Background Breast cancer is reported as one of the most common cancers among females worldwide. Infectious agents especially viruses have been considered as role players in the development of breast cancer. Although some investigations suggest an association between bovine leukemia virus (BLV) and breast cancer, the involvement of this virus as a risk factor remains controversial. The present study aimed to find out any possible association between BLV and breast cancer through conducting a systematic review and meta-analysis. Methods Systematic literature search was performed by finding related case-control articles from the PubMed, Google Scholar, Web of Science, Scopus, and EMBASE databases. The heterogeneity and the multivariable-adjusted OR and corresponding 95% CI were applied by meta-analysis and forest plot across studies. All statistical analyses were performed using Stata 14.1. Result Based on a comprehensive literature search, 9 case-control studies were included for meta-analysis. The combination of all included studies showed that BLV infection is associated with an increased risk of breast cancer [summary OR (95% CI) 2.57 (1.45, 4.56)]. Conclusion This is the first meta-analysis to analyze a potential association between BLV infection and the risk of breast cancer. Control of the infection in cattle herds and screening of the milk and dairy products may help to reduce the transmission of the virus to humans.

中文翻译：

---

牛白血病病毒 (BLV) 与乳腺癌风险：病例对照研究的系统评价和荟萃分析

背景 据报道，乳腺癌是全世界女性中最常见的癌症之一。传染性病原体，尤其是病毒已被认为是乳腺癌发展中的角色。尽管一些研究表明牛白血病病毒 (BLV) 与乳腺癌之间存在关联，但这种病毒作为危险因素的参与仍然存在争议。本研究旨在通过系统评价和荟萃分析找出 BLV 与乳腺癌之间可能存在的关联。方法 通过从 PubMed、Google Scholar、Web of Science、Scopus 和 EMBASE 数据库中查找相关病例对照文章进行系统文献检索。通过荟萃分析和森林图在研究中应用异质性和多变量调整的 OR 和相应的 95% CI。所有统计分析均使用 Stata 14.1 进行。结果 综合文献检索，纳入9篇病例对照研究进行荟萃分析。所有纳入研究的结合表明，BLV 感染与乳腺癌风险增加有关 [总结 OR (95% CI) 2.57 (1.45, 4.56)]。结论 这是第一个分析 BLV 感染与乳腺癌风险之间潜在关联的荟萃分析。控制牛群的感染并筛查牛奶和奶制品可能有助于减少病毒向人类的传播。所有纳入研究的结合表明，BLV 感染与乳腺癌风险增加有关 [总结 OR (95% CI) 2.57 (1.45, 4.56)]。结论 这是第一个分析 BLV 感染与乳腺癌风险之间潜在关联的荟萃分析。控制牛群的感染并筛查牛奶和奶制品可能有助于减少病毒向人类的传播。所有纳入研究的结合表明，BLV 感染与乳腺癌风险增加有关 [总结 OR (95% CI) 2.57 (1.45, 4.56)]。结论 这是第一个分析 BLV 感染与乳腺癌风险之间潜在关联的荟萃分析。控制牛群的感染并筛查牛奶和奶制品可能有助于减少病毒向人类的传播。