Breastfeeding reduces the risk of cancer

It has long been known that breastfeeding is associated with a reduction of the risk of certain types of tumor, and indeed the risk decreases further the longer you breastfeed (dose-dependent effect).

The mechanism appears to be linked to:

• lower exposure to estrogen over the course of one's life
• the elimination of breast cells potentially damaged during breastfeeding

According to organizations such as the World Health Organization and the American Cancer Society, breastfeeding is one of the recognized protective factors against breast cancer.

But the most important news is the study comes from a research coordinated by the Australian oncologist Sherene Loi, of the Peter MacCallum Cancer Centre from Melbourne, published in the scientific journal Nature, which provides the first clear biological explanation of how pregnancy and breastfeeding may reduce the risk of breast cancer 

here are the main points of the research:

• The team led by Sherene Loi has demonstrated that pregnancy, breastfeeding and the subsequent return of the breast to its pre-pregnancy state (involution) lead to the accumulation of specialized immune cells (CD8⁺ T cells) in the breast tissue. 
• These immune cells – which normally help the body recognize and destroy potentially harmful cells – they remain in the breast for many years (even decades) after breastfeeding.
• CD8⁺ T cells act as local “sentinels”, ready to react if abnormal cells form that could turn into cancer. 
• In experimental mouse models, the presence of these cells is associated with slower tumor growth and smaller tumors after exposure to cancer cells, but this effect disappears after breastfeeding, and this is considered, in favor of women, one of the benefits of breast milk. 

Australian oncologist Sherene Loi's research examined two groups of women. The first group consisted of 260 healthy women, aged between 20 and 70, who underwent analysis of immune cells in their breast tissue; the second group, consisting of 1.000 women with triple-negative breast cancer, sought to link breastfeeding with T-cell infiltration and clinical outcomes. The conclusion was that the outcomes, for both groups, were significantly better in the breastfeeding group.  

Previously, it was thought that the protection associated with pregnancy and breastfeeding was mainly linked to hormonal changes; however, Loi's research has shown that the immune system plays a key and long-lasting role in protecting against breast cancer. The data indicate that this mechanism may contribute above all to reducing the risk of aggressive forms of breast cancer, such as triple-negative, and also improve outcomes in cases where the disease develops, and therefore represent valuable results for both the prevention and treatment of breast cancer. In summary, Loi and her team have shown that Breastfeeding is not only beneficial for the newborn, but it also involves a lasting modification of the immune system of the mother, with potential preventive effect against breast cancer.

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