Liquid Biopsy: minimal-invasive analysis of somatic alterations

Liquid biopsy enables minimally invasive analysis of disease-associated biomarkers from body fluids, focusing on CTCs, cfDNA, and EVs. While blood is the primary source, these analytes can also be detected in other fluids such as urine, CSF, and saliva. The purpose of this editorial is to contextualize the clinical relevance and technological advances of liquid biopsy, highlight its importance for human genetics, and introduce this special issue summarizing current applications and emerging methods across oncology, prenatal testing, and genetic diagnostics.

- Circulating tumor cells (CTCs) are the earliest recognized liquid biopsy analyte (first described in 1869). Historically linked to metastatic biology, CTC enumeration has become a predictive marker for cancer monitoring, and single-cell analyses enable functional characterization. - Circulating free DNA (cfDNA) and extracellular vesicles (EVs) are released by many cell types, broadening applicability beyond cancer. EVs carry biologically informative cargo reflective of viable cells but face challenges due to difficulties in standardizing isolation, which currently limits diagnostic use. - cfDNA is readily accessible and has become the most promising analyte in clinical practice, underpinning applications such as disease monitoring in cancer, NIPT, and genetic diagnosis of mosaic disorders. - In oncology, ESMO recommends using circulating tumor DNA (ctDNA) assays to detect actionable variants for CDx across several cancers; in Germany, ctDNA testing is reimbursed in specific scenarios in NSCLC and breast cancer. ctDNA supports minimal residual disease (MRD) detection, recurrence monitoring, and treatment response assessment. Prospective studies have shown promising results for ctDNA-guided adjuvant therapy decisions in early-stage colorectal cancer and treatment adaptation upon detection of resistance markers in metastatic breast cancer. - Beyond oncology, cfDNA-based liquid biopsy supports NIPT for fetal genetic alterations and aids in diagnosing monogenic mosaic diseases, with additional applications in transplant surveillance.

- CTCs, cfDNA, and EVs are key analytes in liquid biopsy; blood is the main matrix but other body fluids can be used. - CTCs are cancer-specific; enumeration serves as a predictive marker, and single-cell approaches enable functional profiling. - EVs contain functional cargo reflective of disease biology, but lack of standardized isolation methods limits current diagnostic deployment. - cfDNA is the most clinically advanced analyte due to accessibility and technological progress, enabling applications in oncology (CDx, MRD, monitoring), NIPT, and mosaic disease diagnostics. - Clinical guidance supports ctDNA testing for actionable variants (ESMO recommendations). In Germany, ctDNA tests are reimbursed in defined NSCLC and breast cancer settings. - Prospective trials demonstrate the utility of ctDNA to guide adjuvant therapy in early colorectal cancer and to adapt therapy upon resistance detection in metastatic breast cancer.

The synthesis underscores liquid biopsy’s utility across oncology and human genetics, with cfDNA currently leading clinical adoption. The findings align with the goal of enabling personalized medicine through minimally invasive, repeatable testing that captures tumor dynamics (for CDx, MRD, and monitoring) and supports genetic applications such as NIPT and mosaic disease diagnosis. However, clinical translation hinges on rigorous analytical validation and standardization—particularly crucial for high-sensitivity cfDNA assays and for overcoming pre-analytical and isolation challenges with EVs. Educating genetics professionals in molecular medicine is emphasized to ensure high-quality interpretation and integration of liquid biopsy results into clinical care.

This special issue consolidates advances in technologies and applications of liquid biopsy, highlighting cfDNA as the current diagnostic mainstay while reviewing the roles of CTCs and EVs. It emphasizes the importance of analytical validation and standardization to support clinical interpretation and personalized care in human genetics and oncology. Future efforts should focus on harmonizing pre-analytical and analytical workflows, improving EV isolation standardization, expanding evidence for ctDNA-guided decision-making across indications, and integrating liquid biopsy into routine genetic diagnostics with appropriate training for clinicians and laboratory professionals.

The article is an editorial overview and does not present original empirical data. Field-wide limitations highlighted include: (1) lack of standardized, validated methods for EV isolation hindering diagnostic use; (2) the requirement for highly sensitive, rigorously validated cfDNA assays to ensure reliable clinical interpretation; and (3) potential interpretational complexity because cfDNA derives from multiple tissues, which can complicate attribution of signal to specific disease processes.