Promising Blood-Based Biomarkers for Melanoma: Recent Progress of Liquid Biopsy and Its Future Perspectives

Because the recent success of novel therapeutic approaches has dramatically changed the clinical management of melanoma, less invasive and repeatable monitoring tools that can predict the disease status, drug resistance, and the development of side effects are increasingly needed. As liquid biopsy has enabled us to diagnose and monitor disease status less invasively, substantial attention has been directed toward this technique, which is gaining importance as a diagnostic and/or prognostic tool. It is evident that microRNA, cell-free DNA, and circulating tumor cells obtained via liquid biopsy are promising diagnostic and prognostic tools for melanoma, and they also have utility for monitoring the disease status and predicting drug effects. Although current challenges exist for each biomarker, such as poor sensitivity and/or specificity and technical problems, recent technical advances have increasingly improved these aspects. For example, next-generation sequencing technology for detecting microRNAs or cell-free DNA enabled high-throughput analysis and provided significantly higher sensitivity. In particular, cancer personalized profiling by deep sequencing for quantifying cell-free DNA is a promising method for high-throughput analysis that provides real-time comprehensive data for patients at various disease stages. For wide clinical implementation, it is necessary to increase the sensitivity for the markers and standardize the assay procedures to make them reproducible, valid, and inexpensive; however, the broad clinical application of liquid biopsy could occur quickly. This review focuses on the significance of liquid biopsy, particularly related to the use of blood samples from patients with melanoma, and discusses its future perspectives.