Liquid Biopsies: Detecting Cancer Through a Drop of Blood

 Imagine catching cancer early, monitoring treatment, or detecting relapse before symptoms appear—all with a simple blood test. This vision is coming true through liquid biopsies, which detect circulating tumor DNA (ctDNA) and tumor-derived exosomes in the bloodstream.

ctDNA carries genetic mutations and epigenetic changes from cancer cells shed into the bloodstream. Highly sensitive technologies like digital PCR and next-generation sequencing (NGS) can now detect even small amounts, enabling early identification of residual disease that conventional tests might miss.

A landmark study in colorectal cancer showed that patients with detectable ctDNA after surgery were far more likely to relapse. Those without detectable ctDNA had excellent long-term outcomes with minimal additional treatment. Inversely, rising ctDNA levels during therapy often precede clinical relapse, giving doctors a vital head-start to intervene.

Liquid biopsies also help guide targeted therapies. For example, in lung cancer patients treated with EGFR inhibitors, detecting specific resistance mutations (like T790M) in ctDNA can signal when to switch drugs—sometimes even before scans show progression.

However, liquid biopsies aren’t flawless. ctDNA may be undetectable in early-stage or low-tumor-burden cases, and distinguishing tumor-derived signals from benign releases or clonal hematopoiesis mutations can be tricky. But as algorithms improve and sequencing becomes cheaper, accuracy is climbing.

In the future, liquid biopsies might be used in routine cancer screening, especially for high-risk individuals. Combined with AI-driven multi-marker analysis, they may detect cancer years earlier than standard care—a revolution in early detection and personalized intervention.