Triple-negative breast cancers (TNBC) accounts for up to 20% of breast cancer cases. These tumors are negative for estrogen, progesterone, and HER2 receptors, which are markers used for diagnosis and treatment of other types of breast cancer. Clinically, TNBCs are notoriously aggressive, respond poorly to targeted therapies, have high rates of relapse, as well as poor prognosis. The molecular basis of TNBC oncogenesis is currently unknown, but it is possible that viral factors, such as Epstein-Barr Virus (EBV) miRNAs, play a role. EBV miRNAs have been implicated in the oncogenesis of several forms of cancer, including Burkitt’s lymphoma and nasopharyngeal carcinoma. The objective of this study, therefore, was to determine the differential expression of EBV miRNAs in TNBC tumors as compared to normal breast tissue. We conducted a comprehensive profiling of viral miRNAs in 48 TNBC tumors as compared to 15 control normal breast tissues, utilizing deep sequencing analysis software and publically available deep sequencing data. Four EBV miRNAs (BART18-3p, BART 8-5p, BART15, BART22) were significantly expressed in 11-17% of the TNBC tumors, and not in control normal breast tissue. Four novel putative EBV miRNAs were found to be differentially expressed in TNBC tumors as compared to control normal cells. Two of the novel putative EBV miRNAs were differentially expressed above 125 reads per million (RPM) in 20% and 27% of the TNBC tumors as compared to 0% and 6.6% of normal breast tissues, respectively. One novel putative EBV miRNA was expressed above 125 RPM in 83% of TNBC tumors as compared to 13% of normal breast tissue. One novel putative EBV miRNA was expressed above 125 RPM in 66% of the normal breast tissue as compared to 2% of the TNBCs. These putative EBV miRNAs localize within genomic regions of EBV, including the LMP-2 region. Ongoing work has so far computationally validated one of these miRNAs as a novel EBV miRNA; in vitro validation studies are in progress. This is the first report on the differential expression of EBV miRNAs in TNBC tumors. Since TNBC tumors are extremely heterogeneous, it is intriguing that 20% of TNBC tumors specifically express the same EBV miRNA. Our findings suggest that these differentially expressed EBV miRNAs may potentially play a role in the pathogenesis of TNBC.

Citation Format: Alexander Blanchard, Tiffany Walls, Ramon Vidal, Stefan Bonn, Scott Harrison, Perpetua Muganda. Differential expression of Epstein Barr virus miRNAs in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1566. doi:10.1158/1538-7445.AM2017-1566