Beral Valerie, Bull Diana, Doll Richard, Peto Richard, Reeves Gillian
Lancet. 2004 Mar 27;363(9414):1007-16. doi: 10.1016/S0140-6736(04)15835-2.
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.
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).
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).
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.
乳腺癌激素因素协作组汇总了全球范围内关于乳腺癌与既往自然流产和人工流产之间可能存在的关系的流行病学证据。
对在16个拥有宽松堕胎法律的国家开展的53项研究中的个体女性数据进行集中核查和分析。计算乳腺癌的相对风险——比较曾有过以流产告终的妊娠与从未有过该妊娠的影响——并按研究、诊断时年龄、产次和初产年龄进行分层。由于既往人工流产漏报的程度可能受女性是否被诊断患有乳腺癌的影响，因此将使用堕胎前瞻性信息（即乳腺癌诊断前记录的信息）的研究结果（共纳入44000例乳腺癌女性）与使用回顾性信息（乳腺癌诊断后记录）的研究结果（共纳入39000例该疾病女性）分开考虑。
比较有过一次或多次以自然流产告终的妊娠的前瞻性记录的女性与无此类记录的女性，乳腺癌的总体相对风险为0.98（95%置信区间0.92 - 1.04，p = 0.5）。人工流产的相应相对风险为0.93（0.89 - 0.96，p = 0.0002）。在有自然流产或人工流产前瞻性记录的女性中，乳腺癌风险在两种流产类型的数量或时间方面无显著差异。此处未纳入的少数有前瞻性记录信息的人工流产研究的已发表结果与这些发现一致。人工流产的总体结果在使用堕胎前瞻性信息的研究和使用回顾性信息的研究之间存在显著差异（相对风险异质性检验：卡方(1)=33.1，p<0.0001）。
以自然流产或人工流产告终的妊娠不会增加女性患乳腺癌的风险。总体而言，对人工流产进行回顾性记录的乳腺癌研究得出了误导性结果，可能是因为患乳腺癌的女性比其他女性平均更有可能披露既往人工流产情况。
