Breastfeeding boosts immune cells that protect against breast cancer

"Breastfeeding is known to reduce the risk of breast cancer, but the mechanism underlying this protection has been unclear. During pregnancy and postpartum, the human breast significantly remodels itself to create a supply of nutritious milk to help a baby's organs, brain and bones to grow. After weaning, the breast goes through a process called involution, changing back. During this process, new cells are created and older, damaged cells are cleared out."

"This biological redesign is also "a main trigger" for the recruitment of specialized immune cells to the breast, called CD8+ T cells, says study co-author Sherene Loi. Other immune challenges, including milk proteins, any foreign material coming from the baby, mastitis and viruses, also bring T cells to the breast tissue, says Loi, a medical oncologist at the Peter MacCallum Cancer Centre in Melbourne, Australia."

"Loi and her colleagues' research had three parts. First, they looked at a diverse population of 260 healthy women who had undergone preventative mastectomies or breast reductions - some of whom had a normal risk of breast cancer, others an elevated risk - and compared the T-cell count in the removed breast tissue of women with and without children. Women who had had children had more T cells and those cells were long-lived, persisting for up to 50 years after pregnancy."

Pregnancy and breastfeeding remodel the human breast through lactation and involution, creating conditions that recruit specialized CD8+ T cells. Immune triggers during this period include milk proteins, foreign material from the baby, mastitis and viruses, all of which bring T cells to breast tissue. Analysis of breast tissue from 260 women showed higher T-cell counts in parous women, with those cells persisting for up to 50 years after pregnancy. Mouse experiments comparing nulliparous, early-weaned and fully lactating mice linked full lactation and involution with reduced tumour growth following cancer cell introduction.

Read at Nature