Importance Breastfeeding has been associated with a reduced risk of epithelial ovarian cancer in multiple studies, but others showed no association. Whether risk reduction extends beyond that provided by pregnancy alone or differs by histotype is unclear. Furthermore, the observed associations between duration and timing of breastfeeding with ovarian cancer risk have been inconsistent.

Objective To determine the association between breastfeeding (ie, ever/never, duration, timing) and ovarian cancer risk overall and by histotype.

Design, Setting, and Participants A pooled analysis of parous women with ovarian cancer and controls from 13 case-control studies participating in the Ovarian Cancer Association Consortium was performed. Odds ratios (ORs) and 95% CIs of the overall association were calculated using multivariable logistic regression and polytomous logistic regression for histotype-specific associations. All data were collected from individual sites from November 1989 to December 2009, and analysis took place from September 2017 to July 2019.

Exposures Data on breastfeeding history, including duration per child breastfed, age at first and last breastfeeding, and years since last breastfeeding were collected by questionnaire or interview and was harmonized across studies.

Main Outcomes and Measures Diagnosis of epithelial ovarian cancer.

Results A total of 9973 women with ovarian cancer (mean [SD] age, 57.4 [11.1] years) and 13 843 controls (mean [SD] age, 56.4 [11.7] years) were included. Breastfeeding was associated with a 24% lower risk of invasive ovarian cancer (odds ratio [OR], 0.76; 95% CI, 0.71-0.80). Independent of parity, ever having breastfed was associated with reduction in risk of all invasive ovarian cancers, particularly high-grade serous and endometrioid cancers. For a single breastfeeding episode, mean breastfeeding duration of 1 to 3 months was associated with 18% lower risk (OR, 0.82; 95% CI, 0.76-0.88), and breastfeeding for 12 or more months was associated with a 34% lower risk (OR, 0.66; 95% CI, 0.58-0.75). More recent breastfeeding was associated with a reduction in risk (OR, 0.56; 95% CI, 0.47-0.66 for <10 years) that persisted for decades (OR, 0.83; 95% CI, 0.77-0.90 for ≥30 years; P for trend = .02).

Conclusions and Relevance Breastfeeding is associated with a significant decrease in risk of ovarian cancer overall and for the high-grade serous subtype, the most lethal type of ovarian cancer. The findings suggest that breastfeeding is a potentially modifiable factor that may lower risk of ovarian cancer independent of pregnancy alone.

重要性 在多项研究中，母乳喂养与降低上皮性卵巢癌的风险有关，但其他研究显示没有相关性。风险降低是否超出仅由妊娠提供的范围或因组织型而不同尚不清楚。此外，观察到的母乳喂养时间和时间与卵巢癌风险之间的关联并不一致。

目的 确定母乳喂养（即曾经/从不、持续时间、时间）与总体和组织型卵巢癌风险之间的关联。

设计、设置和参与者 对参与卵巢癌协会联盟的 13 项病例对照研究的患有卵巢癌的经产妇和对照进行了汇总分析。使用多变量逻辑回归和多变量逻辑回归计算组织型特异性关联的优势比 (OR) 和 95% CI。所有数据均从 1989 年 11 月至 2009 年 12 月从各个站点收集，分析于 2017 年 9 月至 2019 年 7 月进行。

通过问卷或访谈 收集有关母乳喂养历史的数据，包括每个孩子母乳喂养的持续时间、第一次和最后一次母乳喂养的年龄以及自上次母乳喂养以来的年数，并在各个研究中进行协调。

主要结果和措施 上皮性卵巢癌的诊断。

结果 共纳入 9973 名卵巢癌女性（平均 [SD] 年龄，57.4 [11.1] 岁）和 13 843 名对照（平均 [SD] 年龄，56.4 [11.7] 岁）。母乳喂养可使浸润性卵巢癌的风险降低 24%（优势比 [OR]，0.76；95% CI，0.71-0.80）。与产次无关，母乳喂养与所有侵袭性卵巢癌的风险降低有关，特别是高级别浆液性和子宫内膜样癌。对于单次母乳喂养，平均母乳喂养时间为 1 至 3 个月与风险降低 18% 相关（OR，0.82；95% CI，0.76-0.88），母乳喂养 12 个月或更长时间与风险降低 34% 相关（OR，0.66；95% CI，0.58-0.75）。最近的母乳喂养与持续数十年（OR，0.83；95% CI，0.趋势P = .02)。

结论和相关性 母乳喂养与总体卵巢癌风险显着降低有关，对于高级别浆液性亚型，最致命的卵巢癌类型。研究结果表明，母乳喂养是一个可能会降低卵巢癌风险的潜在可改变因素，而与妊娠无关。