Analysing fragments of DNA that are shed by tumours into the bloodstream, could indicate early on whether patients are at risk of their cancer spreading, according to new research.

Researchers at The Royal Marsden NHS Foundation Trust say ctDNA, a form of liquid biopsy, may be an accurate technique to monitor treatment response in patients with locally advanced rectal cancer, allowing treatment to be adapted or changed earlier to try to prevent the development of metastatic disease.

Results from the study have been presented at the EACR-ESMO joint conference on liquid biopsies.

Researchers analysed liquid biopsies from 47 patients at The Royal Marsden who had localised rectal cancer - i.e. cancer that had not already spread to other body parts.

They took blood samples before, during and after patients had completed treatment with combined chemotherapy and radiotherapy (CRT), and after surgery.

They were able to detect ctDNA in 74 percent of patients pre-treatment, 21 percent of patients mid-way through CRT, 21 percent after CRT and 13 percent after surgery.

The ctDNA results at the end of CRT were associated with tumour response to CRT as shown on MRI scans.

With a median follow up of just over 2 years, they found ctDNA results to be consistent with occurrences of cancer spreading outside of the rectum; patients with ctDNA persisting throughout their treatment, were more likely to develop metastatic disease sooner.

Lead author Dr Shelize Khakoo, Medical Oncologist at The Royal Marsden NHS Foundation Trust said: "We know patients respond quite differently to standard treatment - some will do really well, and have what we call a complete pathological response. For others, the cancer may spread during treatment.

"If we can predict early on who will go on to develop metastatic disease, we might be able to tailor treatment by making it more intense or trying an alternative."

Co-lead author Professor David Cunningham OBE, Consultant Medical Oncologist at The Royal Marsden NHS Foundation Trust said: 'These results suggest that liquid biopsies offer us an accurate method of establishing the cancer's activity throughout the body.

"Importantly what this study showed, which has not yet been explored, is that persistence of ctDNA mid-way through treatment could be an early indicator of the cancer's potential to spread. Using this measure, along with MRI scans, we can offer a more personalised treatment approach for patients."

Dr Khakoo added: "Whilst our findings are interesting and exciting, it's important to note that this was carried out in a small cohort of patients and would require further validation in a larger trial."

Source: The Royal Marsden NHS Foundation Trust