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Cholangiocarcinoma (CCA) is a lethal malignancy originating from the biliary tract epithelium. Most patients are diagnosed at an advanced stage. Even after resection with curative intent, prognosis remains poor. Previous studies have reported the evolving role of miRNAs as novel biomarkers in cancer diagnosis, prognostication and chemotherapy response. Various miRNAs, such as miR-21, miR-26, miR-122 and miR-150, have been identified as possible blood-based biomarkers for noninvasive diagnosis of CCA. Moreover, epithelial-mesenchymal transition (EMT)- and angiogenesis-associated miRNAs have been implicated in tumor cell dissemination and are able to determine clinical outcome. In fact, miRNAs involved in cell survival might even determine chemotherapy response. This review provides an overview of known miRNAs as CCA-specific biomarkers.

Over the past decade, major advances in our comprehension of breast cancer biology have led to improved diagnostic and prognostic techniques and the development of novel targeted therapies. However, the efficacy of new treatments remains limited by a combination of drug toxicity, resistance and persisting insufficiencies in our understanding of tumor-signaling pathways; furthermore, the reliability of identified biomarkers is contentious. Following their recent discovery, miRNAs have been established as critical regulators of gene expression, and their putative roles as oncogenes and tumor-suppressor genes has provided a potential new dimension to our clinical approach to breast cancer diagnosis and treatment. Their role as biomarkers and therapeutic targets is appealing; however, several barriers have limited our ability to translate this potential into a clinical reality. This review focuses on the currently accepted roles of miRNAs in breast cancer pathogenesis, and highlights the clinical challenges and breakthroughs in this field to date.