The 'liquid biopsy' can be used to choose effective drug treatment options for men with advanced prostate cancer, as well as to monitor drug resistance, according to the study published in Cancer Discovery.
'Our study identifies, for the first time, genetic changes that allow prostate cancer cells to become resistant to the precision medicine olaparib,' said Professor Johann de Bono, from the Institute of Cancer Research (ICR), London. 'From these findings, we were able to develop a powerful, three-in-one test that could in future be used to help doctors select treatment, check whether it is working and monitor the cancer in the longer term.'
The scientists monitored DNA released by prostate cancer cells in regular blood samples taken from 49 men with advanced prostate cancer. The men were enrolled in a clinical trial of the targeted cancer drug, olaparib.
After eight weeks of treatment, tumour DNA levels had halved in the blood of patients who responded to olaparib. In contrast, DNA levels rose by two percent on average in those who did not respond to the drug. Men who had a greater than 50 percent drop in tumour DNA after eight weeks of treatment also survived longer.
Dr Áine McCarthy at Cancer Research UK said the blood test was an important development with the 'potential to greatly improve survival for the disease'.
The researchers also investigated why some men stopped responding to olaparib. It belongs to a class of drugs called PARP-inhibitors that help kill cancer cells with mutation in genes involved in DNA repair, such as BRCA1 and BRCA2. By closely analysing the tumour DNA, they found new genetic changes that cancelled out the original mutations, causing the drug to become ineffective.
Professor Paul Workman, chief executive and president of ICR, said that the test could 'usher in a new era of precision medicine for prostate cancer' and that 'blood tests for cancer promise to be truly revolutionary'. He added that because the tests are cheap, simple to use and non-invasive they could potentially be used to monitor patients early on in treatment.
The blood test is still in early clinical trials involving small numbers of patients, but the researchers are hopeful that the test will help provide greater targeted treatment for patients with fewer side effects.
'Not only could the test have a major impact on treatment of prostate cancer, but it could also be adapted to open up the possibility of precision medicine to patients with other types of cancer as well, ' Professor de Bono concluded.