Palmer Julie R, Wise Lauren A, Horton Nicholas J, Adams-Campbell Lucile L, Rosenberg Lynn
Slone Epidemiology Center, Boston University, Boston, MA 02215, USA.
J Natl Cancer Inst. 2003 Mar 19;95(6):478-83. doi: 10.1093/jnci/95.6.478.
In the United States, breast cancer incidence is higher among African-American women than among white women before age 45 but lower at older ages. To explore whether differences in childbearing patterns can explain this observation, we assessed the relation of several childbearing variables to breast cancer risk in a large prospective cohort study of U.S. African-American women.
Black Women's Health Study participants were enrolled in 1995 and were followed by mailed questionnaires every 2 years (in 1997 and 1999). Of the 64,500 women enrolled, 56,725 (88%) completed at least one of the follow-up questionnaires. During 214,862 person-years of follow-up, participants reported 349 breast cancers, of which 128 were among women younger than 45 years and 221 were among women aged 45-70 years. Incidence rate ratios (IRRs) with 95% confidence intervals (CIs) were derived from age-stratified Cox regression models that adjusted for each of the childbearing variables (parity, age at first birth, and time since last birth).
Compared with primiparity, high parity was associated with an increased risk of breast cancer among women younger than 45 years (IRR for four or more births = 2.4, 95% CI = 1.1 to 5.1) and a decreased risk among women aged 45 years and older (IRR = 0.5, 95% CI = 0.3 to 0.9). The IRR for late age at first birth compared with early age was 2.5 (95% CI = 1.1 to 5.8) among the younger women and was not elevated among older women. We found no statistically significant association of time since last birth with breast cancer risk among either younger or older women.
Parity has a dual association with breast cancer risk in African-American women; among women younger than 45 years, parity is associated with an increased risk and among women 45 years and older it is associated with a decreased risk. This dual effect may explain some of the observed differences in breast cancer incidence rates among African-American and white women.
在美国，45岁之前非裔美国女性的乳腺癌发病率高于白人女性，但在年长女性中则较低。为了探究生育模式的差异是否能够解释这一现象，我们在美国非裔女性的一项大型前瞻性队列研究中评估了几个生育变量与乳腺癌风险之间的关系。
黑人女性健康研究的参与者于1995年入组，每两年通过邮寄问卷进行随访（1997年和1999年）。在入组的64,500名女性中，56,725名（88%）完成了至少一份随访问卷。在214,862人年的随访期间，参与者报告了349例乳腺癌，其中128例发生在45岁以下的女性中，221例发生在45至70岁的女性中。发病率比（IRR）及其95%置信区间（CI）来自年龄分层的Cox回归模型，该模型对每个生育变量（产次、初产年龄和末次生育后的时间）进行了调整。
与初产相比，高生育次数与45岁以下女性患乳腺癌的风险增加相关（四次或更多次生育的IRR = 2.4，95%CI = 1.1至5.1），而与45岁及以上女性的风险降低相关（IRR = 0.5，95%CI = 0.3至0.9）。初产年龄晚与初产年龄早相比，年轻女性的IRR为2.5（95%CI = 1.1至5.8），而老年女性中未升高。我们发现末次生育后的时间与年轻或老年女性的乳腺癌风险均无统计学上的显著关联。
产次与非裔美国女性的乳腺癌风险存在双重关联；在45岁以下的女性中，产次与风险增加相关，而在45岁及以上的女性中，产次与风险降低相关。这种双重效应可能解释了非裔美国女性和白人女性在乳腺癌发病率方面观察到的一些差异。
