Breastfeeding and Reduced Breast Cancer Risk: New Insights
During the 18th century, doctors observed that nuns experienced notably high rates of breast cancer. This sparked early discussions suggesting that pregnancy and breastfeeding might offer some protective benefits against the disease.
Fast forward to today, and modern research has confirmed these historical observations, although the exact biological mechanisms have remained elusive. Previous explanations often revolved around hormonal changes linked to pregnancy. However, a recent study published in Nature has shed light on how breastfeeding may provide lasting immune protection.
According to Prof. Sherene Loi, a clinician scientist at the Peter MacCallum Cancer Centre in Melbourne, the adaptive immune system—complete with T-cells—plays a crucial role in combating specific infections and, intriguingly, cancer as well. This aspect of the immune response is considered “one of our very modern therapeutic weapons against cancer.”
Loi, leading the study, noted that some breast cancer cases exhibited a higher presence of these specialized immune cells compared to others. Those with increased T-cell counts appeared to have better outcomes, particularly in cases of aggressive triple-negative breast cancer. Remarkably, similar immune cells were even detected in healthy breast tissue.
The research aimed to explore the presence of T-cells, investigating whether they were connected to pregnancy and breastfeeding and if they could act against the development and growth of breast cancer.
The team analyzed noncancerous breast tissue from over 260 women who underwent breast reduction or surgeries to mitigate breast cancer risk. The findings revealed that mothers had more CD8⁺ T-cells, which lingered in breast tissues for over three decades post-pregnancy.
In experimental models using mice, researchers injected cancerous cells into breast tissue equivalents and discovered that those who had given birth and breastfed showed slower tumor growth compared to virgin mice. Once they removed the T-cells from the mother mice, the protective effect diminished, suggesting that these cells were essential in combating the disease.
The study also examined whether breastfeeding influenced survival rates among women with triple-negative breast cancer. Analyzing over 1,000 patients, researchers found that those who breastfed fared better than those who did not. Their tumors contained more immune cells, hinting at sustained immune activation against the cancer.
“The main takeaway,” Loi stated, “is that pregnancy and breastfeeding leave behind durable immune cells in the breast and body, which help lower risk and bolster defenses against breast cancer—especially triple-negative, possibly extending to other cancers as well.”
She added that the research offers insight into breastfeeding’s protective qualities, which could inform approaches for women unable to conceive or nurse in the future. Understanding these biological mechanisms might pave the way for vaccine development and new protective strategies.
However, Loi is careful to note that breastfeeding doesn’t guarantee immunity against breast cancer. “The effects are relatively small for each individual, but they can be significant on a population level.”
Associate Prof. Wendy Ingman from the University of Adelaide highlighted that longer breastfeeding durations yield greater protective benefits. For every year of breastfeeding, the risk of breast cancer may decrease by around 4% for mothers.
“This study underscores that having children and breastfeeding induces lasting immune changes that might shield the breast from cancer,” Ingman remarked. “I’m optimistic that this research will inspire new methods to lower breast cancer risks for women.”
