Progress and Compliance Considerations of Tumor Companion Diagnostic Factor Detection Kits in the Field of Liquid Biopsy

The Integration Trend of Liquid Biopsy and Companion Diagnostics

Traditional tumor companion diagnostics rely on tissue biopsy, but are limited by sampling difficulty, tumor heterogeneity, and the feasibility of repeat biopsy. Liquid biopsy technology, by analyzing circulating tumor DNA (ctDNA), circulating tumor cells, or nucleic acid factors in exosomes in body fluids such as peripheral blood and pleural/ascitic fluid, provides a non-invasive or minimally invasive alternative for companion diagnostics. The application of tumor companion diagnostic factor detection kits in the field of liquid biopsy is gradually expanding, and they can be used not only for detecting driver mutations at initial diagnosis, but also for drug resistance monitoring and minimal residual disease assessment during treatment. Currently common liquid biopsy companion diagnostic factors include EGFR mutations, KRAS mutations, BRAF mutations, etc. Their detection sensitivity is typically at the 0.1%-0.5% variant allele frequency level, and consistency with tissue biopsy results can reach over 90%.

Technical Characteristics of Detection for Factors Such as ctDNA

The design of liquid biopsy kits needs to address issues such as fragmented DNA sources and limited total amount. Commonly used technologies include digital PCR and high-sensitivity high-throughput sequencing. Digital PCR, through compartmentalization followed by independent amplification, can achieve absolute quantification and is suitable for detecting known hotspot mutations; while high-throughput sequencing can simultaneously discover unknown mutations and has broader coverage. In addition to ctDNA, ctRNA detection can be used to assess fusion genes or splicing variants; miRNA or lncRNA in exosomes are also gradually being included in research scope, but the factors entering clinical kits are still mainly ctDNA. During the R&D stage, kits generally require optimization of parameters such as sample processing, library construction, and sequencing depth to ensure stable detection even at low input amounts. For example, for ctDNA extraction kits, recovery efficiency and fragment distribution under different plasma volumes (conventionally 2-5 mL) need to be validated.

Performance Validation Requirements in Kit R&D

According to relevant medical device registration guidelines, liquid biopsy companion diagnostic kits must complete detailed performance validation. This includes: analytical sensitivity (limit of detection), analytical specificity (cross-reactivity), precision (repeatability and reproducibility), accuracy (comparison with orthogonal methods or tissue testing), and stability (sample storage conditions and freeze-thaw cycles). It is worth noting that because liquid biopsy samples may contain DNA derived from normal leukocytes, kits need to have the ability to distinguish mutation signals. In addition, for multi-gene detection kits, the functional validation parameters for each factor should be set separately and cannot simply be based on overall sample data. Kit instructions should clearly state the applicable sample types, anticoagulant types, transport and storage conditions, etc., to avoid deviations in actual use.

Key Compliance Points for Medical Device Registration and Clinical Evaluation

In China, tumor companion diagnostic factor detection kits are managed as Class III medical devices and require submission of clinical trial or clinical evaluation materials. Clinical evaluation of liquid biopsy kits usually adopts prospective or retrospective study designs, using tissue biopsy or approved kit results as controls to evaluate sensitivity and specificity. Because liquid biopsy may produce false negatives due to tumor heterogeneity or clonal evolution, the clinical intended use of the kit should be limited to "adjunctive diagnosis" rather than "replacement diagnosis." In registration applications, quality management system documents, production environment facility validation, and batch-to-batch consistency data must also be provided. For supporting reagents involving multiple manufacturers (such as extraction reagents and detection reagents), clear authorization or joint validation is required. In addition, adverse events must be continuously collected after market launch, and clinical performance data must be updated regularly.

Overall, tumor companion diagnostic factor detection kits have broad application prospects in liquid biopsy, but regulatory requirements must be strictly followed to ensure the reliability and clinical interpretability of test results.