Abstract
Breast cancer is the second leading cause of cancer deaths among women. Multiple microRNAs (miRNAs) have been reported to be associated with breast cancer progression or metastasis. The purpose of the current study was to identify plasma extracellular miRNAs associated with incident breast cancer. Levels of 166 plasma miRNA were measured using qRT-PCR in 2140 Framingham Heart Study female participants with a median follow up of 15.7 years. Prospective analyses of the associations of miRNAs with the occurrence of 56 new-onset breast cancer events were conducted using proportional hazards regression. The expression levels miR-134-5p (P=0.002) and miR-505-3p (P=0.005) were found to be positively associated with incident breast cancer after adjusting for age, body mass index, and cigarette smoking. These results highlight plasma miRNAs as potential biomarkers of breast cancer risk. Validation of these findings in larger and more diverse cohorts is warranted.