18 - Pregnancy and breast cancer

Summary

Introduction

Pregnancy and associated factors are known to modify breast cancer risk. In addition, pregnancy-associated breast cancer (PABC) — defined as breast cancer that is diagnosed during a pregnancy or within 1 year postpartum — is a clinically challenging situation for the patients, their families and their physicians.

This review attempts to identify how pregnancy and lactation modify breast cancer risk, highlight what can be regarded as state of the art in the diagnosis and treatment of PABC, and consider the issue of preserving fertility during the treatment of breast cancer.

Pregnancy-associated factors and breast cancer risk

Intrauterine factors and breast cancer risk

It has recently become clear that the stage for carcinogenesis might be set as early as the perinatal period. A systematic search for studies that assessed association between perinatal factors and risk of breast cancer was performed by Michels and Xue. Their findings are summarised in this section.

Birth weight

The majority of the nearly 30 studies on this topic identified a positive link between birth weight and premenopausal, but less commonly postmenopausal, breast cancer. The relative risk (RR) estimate for breast cancer comparing women with high birth weight with women with low birth weight combining all studies was 1.15 (95% CI 1.09—1.21). The mechanisms underlying this association probably include elevated levels of growth factors that may increase the number of susceptible stem cells in the mammary gland or initiate tumours through DNA mutations.