They said that “liquid biopsies” analysing tumour DNA circulating in the blood could give an accurate picture of cancer development in individual patients, so treatment could be better targeted.
The study, published in in Science Translational Medicine, used complex genetic analysis of biopsies and blood samples from patients with advanced prostate cancer.
In several patients, use of glucocorticoids coincided with the emergence of androgen receptor mutations and the progression of cancer into more advanced forms.
The study showed that blood tests to measure circulating tumour DNA levels – which is less expensive and invasive than taking repeated samples of tumours with needle biopsies – could be used to monitor the emergence of treatment-resistant prostate cancer.
Study leader Dr Gerhardt Attard, Cancer Research UK Clinician Scientist at The Institute of Cancer Research, London, said: “Our study showed that a steroid treatment given to patients with advanced prostate cancer and often initially very effective started to activate harmful mutations and coincided with the cancer starting to grow again.”
Professor Paul Workman, Interim Chief Executive at The Institute of Cancer Research, London, said: “Drug resistance is the single biggest challenge we face in cancer research and treatment, and we are just beginning to understand how its development is driven by evolutionary pressures on tumours.
“This important discovery reveals how some cancer treatments can actually favour the survival of the nastiest cancer cells, and sets out the rationale for repeated monitoring of patients using blood tests, in order to track and intervene in the evolution of their cancers.”
Dr Matthew Hobbs, Deputy Director of Research at Prostate Cancer UK, said: “There are currently too few treatment options for men living with advanced stage prostate cancer. Not only do we desperately need to find more treatments for this group of men, we also need to understand more about when those that are available stop working and why.”
He said the research was important because it could help to pinpoint the stage at which some drugs stop being effective.
“In the future this could arm doctors with the knowledge they need to ensure that no time is wasted between a drug that stops working for a man and him moving on to another effective treatment,” he said.
However he cautioned that the study was an early piece of research, carried out in very few men, with larger studies needed.