Overview Malignant tumors are serious diseases endangering human health. Early detection and diagnosis is the key to improve the 5-year survival rate of cancer patients, which is an urgent problem to be solved clinically. However, the methods available for the early diagnosis of cancer are very limited at present. Therefore, the importance of developing useful diagnostic and monitoring tools should be emphasized to improve the clinical outcome of patients with cancer. Recently, the emergence of tumor liquid biopsy, such as cell-free DNA, RNA and mitochondrial DNA, open up new possibilities for the non-invasive detection of various human cancers. These promising markers are considered to possess great potential and could facilitate therapeutic strategies for cancer including the following: early detection of diseases, predication of prognostic outcome, monitoring of tumor dynamics and development of novel targeted treatments. Meanwhile, the rapid development of molecular biology technology promotes the realization of liquid biopsy techniques as non-invasive molecular diagnostic markers. In summary, this topic focuses on tumor liquid biopsy to help us understand the research hotspots, latest developments and potential clinical applications.