Newcomb P A, Storer B E, Longnecker M P, Mittendorf R, Greenberg E R, Clapp R W, Burke K P, Willett W C, MacMahon B
University of Wisconsin Comprehensive Cancer Center, Madison 53706.
N Engl J Med. 1994 Jan 13;330(2):81-7. doi: 10.1056/NEJM199401133300201.
The evidence of an association of lactation with a reduction in the risk of breast cancer among women has been limited and inconsistent. The effect of lactation appears to be confined to premenopausal women with a history of long lactation, but most studies of this relation have been limited in statistical power. We conducted a multicenter, population-based, case-control study with a sample large enough for us to describe more precisely the association between lactation and the risk of breast cancer.
Patients less than 75 years old who had breast cancer were identified from statewide tumor registries in Wisconsin, Massachusetts, Maine, and New Hampshire. Controls were randomly selected from lists of licensed drivers if the case subjects were less than 65 years old, and from lists of Medicare beneficiaries if they were 65 through 74 years old. Information on lactation, reproductive history, and family and medical history was obtained by means of telephone interviews. After the exclusion of nulliparous women, 5878 case subjects and 8216 controls remained for analysis.
After adjustment for parity, age at first delivery, and other risk factors for breast cancer, lactation was associated with a slight reduction in the risk of breast cancer among premenopausal women, as compared with the risk among women who were parous but had never lactated (relative risk, 0.78; 95 percent confidence interval, 0.66 to 0.91); the relative risk of breast cancer among postmenopausal women who had lactated, as compared with those who had not, was 1.04 (95 percent confidence interval, 0.95 to 1.14). With an increasing cumulative duration of lactation, there was a decreasing risk of breast cancer among premenopausal women (P for trend < 0.001) but not among postmenopausal, parous women (P for trend = 0.51). A younger age at first lactation was significantly associated with a reduction in the risk of premenopausal breast cancer (P for trend = 0.003). As compared with parous women who did not lactate, the relative risk of breast cancer among women who first lactated at less than 20 years of age and breast-fed their infants for a total of six months was 0.54 (95 percent confidence interval, 0.36 to 0.82).
There is a reduction in the risk of breast cancer among premenopausal women who have lactated. No reduction in the risk of breast cancer occurred among postmenopausal women with a history of lactation.
关于哺乳期与女性患乳腺癌风险降低之间存在关联的证据有限且不一致。哺乳期的影响似乎仅限于有长期哺乳史的绝经前女性，但大多数关于这种关系的研究在统计效力方面存在局限性。我们进行了一项多中心、基于人群的病例对照研究，样本量足够大，以便更精确地描述哺乳期与乳腺癌风险之间的关联。
从威斯康星州、马萨诸塞州、缅因州和新罕布什尔州的全州肿瘤登记处识别出年龄小于75岁的乳腺癌患者。如果病例对象小于65岁，则从持牌司机名单中随机选择对照；如果他们年龄在65至74岁之间，则从医疗保险受益人名单中随机选择对照。通过电话访谈获取有关哺乳、生殖史以及家族和病史的信息。在排除未生育的女性后，剩余5878例病例对象和8216例对照用于分析。
在调整了产次、首次分娩年龄和其他乳腺癌风险因素后，与有生育史但从未哺乳的女性相比，哺乳期与绝经前女性患乳腺癌风险略有降低相关（相对风险，0.78；95%置信区间，0.66至0.91）；有哺乳史的绝经后女性与未哺乳的绝经后女性相比，患乳腺癌的相对风险为1.04（95%置信区间，0.95至1.14）。随着累计哺乳时间的增加，绝经前女性患乳腺癌的风险降低（趋势P值<0.001），但在绝经后有生育史的女性中未降低（趋势P值=0.51）。首次哺乳年龄较小与绝经前乳腺癌风险降低显著相关（趋势P值=0.003）。与有生育史但未哺乳的女性相比，首次哺乳年龄小于20岁且总共哺乳婴儿六个月以上的女性患乳腺癌的相对风险为0.54（95%置信区间，0.36至0.82）。
有哺乳史的绝经前女性患乳腺癌的风险降低。有哺乳史的绝经后女性患乳腺癌的风险未降低。
