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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.

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<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.

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  • Authors

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    Source

    Lancet (London, England) 363:9414 2004 Mar 27 pg 1007-16

    MeSH

    Abortion, Induced
    Abortion, Spontaneous
    Adolescent
    Adult
    Breast Neoplasms
    Comorbidity
    Female
    Global Health
    Humans
    International Cooperation
    Middle Aged
    Parity
    Pregnancy
    Prospective Studies
    Retrospective Studies
    Risk

    Pub Type(s)

    Comparative Study
    Journal Article
    Multicenter Study
    Review

    Language

    eng

    PubMed ID

    15051280

    Citation

    Beral, Valerie, et al. "Breast Cancer and Abortion: Collaborative Reanalysis of Data From 53 Epidemiological Studies, Including 83?000 Women With Breast Cancer From 16 Countries." Lancet (London, England), vol. 363, no. 9414, 2004, pp. 1007-16.
    Beral V, Bull D, Doll R, et al. Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries. Lancet. 2004;363(9414):1007-16.
    Beral, V., Bull, D., Doll, R., Peto, R., & Reeves, G. (2004). Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries. Lancet (London, England), 363(9414), pp. 1007-16.
    Beral V, et al. Breast Cancer and Abortion: Collaborative Reanalysis of Data From 53 Epidemiological Studies, Including 83?000 Women With Breast Cancer From 16 Countries. Lancet. 2004 Mar 27;363(9414):1007-16. PubMed PMID: 15051280.
    * Article titles in AMA citation format should be in sentence-case
    TY - JOUR T1 - Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries. AU - Beral,Valerie, AU - Bull,Diana, AU - Doll,Richard, AU - Peto,Richard, AU - Reeves,Gillian, AU - ,, PY - 2004/3/31/pubmed PY - 2004/4/30/medline PY - 2004/3/31/entrez SP - 1007 EP - 16 JF - Lancet (London, England) JO - Lancet VL - 363 IS - 9414 N2 - 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. SN - 1474-547X UR - https://www.unboundmedicine.com/medline/citation/15051280/full_citation L2 - https://linkinghub.elsevier.com/retrieve/pii/S0140673604158352 DB - PRIME DP - Unbound Medicine ER -