Liquid Biopsy in Oncology: Circulating Analytes, Emerging Platforms, and the Road to Clinical Implementation

Background. Cancer's global burden is rising, including in India. Tissue biopsy, the diagnostic standard, is invasive, non-repeatable, and captures limited heterogeneity. Liquid biopsy - analysis of tumour-derived material in body fluids - offers a minimally invasive alternative for diagnosis, prognosis, and longitudinal monitoring. Objective. This review synthesised the scientific basis, platforms, applications, and laboratory-integration challenges of liquid biopsy, emphasising clinical-biochemistry practice and regulatory, ethical, and economic considerations in low- and middle-income countries (LMICs). Methods. PubMed, Scopus, Web of Science, and Google Scholar were searched (January 2008-October 2025) for English-language peer-reviewed articles on liquid biopsy, circulating tumour DNA and cells, extracellular vesicles, tumour-educated platelets, cell-free DNA, and multi-cancer early detection; seminal references were retained. Results. Five analyte classes emerged: circulating tumour cells, circulating tumour DNA, cell-free RNA and microRNAs, extracellular vesicles, and tumour-educated platelets. Digital droplet PCR, next-generation sequencing, CRISPR assays, mass-spectrometry proteomics, and nano-biosensors achieve near-attomolar sensitivity. Applications span multi-cancer early detection, companion diagnostics, minimal-residual-disease surveillance, resistance monitoring, and paediatric oncology. Barriers include pre-analytical variability, clonal haematopoiesis of indeterminate potential, absent harmonisation, and limited affordability in LMICs. Conclusion. Liquid biopsy is repositioning cancer diagnostics towards minimally invasive, real-time, longitudinal care. Wider translation requires pre-analytical standardisation, robust bioinformatics, equitable access, and regulatory harmonisation.