Blood test could help personalise treatment for advanced prostate cancer

Scientists have developed a blood test that could help doctors select the best treatment for men with aggressive prostate cancer.

The multipurpose test could also help monitor patients to see if a particular type of treatment is working, according to the study published in the journal Cancer Discovery. 

Scientists at The Institute of Cancer Research, London and The Royal Marsden NHS foundation Trust studied DNA released by prostate cancer cells in to the bloodstream of 46 men with prostate cancer that had spread. 

The men were taking part in a phase 2 clinical trial where they were treated with olaparib (Lynparza), a targeted cancer drug called a PARP inhibitor. Regular blood samples were taken after treatment had started, and the researchers measured the amount of tumour DNA present in the blood.

In blood samples taken 8 weeks after treatment, tumour DNA levels had halved on average in the 16 patients whose tumours shrank to some degree with olaparib. In the 30 patients whose tumours didn’t respond, DNA levels were on average 2% higher 8 weeks after treatment.

Men whose blood samples showed a 50% or greater drop in tumour DNA 8 weeks after treatment survived longer.

Olaparib can target cancer cells with a faulty BRCA gene because the cells become reliant on the PARP molecule to repair damage to their DNA. But tumours can become resistant to the drug.

By analysing the tumour DNA in blood samples from a small number of men closely, the researchers were also able to uncover genetic faults that might explain why treatment stopped working.

They believe the new faults ‘cancel out’ the original ones, rendering the drug ineffective.

Professor Johann de Bono, Medical Oncologist at The Royal Marsden NHS Foundation Trust, who led the research said: “Our study identifies, for the first time, genetic changes that allow prostate cancer cells to become resistant to the precision medicine olaparib.” 

He believes the test could “help doctors select treatment, check whether it is working and monitor the cancer in the longer term. We think it could be used to make clinical decisions about whether a PARP inhibitor is working within as little as four to eight weeks of starting therapy”.

Dr Áine McCarthy, senior science information officer at Cancer Research UK, agreed that the development of the blood test was important.

“The test has the potential to greatly improve survival for the disease by ensuring patients get the right treatment for them at the right time, and that they aren’t being given a treatment that’s no longer working,” she said.

In the future, the researchers believe the test could be used both before and after treatment.

The team is calling the new test a ‘three-in-one blood test’ because they believe it could:

• Identify patients who are likely to benefit from olaparib based on genetic faults found in tumour DNA blood samples
• Monitor patients during treatment to look for early signs that treatment is working or not
• Potentially spot why treatment stops working so decisions around switching treatment can be made sooner 

Cancer Research UK’s Dr McCarthy added: “Further studies involving a larger group of men will confirm if doctors should use this test when treating patients with advanced prostate cancer.”