Breastfeeding linked to lower breast cancer risk

Australian-led research has offered new insight into how childbirth and breastfeeding can lower a woman’s long-term risk of breast cancer.
 
The study, published this week in the journal Nature, sets out a biological explanation for the protective effect of childbearing and breastfeeding and how it can have a lasting impact on a woman’s immune system.
 
Professor Sherene Loi, a medical oncologist at the Peter MacCallum Cancer Centre, led and co-wrote the research, saying it could offer greater understanding of breast cancer prevention and treatment.
 
‘We found that women who have breastfed have more specialised immune cells, called CD8⁺ T cells, that “live” in the breast tissue for decades after childbirth,’ she said.
 
‘These cells act like local guards, ready to attack abnormal cells that might turn into cancer.
 
‘This protection may have evolved to defend mothers during the vulnerable post-pregnancy period, but today it also lowers breast cancer risk, especially the aggressive type called triple-negative breast cancer.’
 
According to the research, ‘a full cycle’ of pregnancy, breastfeeding and breast recovery prompts the T cells to gather in the breast.
 
‘When breast cancer cells were introduced, the models with this reproductive history were far better at slowing or stopping tumour growth but only if T cells were present,’ Professor Loi said.
 
‘We also studied data from over 1000 breast cancer patients and found women who breastfed had tumours with higher numbers of these protective T cells and, in some groups, they lived longer after diagnosis of breast cancer.’
 
The researchers also considered 260 healthy women who had undergone preventative mastectomies or breast reductions, comparing the T-cell count in removed breast tissue.
 
They found women who had children had more T cells and that those cells were long-lived – sometimes lasting up to 50 years after pregnancy.
 
Researchers also used mice models to consider whether pregnancy and breastfeeding protect against breast cancer.
 
While breastfeeding is already known for cutting the risk of breast cancer, the reasons behind it have not been clear.
 
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