Is breast cancer more likely to progress during pregnancy?

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Breast Cancer Progression During Pregnancy: An Analysis

Introduction to Breast Cancer and Pregnancy

Breast cancer during pregnancy, also known as pregnancy-associated breast cancer (PABC), is a rare but increasingly observed condition due to the trend of delayed childbearing. This article synthesizes current research to address whether breast cancer is more likely to progress during pregnancy.

Increased Risk of Breast Cancer Post-Pregnancy

Several studies indicate a transient increase in the risk of breast cancer following childbirth. A comprehensive case-control study in Sweden found that uniparous women (those with one child) had a higher risk of developing breast cancer for up to 15 years post-childbirth compared to nulliparous women (those with no children). This risk was particularly pronounced in women who had their first child at an older age. However, the risk decreased in the long term, suggesting a dual effect of pregnancy on breast cancer risk.

Aggressiveness and Prognosis of Breast Cancer During Pregnancy

Breast cancer diagnosed during pregnancy is often more aggressive and is frequently characterized by a triple-negative phenotype, which is associated with poorer prognosis and outcomes. A meta-analysis of 41 studies revealed that women diagnosed with breast cancer during pregnancy or up to five years postpartum had a significantly higher risk of death and disease progression compared to non-pregnant controls. This increased risk was most notable in those diagnosed postpartum.

Obstetric and Perinatal Complications

Women diagnosed with breast cancer during pregnancy face higher risks of obstetric and perinatal complications. A population-based study in Sweden reported increased risks of preterm birth, low birth weight, and other related adverse outcomes in these women. These risks were particularly elevated when the cancer was diagnosed in the second trimester.

Mechanisms Behind Poor Prognosis

The poor prognosis of PABC may be attributed to the mammary microenvironment during and after pregnancy. The remodelling of the mammary gland to its pre-pregnant state involves pro-inflammatory and wound-healing mechanisms that may promote tumor-cell dissemination. This hypothesis suggests that the physiological changes during pregnancy create a tumor-promoting environment.

Short-Term Increase in Risk

Data from hospital-based case-control studies in Italy support the notion of a short-term increase in breast cancer risk following full-term pregnancy. Women who had given birth within three years prior had a significantly higher relative risk of breast cancer compared to those whose last birth was ten or more years before. This transient increase in risk is thought to contrast with the long-term protective effects of early childbirth.

Immune Microenvironment and Risk Profiles

The tumor immune microenvironment in PABC differs from that in early-onset breast cancer in non-pregnant women. PABC is characterized by specific patterns of tumor-infiltrating lymphocytes (TILs) and immune markers, which are associated with higher risks of relapse and disease-related death. This unique immune landscape underscores the need for tailored therapeutic approaches.

Conclusion

In summary, breast cancer diagnosed during pregnancy is associated with a higher risk of progression and poorer prognosis. The transient increase in risk post-childbirth, the aggressive nature of PABC, and the unique tumor microenvironment all contribute to this heightened risk. Understanding these factors is crucial for developing effective management strategies for pregnant women with breast cancer.