In the 18th century, doctors noticed that nuns had some of the highest rates of breast cancer. This was one of the first signs that led scientists to suspect that pregnancy and breastfeeding could protect against the disease.
Modern data have confirmed centuries-old observations, but the biological reasons for this phenomenon remain unclear. Explanations often focus on hormonal changes associated with pregnancy, but research published Tuesday in the journal Nature found that breastfeeding provides long-lasting immune protection.
Professor Sharene Loy, a clinical scientist at the Peter MacCallum Cancer Center in Melbourne, said the most complex level of the immune system, called the adaptive immune system, included T cells that respond to certain viruses or bacteria, as well as cancer. This answer “One of our most advanced cancer therapeutics”.
Loy, senior author of the new study, said her team noticed that some breast cancers contained large numbers of these specialized immune cells, while others had very few.
Patients who had more cells had better outcomes, especially for one of the most aggressive types: triple negative breast cancer. These immune cells were also found in healthy breast tissue.
The goal of the study was to find out why these T cells already exist, whether they are associated with pregnancy and breastfeeding, and whether they protect against the formation and growth of breast cancer.
Researchers studied noncancerous breast tissue from more than 260 women from different populations who had breast reduction or surgery to reduce their risk of developing breast cancer.
They found that those who had children had more of these specialized cells called CD8⁺ T cells. These cells remained in the breasts for more than 30 years after pregnancy.
Using mouse models, the researchers then implanted the cancer cells into the equivalent of breast tissue and found that in mice that had puppies and were breastfed, they grew less than in virgin mice.
When they depleted the T cells in the mice with their pups, they lost protection. This suggests that T cells are directly responsible for the effect, Loy said.
The researchers then examined whether breastfeeding women with triple-negative breast cancer lived longer. They reviewed studies that included more than 1000 breast cancer patients who were diagnosed with cancer after having children and had a record of breastfeeding history.
They found that women who breastfed fared better against triple negative breast cancer than those who did not. Their tumors also had more immune cells, suggesting that immune activation and regulation against breast cancer continues in the body.
“Main conclusions [are] that pregnancy and breastfeeding leave behind long-lived protective immune cells in the breast and body, and these cells help reduce the risk and improve protection against breast cancer, especially triple negative breast cancer, but possibly other cancers and diseases as well,” Loy said.
Loy said the study provided an explanation for why breastfeeding is protective and that it could be used in the future to try to recreate that effect in women who do not have children or are unable to breastfeed.
Understanding the biological mechanism could help develop vaccines and new strategies that mimic this protection, she said.
She emphasized that even if women breastfeed, this is not a 100% guarantee that they will not get breast cancer. “The effects are actually quite small for each individual, but on a population scale the effects are huge.”
Associate Professor Wendy Ingman, from the University of Adelaide Medical School, says the longer the duration of breastfeeding, the greater the benefits. She said: For every year of breastfeeding, life expectancy decreases by 4%. at risk of maternal breast cancer.
“This study shows that childbirth and breastfeeding causes long-term changes in immune cells that may help protect breasts from cancer,” she said. “I hope that this type of research will lead to new approaches to reducing the risk of breast cancer in women.”
