The important possibility that microRNA signatures may prove to be novel cancer biomarkers is apparent from this study's preliminary finding that unique sets of miRNAs are associated with breast cancers currently defined by their ErbB2 status (let-7f, let-7g, miR-107, mir-10b, miR-126, miR-154 and miR-195) or their ER/PRstatus (miR-142-5p, miR-200a, miR-205 and miR-25). This evidence concerns the gene ERBB2 and breast cancer.