Genitourinary Cancer Medical Oncologist, Eastern Health
Senior Research Fellow & Lab Head, Monash University
Cancer isn’t one disease. It’s thousands, each developing and behaving differently. To complicate matters, cancer changes over time, finding new ways around treatments that once worked and adapting to be harder to fight. For this reason, two people with the same cancer diagnosis can have wildly different experiences. A ‘one-size-fits-all’ approach to treating cancer is not the answer.
To tackle this monumental challenge, doctors have traditionally taken a piece of a person’s cancer to study it in detail. These tissue biopsies hold incredible value. By deciphering the genetic makeup of a cancer, we can understand how it grows and where there may be weaknesses that can be exploited with new treatments. Tissue biopsies however have their drawbacks. They can be uncomfortable and carry a small but real risk of bleeding or infection. Importantly, they only capture a single moment in time and cannot be easily repeated as a cancer evolves.
Thankfully, one of the most exciting advances in cancer research today isn’t a new drug. It’s a more convenient way to see how the cancer is behaving in real-time and can be repeated as often as needed. The test is called ctDNA—short for circulating tumour DNA. When cancer cells die, they release tiny fragments of DNA into the bloodstream. A blood test can now pick up these fragments and scientists are able to read their genetic code. Because it uses blood rather than tissue, it’s often called a “liquid biopsy”.
So what can liquid biopsy tell us? First, it can help choose the right treatment for the right patient. The same genetic weaknesses a tissue biopsy might reveal—the vulnerabilities that targeted therapies can exploit—can often be found in ctDNA from a standard blood draw. This means more patients can access personalised treatment decisions, without the delays or difficulties of a surgical biopsy.
ctDNA can also track whether a cancer is responding to treatment. The amount of ctDNA in the blood usually falls when therapy is working and rises when the cancer starts to adapt. That rise can appear many months before a CT scan shows any change, acting as an early warning that gives doctors and patients more time to plan the next step.
Finally, ctDNA can show how a cancer is changing. A ctDNA test taken today can look remarkably different to one taken six months ago, giving doctors a moving picture of the cancer that a single tissue biopsy simply cannot provide.
The test isn’t perfect. Not every person with advanced cancer has detectable ctDNA, and interpreting the results takes specialist expertise. But the field is moving quickly, and researchers are actively addressing the barriers to making liquid biopsy available for every patient who could benefit from it. The vision is clear: a simple blood test, repeated over time, means more targeted care, fewer unnecessary side effects, and a better chance of not just living longer, but living well.