New research has found that protective immune cells in breastfeeding women have been identified as protecting against breast cancer
In the 18th century, doctors noticed that nuns had the highest rates of breast cancer. This was one of the early pieces of evidence that led scientists to suspect that childbearing and breastfeeding could protect against disease.
Recent data have confirmed this centuries-old observation, but the biological reasons behind it have remained unclear. Explanations have often focused on hormonal changes associated with pregnancy, but research… Published Tuesday in Nature Breastfeeding has been found to provide long-term immune protection.
Professor Shireen Lowe, a clinical scientist at the Peter MacCallum Cancer Center in Melbourne, said the most advanced level of the immune system, called the adaptive immune system, includes T cells that react against specific viruses or bacteria – and also against cancer. This response is “one of our most modern therapeutic weapons against cancer.”
Lowe, lead author of the new study, said her team observed that some breast cancers contain large amounts of these specialized immune cells, while others contain very few of these immune cells.
Patients with higher cell counts had better outcomes, especially for one of the most aggressive types: triple-negative breast cancer. These immune cells are also found in healthy breast tissue.
The study sought to investigate why these T cells actually exist, whether they are linked to pregnancy and breastfeeding, and whether they protect against breast cancer formation and growth.
Researchers studied non-cancerous breast tissue from more than 260 women from different populations who underwent breast reduction or surgery to reduce their risk of breast cancer.
They found that those who had children had more of these specialized cells, called CD8⁺ T cells. These cells remain in the breasts for more than 30 years after pregnancy.
Using mouse models, the researchers then cultured cancer cells in the equivalent of breast tissue, and found that they grew less in mice that had given birth to pups and were breastfed, compared to virgin mice.
When they depleted the T cells from mice with pups, they lost protection. This suggests that the T cells were directly responsible for the effect, Lowe said.
The researchers then investigated whether women who breastfed lived longer with triple-negative breast cancer. They looked at studies that involved more than one 1000 patients diagnosed with breast cancer after having children, and breastfeeding history were recorded.
They found that women who breastfed had a better rate of triple-negative breast cancer than those who did not breastfeed. Their tumors also had more immune cells, indicating there was ongoing immune activation and regulation by the body against breast cancer.
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“Key messages to take home [are] “Pregnancy and breastfeeding will leave behind long-lasting protective immune cells in the breast and body,” Lowe said. “These cells help reduce risk and improve defense against breast cancer, especially triple-negative breast cancer, but there are likely other types of cancer as well as diseases.”
Lowe said the study provided an explanation for why breastfeeding is protective, so that it could be used in the future to try to recreate this effect in women who do not have children or are unable to breastfeed.
Understanding the biological mechanism could help develop new vaccines and strategies to mimic this protection, she said.
She stressed that even if a woman breastfeeds, this is not a 100% guarantee that she will not get breast cancer. “The effects are very small for each individual, but the effects are large population-wide.”
Associate Professor Wendy Engman, from the University of Adelaide School of Medicine, said the longer breastfeeding continues, the greater the benefits. She said: For every year of breastfeeding, there is a 4% reduction over the course of a lifetime The mother is at risk of developing breast cancer.
“This study shows that having children and breastfeeding causes long-term changes in immune cells that can help protect the breast from cancer,” she said. “I hope this type of research will lead to new approaches to reducing the risk of breast cancer in women.”