Although we have known for a long time that breastfeeding is associated with a reduction in the risk of breast cancer – the most diagnosed in France in 2023 and the second in the world in 2022 – the mechanisms underlying this protection have until now remained unclear. Australian researchers from the Peter MacCallum Cancer Center in the state of Victoria have just identified a promising avenue: women who have breastfed may retain immune cells in their breast tissue capable of detecting and slowing the growth of cancer cells.
According to previous studies, the risk of breast cancer would decrease by approximately 4.3% for each year of breastfeeding, with a more marked protective effect among older mothers. As reported by the media New Scientist, the team of professor and oncologist Sherene Loi analyzed samples of breast tissue from 260 women aged 20 to 70, some of whom had breastfed and others not. None of them had ever had breast cancer before.
It has been found that women who have breastfed have a large quantity of specialized immune cells, called “CD8 + T lymphocytes”, protecting the body against any type of viral or bacterial infection. The researchers highlighted the fact that these lymphocytes remained present in the body up to fifty years after childbirth and acted as guardians of immunity, capable of recognizing and attacking possible malignant cells.
The team continued the experiment on a batch of mice. Only those who had completed a full cycle of pregnancy and breastfeeding had an accumulation of these T cells in their mammary glands, unlike mice that had never been pregnant.
Increased life expectancy
When they were implanted with the cells of a particularly aggressive breast cancer, known as “triple negative”, the growth of the tumors was found to be much slower in the lactating mice. In contrast, as soon as the T cells were removed from the mammary glands, the tumors grew rapidly.
To confirm their observations, the researchers relied on clinical data from more than a thousand women with post-pregnancy triple negative breast cancer. Thus, those who had breastfed had tumors with a higher density of CD8 + T cells, a sign of an effective immune response.
After adjusting for other risk factors such as age, women who breastfed had a significantly longer life expectancy. Indeed, these cells accumulate in the breast during breastfeeding to prevent infections likely to cause inflammation of these cells, like mastitis, a common infection in breastfeeding women.
For professor and biologist Daniel Gray of the Walter and Eliza Hall Medical Research Institute in Victoria, the study opens the way to new research into the functioning of the immune memory of CD8 + T cells.
However, as Sherene Loi points out, some women are not necessarily able to breastfeed and breastfeeding obviously does not guarantee the absence of cancer.
