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Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries

Beral, Valerie; Bull, Diana; Doll, Richard; Peto, Richard; Reeves, Gillian; Möller, Torgil LU ; Olsson, Håkan LU ; Ranstam, J and Collaborative Group on Hormonal Factors in Breast Cancer, and the (2004) In The Lancet 363(9414). p.1007-1016
Abstract
BACKGROUND: The Collaborative Group on Hormonal Factors in Breast Cancer has brought together the worldwide epidemiological evidence on the possible relation between breast cancer and previous spontaneous and induced abortions. METHODS: Data on individual women from 53 studies undertaken in 16 countries with liberal abortion laws were checked and analysed centrally. Relative risks of breast cancer--comparing the effects of having had a pregnancy that ended as an abortion with those of never having had that pregnancy--were calculated, stratified by study, age at diagnosis, parity, and age at first birth. Because the extent of under-reporting of past induced abortions might be influenced by whether or not women had been diagnosed with breast... (More)
BACKGROUND: The Collaborative Group on Hormonal Factors in Breast Cancer has brought together the worldwide epidemiological evidence on the possible relation between breast cancer and previous spontaneous and induced abortions. METHODS: Data on individual women from 53 studies undertaken in 16 countries with liberal abortion laws were checked and analysed centrally. Relative risks of breast cancer--comparing the effects of having had a pregnancy that ended as an abortion with those of never having had that pregnancy--were calculated, stratified by study, age at diagnosis, parity, and age at first birth. Because the extent of under-reporting of past induced abortions might be influenced by whether or not women had been diagnosed with breast cancer, results of the studies--including a total of 44000 women with breast cancer--that used prospective information on abortion (ie, information that had been recorded before the diagnosis of breast cancer) were considered separately from results of the studies--including 39000 women with the disease--that used retrospective information (recorded after the diagnosis of breast cancer). FINDINGS: The overall relative risk of breast cancer, comparing women with a prospective record of having had one or more pregnancies that ended as a spontaneous abortion versus women with no such record, was 0.98 (95% CI 0.92-1.04, p=0.5). The corresponding relative risk for induced abortion was 0.93 (0.89-0.96, p=0.0002). Among women with a prospective record of having had a spontaneous or an induced abortion, the risk of breast cancer did not differ significantly according to the number or timing of either type of abortion. Published results on induced abortion from the few studies with prospectively recorded information that were not available for inclusion here are consistent with these findings. Overall results for induced abortion differed substantially between studies with prospective and those with retrospective information on abortion (test for heterogeneity between relative risks: chi2(1) =33.1, p<0.0001). INTERPRETATION: Pregnancies that end as a spontaneous or induced abortion do not increase a woman's risk of developing breast cancer. Collectively, the studies of breast cancer with retrospective recording of induced abortion yielded misleading results, possibly because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Lancet
volume
363
issue
9414
pages
1007 - 1016
publisher
Elsevier Limited
external identifiers
  • scopus:1642634952
  • pmid:15051280
ISSN
1474-547X
DOI
10.1016/S0140-6736(04)15835-2
language
English
LU publication?
yes
id
9a02f958-14e0-46c8-9daf-e6be83b396ca (old id 1129655)
date added to LUP
2008-08-15 15:54:57
date last changed
2017-08-27 04:00:06
@article{9a02f958-14e0-46c8-9daf-e6be83b396ca,
  abstract     = {BACKGROUND: The Collaborative Group on Hormonal Factors in Breast Cancer has brought together the worldwide epidemiological evidence on the possible relation between breast cancer and previous spontaneous and induced abortions. METHODS: Data on individual women from 53 studies undertaken in 16 countries with liberal abortion laws were checked and analysed centrally. Relative risks of breast cancer--comparing the effects of having had a pregnancy that ended as an abortion with those of never having had that pregnancy--were calculated, stratified by study, age at diagnosis, parity, and age at first birth. Because the extent of under-reporting of past induced abortions might be influenced by whether or not women had been diagnosed with breast cancer, results of the studies--including a total of 44000 women with breast cancer--that used prospective information on abortion (ie, information that had been recorded before the diagnosis of breast cancer) were considered separately from results of the studies--including 39000 women with the disease--that used retrospective information (recorded after the diagnosis of breast cancer). FINDINGS: The overall relative risk of breast cancer, comparing women with a prospective record of having had one or more pregnancies that ended as a spontaneous abortion versus women with no such record, was 0.98 (95% CI 0.92-1.04, p=0.5). The corresponding relative risk for induced abortion was 0.93 (0.89-0.96, p=0.0002). Among women with a prospective record of having had a spontaneous or an induced abortion, the risk of breast cancer did not differ significantly according to the number or timing of either type of abortion. Published results on induced abortion from the few studies with prospectively recorded information that were not available for inclusion here are consistent with these findings. Overall results for induced abortion differed substantially between studies with prospective and those with retrospective information on abortion (test for heterogeneity between relative risks: chi2(1) =33.1, p&lt;0.0001). INTERPRETATION: Pregnancies that end as a spontaneous or induced abortion do not increase a woman's risk of developing breast cancer. Collectively, the studies of breast cancer with retrospective recording of induced abortion yielded misleading results, possibly because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions.},
  author       = {Beral, Valerie and Bull, Diana and Doll, Richard and Peto, Richard and Reeves, Gillian and Möller, Torgil and Olsson, Håkan and Ranstam, J and Collaborative Group on Hormonal Factors in Breast Cancer, and the},
  issn         = {1474-547X},
  language     = {eng},
  number       = {9414},
  pages        = {1007--1016},
  publisher    = {Elsevier Limited},
  series       = {The Lancet},
  title        = {Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries},
  url          = {http://dx.doi.org/10.1016/S0140-6736(04)15835-2},
  volume       = {363},
  year         = {2004},
}