Simply by analysing a patient's blood, doctors have shown they can identify faulty DNA which indicates how fast a tumour is growing and whether or not their treatment is proving effective.
The low-cost blood test, trialled on ovarian cancer patients, could be used instead of repeat biopsies to monitor the progress of cancer once it has been diagnosed and treatment has begun.
Although the technology is not yet accurate enough to detect early-stage tumours, researchers said it could become a key tool in cancer diagnosis and treatment within five to ten years.
Improvements in understanding how to target specific genetic faults in tumours could improve the effectiveness of the test and allow it to be applied to other cancer types, they added.
The test, developed by researchers from the Cancer Research UK Cambridge Research Institute, picks out fragments of mutated DNA which are leaked into the bloodstream when cancer cells die.
By regularly testing a patient's blood doctors could get a "real time" picture of how a tumour is responding to treatment, with a drop in faulty DNA indicating that the condition is stabilising, and a rise signifying that the patient is relapsing.
The best current method of monitoring a patient's progress is to take a biopsy of their tumour but this is invasive and raises the risk that the sample may give a misleading snapshot of all the genetic mutations in the tumour.
Biopsies are also difficult to carry out once the cancer has spread to other parts of the body.
Although the new method is not as accurate at detecting mutations as a biopsy, it could be used following an initial biopsy to track changes in a patient's condition without the need for further surgery.
Writing in the Science Translational Medicine journal, researchers reported that they had been able to detect genetic faults involved in tumour growth in 20 out of 38 tests on women with a particular subtype of ovarian cancer.
The test was targeted to look for 20,000 possible mutations in DNA from a particular part of the genetic code which is heavily linked to the patients' cancer type, known as high-grade serous ovarian carcinoma.
It marks the first time scientists have successfully screened entire genes in a blood test to identify mutations which developed in the cancer.
By looking at different parts of the genetic code the test could be adapted to suit other cancer types with up to 80 per cent efficiency, researchers said.
They also tracked a breast-cancer patient for 16 months and demonstrated the test could accurately monitor the progression of her tumour.
Dr Nitzan Rosenfield, who led the study, said: "This type of blood test has the potential to revolutionise the way we diagnose and treat cancer. The great advantage is that it can be used to identify cancer mutations without surgery or a biopsy, making it safer and cheaper.
"It is not more effective than biopsy, but it is a different animal. You can do a biopsy once, but you can't take a biopsy every time the patient comes to the clinic."
The Telegraph 30th May 2012