Breastfeeding promotes an increase in immune cells capable of neutralizing any tumor threats: the benefits can last decades.
Breastfeeding encourages massive production of immune cells and their migration to the breast, where they are destined to stay for years, even decades. This would be, according to a study published in Naturethe mechanism underlying the protective effect that breastfeeding has on breast cancer: past studies have calculated that, for every year of breastfeeding, the risk of getting this form of cancer is reduced by 4.3%.
The recruitment of specialized lymphocytes
The changes that the breast undergoes during pregnancy and after giving birth, first to prepare to secrete milk and then, after weaning, to stop producing milk again, cause a significant number of cytotoxic T lymphocytes (CD8+ T) to migrate “in place”, cells capable of infiltrating tumors and attacking them, destroying the malignant cells. Other mechanisms of an immune nature, triggered by the proteins in breast milk, by the material present in the mouth of newborns or by the protection of the breast from mastitis (an inflammation of the mammary gland) also attract the same type of lymphocytes.
For Sherene Loi, oncologist at the Peter MacCullum Cancer Center in Victoria, Australia, in women who have breastfed these cells can live for decades in the breast tissue, where “they act as local guards, ready to attack abnormal cells that could turn into cancer.”
A research in three parts
Loi and colleagues first compared the number of this type of lymphocytes in the breast tissue of 260 healthy women, with or without children, who had undergone either breast reduction surgery or preventive mastectomy (for a moderate to high risk of breast cancer). An increased number of cytotoxic T lymphocytes was observed in the tissues of women who had had children and breastfed, and persisted for several decades.
In a second experiment, scientists introduced cells from an aggressive form of breast cancer into the mammary tissue of female mice that had completed one birth and a full nursing and weaning cycle, or had never given birth, or had been unable to breastfeed because they were separated from their pups after giving birth. In the former, the tumors grew less and appeared to be attacked by more cytotoxic T cells. When these “immune gatekeepers” were removed, the tumors grew more rapidly.
Finally, the team analyzed clinical data from more than a thousand women who had had triple-negative breast cancer (a subtype of breast cancer lacking the three main molecular targets for which targeted treatments exist) and at least one full pregnancy.
In women who reported breastfeeding, tumors had a higher density of cytotoxic T lymphocytes. All other variables being equal, these patients had a longer survival.
Extend benefits
The study leaves many open questions, for example which proteins are targeted by these lymphocytes, how they persist for years or what their relationship is with tumors that – like breast cancer – are sensitive to hormones. The answers will be important to develop universal treatments for the prevention of breast cancer, even in women who, by choice, impossibility or because they have not had a pregnancy, have not breastfed. “We would like to understand what T cells react to, because then we can perhaps create strategies that imitate this same effect” explains Loi.
