Abstract P4-07-02: Expression of miR-18a and miR-210 in normal breast tissue as candidate markers of breast cancer risk

Purpose: miRNAs are non-coding RNAs that are abnormally expressed in breast cancer, with critical roles in cancer due to their regulation of large gene networks. miRNA expression in benign high-risk breast tissue has never been evaluated, but it may provide information about early dysregulation events that contribute to breast cancer risk. The contralateral unaffected breast (CUB) of women with unilateral breast cancer is in high-risk for the second primary cancer. Thus, we examined miRNA expression profiles in tumor and the matching CUBs to seek potential miRNA biomarkers for breast cancer risk. Methods: FFPE tissues of breast cancer and their matching CUB tissues were sectioned. The areas of tumor and normal ductal epithelium were outlined and then dissected using laser microdissection system. Total RNA was extracted for miRNA profiling studies. Expression profiles of 754 mature miRNAs were examined using TaqMan Low Density Arrays assays in 30 paired breast cancer and CUB samples (15 with ER+ tumors, 15 with ER- tumors) and 15 reduction mammoplasty (RM) controls, matched by age, race and menopausal status. ANOVA test was performed to examine the differential expression among groups and pairwise comparison with Sidak adjustment was used for multiple comparison. Seven candidate miRNAs were then examined in an independent CUB sample set (20 with ER+ tumors, 20 with ER- tumors) and 20 RM controls. Further independent validation was performed using qRT-PCR in 80 benign breast biopsy (BBB) samples: 40 from women who subsequently developed breast cancer (cases) and 40 from those who did not (controls). Logistic regression analysis and receiver operating characteristic (ROC) analysis were performed using combinations of the expression of multiple miRNAs to establish models discriminating cases from controls. Results: Seven miRNAs (miR-18a, miR-210, miR-214*, miR-124, miR-193a-3p, miR485-3p and miR-671-3p) were found to be differentially expressed in breast cancer and CUB samples vs. RM samples in the discovery sample set. Among them, miR-18a and miR-210 were validated in a second, independent CUB sample set. The expression of miR-18a and miR-210 were significantly higher in tumor (regardless ER status) compared to CUBs and RM controls. The expression levels in CUBs were significantly higher than in RM. We then examined miR expression in case BBB samples, and confirmed that expression of miR-18a and miR-210 were increased compared with controls. ROC analysis using miR-18a and miR-210 discriminated high-risk cases from standard-risk controls with OR 2.44, P = 0.022. Conclusion: The expression of miR-18a and miR-210 were elevated in breast cancer, in matched CUBs, and in BBB predating cancer diagnosis. These data provide strong support for the hypothesis that miR-18a and miR-210 expression in BBB is an indicator of increased risk of breast cancer. Given the high expression in tumors, they are also potential cancer detection biomarkers. Citation Format: Wang J, Shidfar A, Costa FF, Scholtens D, Bischof JM, Sullivan ME, Ivancic D, Soares MB, Khan SA. Expression of miR-18a and miR-210 in normal breast tissue as candidate markers of breast cancer risk [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-07-02.