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Protective immune cells in breastfeeding women guard against breast cancer, research finds
Women who breastfeed develop protective immune cells that help guard against breast cancer, with effects lasting for more than 30 years, new research shows.
The study found that specialised T-cells — immune cells that fight disease — remain in breast tissue long after pregnancy and provide lasting protection, particularly against triple-negative breast cancer, one of the most aggressive forms.
Observations dating back to the 18th century, when physicians noticed nuns had some of the highest rates of breast cancer, first hinted that childbearing and breastfeeding could protect against the disease.
Modern research has confirmed this link, though the biological explanation was unclear.
Professor Sherene Loi is senior author and clinician scientist at the Peter MacCallum Cancer Centre.
The researcher said: “The key take-home messages are that pregnancy and breastfeeding will leave behind long-lived protective immune cells in the breast and the body, and these cells help to reduce risk and improve defence against breast cancer, particularly triple-negative breast cancer, but potentially other cancers as well as disease.”
Researchers from the Peter MacCallum Cancer Centre in Melbourne studied non-cancerous breast tissue from more than 260 women who had undergone breast reduction or preventive surgery.
They found that women who had given birth had more specialised immune cells called CD8⁺ T-cells — part of the adaptive immune system that targets specific threats, including cancer.
The team then tested whether these cells directly provided protection.
In mice, cancer cells implanted into breast tissue grew less in those that had pups and breastfed compared with those that had not. When the researchers removed the T-cells from the nursing mice, the protective effect disappeared.
The researchers also analysed data from more than 1,000 breast cancer patients diagnosed after childbirth with available breastfeeding records.
Women who had breastfed had better outcomes from triple-negative breast cancer than those who had not. Their tumours also contained more immune cells, suggesting ongoing immune activity against the cancer.
The study provides an explanation for why breastfeeding appears protective, and the findings could help inform new strategies for women unable to have children or breastfeed.
Understanding the underlying biology may aid development of vaccines or therapies that mimic this natural defence.
Professor Loi said: “The effects are really quite small for every individual, but population-wide the effects are large.”
She stressed that breastfeeding does not guarantee protection against breast cancer, noting it is “not a 100 per cent guarantee that they won’t get breast cancer.”
The study also explored why some breast cancers contain high numbers of specialised immune cells while others do not.
Patients with more of these cells generally had better outcomes, particularly with triple-negative breast cancer.
Professor Loi explained that T-cells react not only to viruses or bacteria but also to cancer, describing this response as “one of our very modern therapeutic weapons against cancer.”
Associate Professor Wendy Ingman from the University of Adelaide’s Medical School said longer breastfeeding duration provided greater benefits.
Each year of breastfeeding is linked to a 4 per cent lifetime reduction in the mother’s breast cancer risk.
“This study shows that having babies and breastfeeding causes long-lasting changes in immune cells that could help protect the breast from cancer,” Ingman said.
“I’m hopeful that this type of research will lead to new approaches to reduce women’s breast cancer risk.”
A hormone sensor being developed in Australia could help reduce fertility treatment costs and patient pain during IVF.
When preparing for egg collection or an embryo transfer, IVF patients rely on clinicians to closely monitor hormone levels to ensure the procedure is timed precisely when progesterone, oestradiol and luteinising hormone levels are optimal, giving the patient the best chance at conception.
Currently, blood tests are the primary method of measuring progesterone levels, requiring patients to undergo multiple blood draws at a laboratory during certain stages of their menstrual cycle.
However, this approach has several limitations.
For example, if testing falls on a weekend, when most labs are closed, IVF providers are forced to choose a less optimal testing time, potentially affecting treatment precision.
University of Melbourne alumni Edgar Charry and Muhammad Umer, whose partners have lived experience of infertility, created a reproductive health solution by developing a biosensor that can detect progesterone and oestradiol levels using fluid found in the skin, rather than in the blood.
Their startup company Symex Labs has partnered with the University of Melbourne to translate their research into a commercial product.
“Previous research shows nearly all hormones that exist in blood, are also present in interstitial fluid,” said Symex Labs co-founder Charry.
“Interstitial fluid is clear fluid just under the skin that sits between cells, delivering nutrients and carrying away waste.”
“Our biosensor will eventually be worn as a patch and will work by penetrating the skin using small microneedles to attract progesterone molecules in the patient’s interstitial fluid.
“These molecules will bind to the surface of the probe, generating electrical activity. The technology then translates the electrical activity to progesterone levels, ultimately informing the IVF clinical team if the patient is ready for embryo transfer.
“This data will be sent directly to the clinic’s monitoring system, allowing IVF nurses to review the results and advise the patient.”
Monash IVF research director associate professor Mark Green said that, for Monash IVF, the investment in Symex Labs aligns with the company’s focus on innovation and improving the patient journey.
“This technology will save patients time and money as they can conveniently wear the patch in the comfort of their own home, resulting in fewer visits to the clinic and fewer painful injections,” associate professor Green said.
“The biosensor would also be a gamechanger for women living in regional areas, who often have to travel long distances for blood draws.”
As the exact amount of progesterone in interstitial fluid is not well understood, Symex Labs is conducting a world-first clinical study at Monash IVF to establish baseline levels by benchmarking them against concentrations measured in blood samples.
Researchers say their hormone tracking technology also has wider clinical applications beyond the IVF sector.
“Our wearable hormone biosensor has strong potential well beyond fertility care, particularly in PCOS management, perimenopause and menopause symptom management, where continuous hormone insight can replace today’s indirect, symptom-based tracking,” said Symex Labs co-founder Muhammad Umer.
“By integrating directly with consumer health apps, the technology can enable personalised, data-driven management of chronic hormonal conditions and life-stage transitions that currently lack real-time biomarkers.
“For example, if a woman’s oestrogen is going up and down constantly, that’s often a sign that she is getting into that stage, so having access to this health information could help women implement lifestyle changes earlier.”
The research has received A$2.5m in funding from the federal government, the University of Melbourne’s Genesis fund, Monash IVF, RMIT and Breakthrough Victoria.
The first in-human pilot study is expected to get underway within the next 12 months, with commercialisation plans slated for early 2028.
Pregnancy complications may leave women more vulnerable to the long-term heart effects of stress, a recent study suggests.
A study of more than 3,000 women in their first pregnancy found persistently higher stress levels were associated with higher blood pressure after pregnancy, specifically in women who had adverse pregnancy outcomes including preeclampsia, preterm birth, having a baby that was small for gestational age, meaning smaller than expected for that stage of pregnancy, or stillbirth.
Among women who experienced these complications, higher stress levels over time were associated with blood pressure that was 2 mm Hg higher than that of the low-stress group during the years two to seven after delivery.
This was not the case among women who did not experience adverse pregnancy outcomes.
Virginia Nuckols, lead author of the study and a postdoctoral fellow in the University of Delaware’s department of kinesiology and applied physiology, said: “For women who were having babies for the first time and had complications, referred to as adverse pregnancy outcomes, we found that higher stress levels over time were associated with higher blood pressure levels 2-to-7 years after delivery.
“This suggests that women who had pregnancy complications may be more susceptible to the negative effects of stress on their heart health, and taking steps to manage and reduce stress could be important for protecting long-term heart health.”
The researchers analysed records of 3,322 first-time mothers aged 15 to 44 who did not have high blood pressure before pregnancy.
The women were enrolled at 17 medical centres in eight US states, were pregnant with one baby and were having their first child. According to the authors, 66 per cent of participants self-identified as white, 14 per cent as Hispanic and 11 per cent as Black.
Blood pressure and stress levels were measured during the first and third trimesters, and again two to seven years after delivery.
Stress was assessed using the Perceived Stress Scale, a standard questionnaire that asks how often people feel situations are uncontrollable, unpredictable or overwhelming.
Those who experienced moderate to high stress levels were often younger, between 25 and 27 years of age, had higher body mass index, a measure based on height and weight, and lower educational attainment.
The authors said it is not yet clear exactly how higher stress leads to higher blood pressure in women who had pregnancy complications, and that several factors are likely to be involved.
Nuckols added: “Future studies should examine why women with a history of adverse pregnancy outcomes may be more susceptible to stress-driven increases in blood pressure and test whether stress reduction interventions can actually lower cardiovascular risk for these women.”
High blood pressure during pregnancy can have lasting effects on maternal health, including preeclampsia, eclampsia, stroke or kidney problems, according to the American Heart Association’s 2025 guideline for the prevention, detection, evaluation and management of high blood pressure in adults.
Monitoring blood pressure before, during and after pregnancy is crucial to help prevent and reduce the risk of long-term complications.
Laxmi Mehta is chair of the American Heart Association’s Council on Clinical Cardiology and director of preventive cardiology and women’s cardiovascular health at The Ohio State University Wexner Medical Center, and was not involved in the study.
Mehta said;’ “This study highlights the powerful connection between the mind and heart, emphasising the importance of stress management, particularly for those who have experienced adverse pregnancy outcomes.
“For the clinical care team, it reinforces the need to proactively assess and address stress as part of the comprehensive care we provide to our patients.
“Future research on whether targeted interventions to reduce or manage stress has a meaningful impact on long-term cardiovascular outcomes will be important as well.”
AI could help routine mammograms spot heart disease risk in women, as well as breast cancer, researchers have found.
A team from Emory University analysed regular screening scans from more than 123,000 women who had no prior history of cardiovascular disease.
Using an AI programme to quantify calcification and hardening in the arteries, they found women with severe cases had two to three times the risk of developing potentially fatal heart attacks, stroke and heart failure.
“This was true even in younger women under 50, a group often considered low-risk, and held up after accounting for other risk factors like diabetes and smoking,” said Hari Trivedi, Emory associate professor and co-director of the university’s Health Innovation and Translational Informatics lab, who described the research as the largest study of its kind.
“We wanted to test whether AI could use this to identify women at risk of cardiovascular disease at no extra cost or inconvenience.
“”For women, this means a mammogram you’re already having could also provide important information about your heart health, prompting a conversation with your doctor about preventive steps such as cholesterol testing or medication.”
The researchers’ work was published today in the European Heart Journal, from the European Society of Cardiology, which noted that women are largely underdiagnosed and undertreated for cardiovascular disease.
They wrote that the high resolution of routine mammograms could allow for essentially automatic, direct visualisation of the arterial beds within the breasts of nearly all adult women, with calcifications easy to detect and correlated with deposits found in other parts of the body.
The researchers said that, compared with imaging of the heart’s coronary arteries, where blockages narrow and impede the flow of oxygenated blood to the heart muscle, calcifications in breast tissue affect a separate layer of the vessel, resulting in increased artery stiffness, a measure typically linked to long-term hypertension.
They described the finding as an independent predictor of cardiovascular disease and a potentially useful addition to traditional cardiovascular risk factors.
In an accompanying editorial, Lori Daniels, a cardiologist and professor of medicine at the UC San Diego School of Medicine, said that while fewer than 40 per cent of women may know their cholesterol levels, many more are up to date with their breast cancer screening.
“Two-thirds of women aged 50-69 in the European Union reported a mammogram within the prior 2 years, and in the USA, nearly 70 per cent of women aged 45 years and older were up to date with mammography according to American Cancer Society screening guidelines,” Daniels wrote.
“Breast arterial calcification has the potential to reframe this mismatch, leveraging a widely adopted cancer-screening platform to identify cardiovascular risk in women who may not otherwise engage with prevention.”
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