Tumor-Educated Platelet RNA and Circulating Free RNA: Emerging Liquid Biopsy Markers for Different Tumor Types

The incidence and mortality from malignant tumors continue to rise each year. Consequently, early diagnosis and intervention are vital for improving patient' prognosis and survival. The traditional pathological tissue biopsy is currently considered the gold standard for cancer diagnosis. However, it suffers from several limitations including invasiveness, sometimes not repeatable or unsuitable, and the inability to capture the dynamic nature of tumors in terms of space and time. Consequently, these limit the application of tissue biopsies for the diagnosis of early-stage tumors and have redirected the research focus towards liquid biopsies. Blood-based liquid biopsies have thus emerged as a promising option for non-invasive assessment of tumor-specific biomarkers. These minimally invasive, easily accessible, and reproducible tests offer several advantages, such as being mostly complication-free and efficient at monitoring tumor progression and tracing drug resistance. Liquid biopsies show great potential for cancer prediction, diagnosis, and prognostic assessment. Circulating tumor-educated platelets (TEPs) possess the unique ability to absorb nucleic acids from the bloodstream and to modify transcripts derived from megakaryocytes in response to external signals. In addition, circulating free RNA (cfRNA) constitutes a significant portion of the biomolecules present in the bloodstream. This paper aims to provide a comprehensive overview of the current research status regarding TEP RNA and cfRNA in liquid biopsies from various tumor types. Our analysis includes cancers of the lung, liver, pancreas, breast, nasopharynx, ovary and colon, as well as multiple myeloma and sarcoma. By synthesizing this information, we intend to establish a solid theoretical foundation for exploring potential applications of circulating RNA as a reliable biomarker for tumor diagnosis and monitoring.