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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.”
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pain conditions
Endometriosis documentary profiles stars including Marilyn Monroe and Amy Schumer

A non-profit has launched an endometriosis documentary featuring Amy Schumer and Marilyn Monroe as it pushes for changes in how the condition is treated and understood.
The Endometriosis Collective has launched to change how endometriosis is researched, treated and understood, starting with a documentary featuring stories from people including Amy Schumer and Marilyn Monroe.
The feature-length documentary, “End of the Cycle”, will premiere in New York on Tuesday, and The Endometriosis Collective is making the film free to stream online.
Schumer, a comedian, writer and actor, has previously spoken of how endometriosis left her “on the floor in pain, vomiting from the pain, the pain that nobody can see.”
Schumer is one of several celebrities featured in the documentary. Other contributors include dancer Julianne Hough, Olympic medallist Brittany Brown and actors Janel Parrish and Folake Olowofoyeku.
The Endometriosis Collective timed the documentary premiere to coincide with the 100th anniversary of Marilyn Monroe’s birth.
Monroe, who died in 1962, starred in films such as “Some Like It Hot” and “Gentlemen Prefer Blondes.”
According to a biography published in 1985, Monroe’s endometriosis was so severe that it destroyed her marriages, her wish for children, her career and ultimately her life.
The Endometriosis Collective said the documentary shares newly uncovered information about Monroe’s experience with endometriosis.
The non-profit said the information connects Monroe’s story to the experiences of women across generations, highlighting how far awareness, research and care still have to go.
A representative of the Marilyn Monroe Estate said: “By sharing this part of her story through ‘End of the Cycle,’ we hope to honour her legacy in a way that brings visibility to endometriosis, encourages more open dialogue and helps inspire the research needed to create change.”
As part of the premiere, The Endometriosis Collective is holding a panel discussion.
Schumer, Brown and Olowofoyeku, the documentary’s co-directors Sammy Jaye and Soraya Simi, and medical experts are due to be part of the premiere.
AbbVie’s Orilissa and Sumitomo Pharma’s Myfembree are among the approved drugs for endometriosis pain.
Hough, one of the participants in the documentary, starred in an Orilissa campaign in 2017.
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