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Abortion, Miscarriage, and Breast Cancer Risk 

Introduction 

A woman’s hormone levels normally change throughout her life for a variety of reasons, 

and these hormonal changes can lead to changes in her breasts. Many such hormonal changes 

occur during pregnancy, changes that may influence a woman’s chances of developing breast 

cancer later in life. As a result, over several decades a considerable amount of research has been 

and continues to be conducted to determine whether having an induced abortion, or a miscarriage 

(also known as spontaneous abortion), influences a woman’s chances of developing breast 

cancer later in life. 

Current Knowledge 

In February 2003, the National Cancer Institute (NCI) convened a workshop of over 100 

of the world’s leading experts who study pregnancy and breast cancer risk. Workshop 

participants reviewed existing population-based, clinical, and animal studies on the relationship 

between pregnancy and breast cancer risk, including studies of induced and spontaneous 

abortions. They concluded that having an abortion or miscarriage does not increase a woman’s 

subsequent risk of developing breast cancer. A summary of their findings, titled Summary 

Report: Early Reproductive Events and Breast Cancer Workshop, can be found at 

http://www.cancer.gov/cancerinfo/ere-workshop-report. 
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Related NCI Materials 

• National Cancer Institute Fact Sheet 3.77, Pregnancy and Breast Cancer Risk

http://www.cancer.gov/cancertopics/factsheet/Risk/pregnancy 

• What You Need To Know AboutTM Breast Cancer 

 http://www.cancer.gov/cancerinfo/wyntk/breast 

Background 

The relationship between induced and spontaneous abortion and breast cancer risk has 

been the subject of extensive research beginning in the late 1950s. Until the mid-1990s, the 

evidence was inconsistent. Findings from some studies suggested there was no increase in risk 

of breast cancer among women who had had an abortion, while findings from other studies 

suggested there was an increased risk. Most of these studies, however, were flawed in a number 

of ways that can lead to unreliable results. Only a small number of women were included in 

many of these studies, and for most, the data were collected only after breast cancer had been 

diagnosed, and women’s histories of miscarriage and abortion were based on their “self-report” 

rather than on their medical records. Since then, better-designed studies have been conducted. 

These newer studies examined large numbers of women, collected data before breast cancer was 

found, and gathered medical history information from medical records rather than simply from 

self-reports, thereby generating more reliable findings. The newer studies consistently showed 

no association between induced and spontaneous abortions and breast cancer risk. 
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Ongoing Research Supported by the National Cancer Institute 

Basic, clinical, and population research will continue to be supported which investigate 

the relationship and the mechanisms of how hormones in general and during pregnancy influence 

the development of breast cancer. 

Important Information About Breast Cancer Risk Factors 

At present, the factors known to increase a woman’s chance of developing breast cancer 

include age (a woman’s chances of getting breast cancer increase as she gets older), a family 

history of breast cancer, an early age at first menstrual period, a late age at menopause, a late age 

at the time of birth of her first full-term baby, and certain breast conditions. Obesity is also a risk 

factor for breast cancer in postmenopausal women. More information about breast cancer risk 

factors is found in NCI’s publication What You Need To Know AboutTM Breast Cancer. 

Important Information About Identifying Breast Cancer 

NCI recommends that, beginning in their 40s, women receive mammography screening 

every year or two. Women who have a higher than average risk of breast cancer (for example, 

women with a family history of breast cancer) should seek expert medical advice about whether 

they should be screened before age 40, and how frequently they should be screened. 

# # # 

Sources of National Cancer Institute Information

Cancer Information Service

 Toll-free: 1–800–4–CANCER (1–800–422–6237) 

 TTY (for deaf and hard of hearing callers): 1–800–332–8615 
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NCI Online 

Internet 

Use http://www.cancer.gov to reach the NCI’s Web site. 

LiveHelp 

Cancer Information Specialists offer online assistance through the LiveHelp link on the 

NCI’s Web site. 

 

This fact sheet was reviewed on 5/30/03