The Protective Role of Breastfeeding in Breast Cancer

Breastfeeding is widely recognized for its role in infant nutrition and development, but it also confers significant health benefits to the mother, particularly in reducing the risk of breast cancer.¹

The act of lactation has been consistently linked to a lower incidence of breast cancer, with epidemiological evidence suggesting a dose-dependent relationship: the longer a woman breastfeeds, the more she may reduce her risk.¹

This protective effect is attributed to hormonal changes that occur during breastfeeding, such as suppressed ovulation, which reduces a woman’s exposure to estrogen.¹

Some of the biological factors suggested to be involved include immunological modulation during breastfeeding, the differentiation of breast tissue, and the exfoliation of potentially damaged cells, which may help in preventing the development of cancer.¹

Emerging evidence suggests that epigenetics may be a key mechanism in the protective role of breastfeeding.² DNA methylation, a process where a methyl group is added to DNA, can silence gene expression.² One gene influenced by this process is FoxA1, which is essential for healthy breast tissue development.²

In breast cancer, FoxA1 is often silenced through hypermethylation.² This can occur due to mutations in the tumor suppressor gene BRCA-1, which helps regulate FoxA1 methylation.² Without proper BRCA-1 function, FoxA1 becomes hypermethylated, increasing breast cancer susceptibility.²

Breastfeeding appears to alter this epigenetic makeup.² Women who breastfeed have been shown to exhibit lower levels of FoxA1 methylation, similar to the protective effect of a functional BRCA-1 gene.² Breastfeeding also has a role in reducing pregnancy-associated plasma protein-A (PAPP-A) overexpression, a common feature in breast cancer.²

The BRCA1-IRIS, a distinct gene product of BRCA-1 that acts as an oncogene, also contributes to breast cancer development, with breastfeeding duration emerging as a key modulator.³ IRIS is crucial for mammary cell growth during pregnancy. Still, its overexpression can fuel aggressive breast cancers, such as triple-negative breast cancer (TNBC).³

Nonetheless, prolonged breastfeeding suppresses IRIS expression and promotes the clearance of potentially cancerous cells.³ Conversely, insufficient breastfeeding may allow IRIS-overexpressing cells to persist, increasing cancer risk.³

This protective effect is further amplified by lactation’s influence on hormone levels and the immune system. Prolactin, stimulated by breastfeeding, suppresses estrogen, a hormone linked to Hormonal Receptor positive breast cancer (HR-positive).¹

Additionally, breast milk delivers a potent mix of modulators, including immune cells, antibodies (e.g., SIgA), and cytokines, potentially bolstering immune surveillance within breast tissue.¹  For example, alpha-lactalbumin and oleic acid found in breast milk have been shown to induce apoptosis in tumor cells.

The cyclical process of lactation and involution, characterized by tissue remodeling and the expression of p53, c-myc, and BCL-xl genes, may further contribute to eliminating precancerous cells and reinforcing genomic integrity.²

Epidemiological studies have consistently shown a correlation between breastfeeding and a reduced risk of breast cancer.

According to a collaborative analysis of data from 47 epidemiological studies conducted in 30 countries, the risk of breast cancer dropped by 4.3% for every 12 months of breastfeeding, in addition to a 7.0% reduction for each birth.⁴

However, another study revealed that parity increases the risk of HR-negative. Still, parous women who breastfed had a lower risk of this type of cancer compared to those who never breastfed.⁵

Notably, the protective effect of breastfeeding seems to be consistent across developed and developing countries⁴. However,  disparities exist among ethnic groups. Black and Hispanic women have higher mortality rates from breast cancer compared to non-Hispanic white women and are less likely to breastfeed.⁶

For example, black women who are particularly affected by aggressive types of cancer also have a lower breastfeeding initiation rate (69.4%) compared to other racial groups.⁷ This has been linked to the fact that approximately 70% of black mothers are the primary economic support of their families, making them return to work shortly after birth.⁷

Breastfeeding has been consistently associated with a decreased risk of breast cancer, with longer durations of lactation providing greater protection. The threshold effect observed in different studies indicates that a significant reduction in breast cancer risk is achieved after a cumulative breastfeeding duration of 6 months.⁸

Bad practices or limitations in breastfeeding can increase the risk of developing breast cancer.⁹ These include early cessation of breastfeeding, not breastfeeding exclusively for the recommended six months⁸, and abrupt involution, which can lead to increased inflammation and ductal hyperplasia, both of which are risk factors for breast cancer.⁹

Does Breastfeeding Reduce Your Risk of Breast Cancer?Play