Tumor microRNA expression profiling identifies circulating microRNAs for earlier breast cancer detection

Due to their role in tumorigenesis and remarkable stability in body fluids, microRNAs (miRNAs) are emerging as a promising diagnostic tool. The aim of this study was to identify tumor miRNA signatures for the discrimination of breast cancer and the intrinsic molecular subtypes, and the study in plasma of the status of the most significant ones in order to identify potential circulating biomarkers for breast cancer detection. MiRNA expression profiling of 1919 human miRNAs was conducted in 122 FFPE breast tumors (31 luminal A, 33 luminal B, 27 Her2 and 31 triple negative) and 11 normal breast tissues using LNA based miRNA microarrays. Breast tumors were divided into a training (n=61) and a test set (n=61). Both series comprised a similar number of samples from each molecular subtype. Differential expression analysis was performed and microarray classifiers were developed with samples from the training set and validated in samples from the test set. The most relevant miRNAs were validated by quantitative PCR and analyzed in plasma from 36 pretreated patients, 47 postreated patients and 26 healthy individuals. In addition, further validation in 114 pretreated patients and 116 healthy individuals was performed.