Previous studies have shown that let-7 can repress the post-transcriptional translation of LIN28, and LIN28 in turn could block the maturation of let-7, forming a double-negative feedback loop. In this study, we investigated the effect of germline genetic variants on regulation of the homeostasis of the let-7/LIN28 loop and breast cancer risk. We initially demonstrated that the T/C variants of rs3811463, a single nucleotide polymorphism (SNP) located near the let-7 binding site in LIN28, could lead to differential regulation of LIN28 by let-7. Specifically, the C allele of rs3811463 weakened let-7–induced repression of LIN28 mRNA, resulting in increased production of LIN28 protein, which could in turn down-regulate the level of mature let-7. This effect was then validated at the tissue level in that the normal breast tissue of individuals with the rs3811463-TC genotype expressed significantly lower levels of let-7 and higher levels of LIN28 protein than those individuals with the rs3811463-TT genotype. Because previous in vitro and ex vivo experiments have consistently suggested that LIN28 could promote cellular transformation, we then systematically evaluated the relationship between rs3811463 as well as other common LIN28 SNPs and the risk of breast cancer in a stepwise manner. The first hospital-based association study (n = 2,300) demonstrated that two SNPs were significantly associated with breast cancer risk, one of which was rs3811463, while the other was rs6697410. The C allele of the rs3811463 SNP corresponded to an increased risk of breast cancer with an odds ratio (OR) of 1.25 (P = 0.0091), which was successfully replicated in a second independent study (n = 1,156) with community-based controls. The combined P-value of the two studies was 8.0×10−5. Taken together, our study demonstrates that host genetic variants could disturb the regulation of the let-7/LIN28 double-negative feedback loop and alter breast cancer risk.

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The association between single-nucleotide polymorphisms (SNPs) in the interleukin-10 (IL-10) gene promoter and breast cancer risk is still ambiguous. We here performed a meta-analysis based on the evidence currently available from the literature to make a more precise estimation of the relationship between two genetic variants in the IL-10 gene promoter, -1082A > G (rs1800896) and -592C > A (rs1800872), and breast cancer. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the corresponding strengths of association under the codominant, dominant, and recessive models. A total of ten studies (4,181 cases and 4,384 controls) were eligible for meta-analysis. There were six studies with 3,032 cases and 3,190 controls for rs1800872, and eight studies with 1,636 cases and 1,670 controls for rs1800896. Meta-analysis showed that neither of the two polymorphisms had any association with increased breast cancer risk (for rs1800896: OR = 1.060, 95% CI = 0.785-1.432 in the dominant model, and OR = 1.152, 95% CI = 0.958-1.386 in the recessive model; and for rs1800872: OR = 0.952, 95% CI = 0.859-1.056 in the dominant model, and OR = 0.892, 95% CI = 0.741-1.072 in the recessive model). The results did not change when the analyses were restricted in Caucasians, or in the studies fulfilling Hardy-Weinberg equilibrium, or according to source of controls. In outlier analysis, no individual study affected the overall OR dominantly, since omission of any single study made no material huge difference. In conclusion, the present meta-analysis suggests a lack of association between the two SNPs (rs1800896 and rs1800872) in the IL-10 gene promoter and breast cancer risk. Further studies, either with larger sample size or regarding other SNPs/haplotypes within the IL-10 gene, are needed to clarify the role of IL-10 in breast carcinogenesis.

Toll-like receptor 3 (TLR3) is a viral sensor that induces apoptosis in response to double-stranded RNA (dsRNA). Common genetic changes in the TLR3 gene may influence breast cancer susceptibility and development. However, all of the polymorphisms in the previous study were only markers of the TLR3 gene, not causative polymorphisms. In this study, we performed a case-control study focusing on the relationship between rs5743305 (−926T>A), a single nucleotide polymorphism (SNP) in the promoter region of TLR3, and breast cancer. We found that the genetic variant rs5743305 increased the risk of breast cancer under the dominant and codominant models (dominant model: