These changes can give an early warning of the cancer becoming resistant to treatment, which can result in a dormant cancer re-emerging.
'Being able to spot the first signs of relapse, so we can rapidly decide the best treatment strategy, is an important area for research,' said lead study author Professor Richard Marais. 'Using our technique we hope that one day we will be able to spot when a patient's disease is coming back at the earliest point and start treatment against this much sooner.'
The study at the Cancer Research UK Manchester Institute examined 364 blood and tumour samples from 214 patients to develop a non-invasive way to track genetic changes in skin cancer cells, using DNA from blood samples.
They showed that the test picked up the emergence of drug-resistant cancer cells and the subsequent re-emergence of cancer before standard clinical examinations. Tracking these changes could allow doctors to tailor treatment to individual skin cancer cases, and the faster the changes are detected the more quickly treatments can be altered to keep skin cancer under control.
Malignant melanoma is an aggressive type of skin cancer and is the fifth most common cancer in Britain. Around 15,000 people are diagnosed every year in the UK, and once the cancer progresses to malignancy it is often fatal.
The progression of the disease varies from patient to patient, depending on which genetic changes are present in cancer cells. Around half of melanoma patients have cancer cells with a genetic change in the BRAF gene, which means they can be treated with recently developed targeted drugs like vemurafenib. However, some patients' tumours develop resistance to these drugs after a relatively short time. When this happens, these patients can be offered different immunotherapy drugs that the cancer is still susceptible to.
Researchers said that detecting this resistance early could be key to improving patient care and survival.
Professor Peter Johnson, Cancer Research UK's chief clinician, said: 'One of the sinister things about melanoma is that it can lay dormant for years and then suddenly re-emerge, probably as it escapes from the control of the body's immune system. Being able to track cancers in real time as they evolve following treatment has huge potential for the way we monitor cancers and intervene to stop them growing back.
'There's still some time until we see this in the clinic but we hope that in the future, blood tests like these will help us to stay one step ahead in treating cancer.'