A group of researchers recently discovered that tumor DNA in the blood of a cancer patient can help track the disease as it evolves and develops in real time.

Recovered cancer patients and those in danger of relapsing can benefit from a simple blood test which researchers say is even more effective at analyzing cancer cell behavior than tissue biopsies.

In a study issued in the journal Nature Communications, researchers at the University of Cambridge monitored the condition of a 42-year-old woman with metastatic breast cancer for over three years. After comparing blood samples and surgical tumor samples from the woman, they examined small DNA fragments of the dying tumor cells.

Dr. Sarah-Jane Dawson, one of the researchers of the study, said that everyone had small fragments of DNA in their bloodstream, but that cancer patients had higher levels because the ability of the tumor to shed itself on the bloodstream. She said that searching for tumor DNA in the plasma was like looking for a needle in a haystack.

Researchers then found that liquid biopsies were accurate and had reflected the changes in the patient's tumors as time passed.

"We think we'll be able to use this information to understand how well patients are responding to therapy and, if they're not, try and predict what therapies might be better for that particular individual," said Dawson.

Professor Carlos Caldas, the lead author of the study, believes that their findings will change the way doctors monitor cancer patients, especially because surgical biopsies are often invasive procedures.

"We now need to see if this works in more patients and other cancer types, but this is an exciting first step," said Caldas.

Dr. Keith Stewart, an oncologist from Mayo Clinic's Center for Individualized Medicine, said that he is confident that liquid biopsies will be a routine part of clinical practice in cancer.

Different companies are also now working on liquid biopsies for cancer, and experts from investment bank PiperJaffray say that the U.S. market may even reach US$29 billion annually.

Meanwhile, Cambridge researchers hope that further studies will prove that liquid biopsies would work for a wide range of cancer patients, not just those with breast cancer. They hope that the test will be available within five years.