MicroRNAs (miRNAs) are attractive, short, non-coding RNAs widely studied for their fundamental roles in tissue homeostasis, cell proliferation, and dysregulation in cancer. A vast majority of investigations and technical improvements have focused on miRNAs' tumor-specific expression patterns, which provide novel molecular biomarkers for cancer detection and targeted therapies. In this review, we focus on recent achievements in biomarker validation and potential for cancer treatment, with special trend in non-invasive strategies to evaluate miRNAs, especially for diagnostic and prognostic applications. We further include a large compilation of PubMed data regarding microRNAs reported as diagnostic or prognostic cancer biomarkers in at least three studies.