CancerMail from the National Cancer Institute

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 *                                CANCER FACTS                                *
 *                          National Cancer Institute                         *
 *                        National Institutes of Health                       *
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Abortion and Breast Cancer


                   
The relationship between abortion and breast cancer has been the
subject of extensive research. The current body of scientific evidence
suggests that women who have had either induced or spontaneous
abortions have the same risk as other women for developing breast
cancer. Until the mid-1990s, results from studies of breast cancer and
induced or spontaneous abortion were inconsistent. Some investigators
reported an increase in risk, typically from interview studies of
several hundred breast cancer patients compared to other women. Other
studies found no evidence of increased risk.
   
Recent large studies, particularly cohort studies, generally show no
association between breast cancer risk and previously recorded
spontaneous or induced abortions. In a large-scale epidemiologic study
reported in The New England Journal of Medicine in 1997, researchers
compared data from Danish health registries that included 1.5 million
women and more than 10,000 cases of breast cancer. The registry data
on abortions was collected before the diagnosis of breast cancer
was made. After adjusting the data for several established breast
cancer risk factors, the authors found that induced abortions have
no overall effect on the risk of breast cancer. The strengths of this
study include its large size, the ability to account for breast cancer
risk factors that may differ between women who have had abortions and
those who have not, and the availability of information on abortion
from registries rather than having to rely on a womans self-reported
history of abortion.
   
In 2000 and 2001, additional findings were reported from studies that
collected data on abortion history before the breast cancers occurred.
These studies showed no increased breast cancer risk in women who had
induced abortions. In three of the studies, information on abortion
was based on medical records rather than on the womans self-report; in
another study, interview data was collected before any breast cancer
diagnosis. The studies were conducted in different populations of
women, and varied in size and the extent of details on established
breast cancer risk factors.
   
Most of the early studies necessarily relied on self-reports of
induced abortion, which have been shown to differ between breast
cancer patients and other women. Other problems with these studies
included small numbers of women, questions of comparability between
women with breast cancer and those without, inability to separate
induced from spontaneous abortions, and incomplete knowledge of other
breast cancer risk factors that may have been related to a womans
history of abortion.
   
Even though it appears that there is no overall association between
spontaneous or induced abortion and breast cancer risk, it is possible
that an increased or decreased risk could exist in small subgroups of
women. For example, the large Danish study found a slightly lower
breast cancer risk in women with abortions occurring before 7 weeks
gestation, and a slightly higher risk in women who had abortions at 7
or more weeks. The National Cancer Institute is currently funding at
least six other studies examining complete pregnancy history,
including induced and spontaneous abortion, in relation to the risk of
breast cancer.
   
Well-established breast cancer risk factors include age, a family
history of breast cancer, an early age at menarche, a late age at
menopause, a late age at the time of the first birth of a full-term
baby, alcohol consumption, and certain breast conditions. Obesity is a
risk factor for breast cancer in postmenopausal women.
   
References: 
   
Goldacre MJ, Kurina LM, Seagroatt V, Yeates D. Abortion and breast
cancer: A case-control record linkage study. Journal of Epidemiology
and Community Health 2001; 55:3367.
   
Lazovich D, Thompson JA, Mink PJ, Sellers TA, Anderson KE. Induced
abortion and breast cancer risk. Epidemiology 2000; 11:7680.
   
Melbye M, Wohlfahrt M, Olsen JH, et al. Induced abortion and the risk
of breast cancer. The New England Journal of Medicine 1997; 336:8185.
   
Michels KB, Willett WC. Does induced or spontaneous abortion affect
the risk of breast cancer? Epidemiology 1996; 7:521528.
   
Newcomb PA, Mandelson MT. A record-based evaluation of induced
abortion and breast cancer risk (United States). Cancer Causes and
Control 2000; 11:777781.
   
Rookus, MA, van Leeuwen, FE. Induced abortion and risk for breast
cancer: Reporting (recall) bias in a Dutch case-control study. Journal
of the National Cancer Institute 1996; 88:17591764.
   
Tang M-T C, Weiss NS, Malone KE. Induced abortion in relation to
breast cancer among parous women: A birth certificate registry study.
Epidemiology 2000; 11:177180.
   

This fact sheet was reviewed on 3/06/02

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Date Last Modified: 03/2002

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