Scientists may have taken a step forward in the treatment of cancer by developing a blood test that can identify key genetic mutations driving resistance to a widely used drug.

The test is expected to be used in the prostate cancer treatment, with only those patients whose cancers are free of resistant mutations taking the drug abiraterone.

Gerhard Attard is “delighted to have developed a test that appears to predict very accurately whether a patient will respond to abiraterone, and that it can be performed on blood samples – removing the need to take a biopsy”.

The study, led by Gerhardt Attard, clinician scientist at the Institute of Cancer Research, and consultant medical oncologist at The Royal Marsden NHS Foundation Trust, also shows that tests for cancer DNA in the bloodstream can be used to detect drug resistance mutations – allowing patients who will not benefit from one drug to be given an alternative treatment.

Maltese-born Attard said: “The discovery of abiraterone was an important step forward for patients with advanced prostate cancer, but we know it doesn’t work for all men, and we’ve been searching for a marker that will tell us in advance which men will benefit.

“We’re delighted to have developed a test that appears to predict very accurately whether a patient will respond to abiraterone, and that it can be performed on blood samples – removing the need to take a biopsy.

Researchers at ICR, the Royal Marsden NHS Foundation Trust, and the University of Trento, Italy, analysed 274 blood samples from 97 patients using state-of-the-art DNA sequencing techniques.

They found that mutations in a gene called the androgen receptor (AR) predicted resistance to the prostate cancer drug abiraterone, and that patients with these mutations had poorer survival.

Abiraterone, which was discovered at the ICR, is now standard treatment for men with advanced prostate cancer – but while it is highly effective in many patients, 30-60 per cent do not respond.

Researchers have been looking for a marker that will help predict in advance which men will benefit from the drug, and who should be given a different treatment.

They discovered that men who harbour either a specific mutation or an increase in the number of copies of the AR gene, were 7.8 times less likely to have a reduction of more than 90 per cent in their PSA levels, a widely used test to monitor the response of prostate cancer.

The study also found that in about 15 per cent of men given abiraterone who did not have either mutation before starting treatment, this was acquired as the drug stopped working and appeared in the bloodstream several months before patients developed any symptoms.

Blood tests are valuable in cancer patients because biopsies are often difficult to perform and can carry risks.

Even when biopsies are possible, they only give a snapshot of cancer genetics in a small specific area, whereas blood tests can give information that is more representative of multiple different tumours around the body.

Attard added: “We are now planning a clinical trial involving up to 600 men in which we aim to prospectively show that men who are positive with our test have significantly greater benefit from chemotherapy in preference to abiraterone or similar drugs.

“Critically, we believe that this sort of technology would be relatively straightforward to implement in hospitals, making it accessible to a large number of patients.

“Additionally, looking at tumour DNA in the blood of patients could potentially give us an overall picture of why the cancer is progressing all over the body, unlike a biopsy that only tells us about the area sampled,” explained Attard.

The study is published in the journal Science Translational Medicine.