastfeeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50 302 women with breast cancer and 96 973 women without the disease - The Lancet

** Accessed: 11/01/2024


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