A simple blood test can help treat children with rhabdomyosarcoma, a new study by scientists at the Institute of Cancer Research in London has found. Detection of cancer DNA in the bloodstream can tell doctors whether the disease has returned or begun to metastasize. Researchers found that blood tests using a so-called liquid biopsy can detect signs of cancer recurrence, assess the severity of the disease and help guide medication choices in children with rhabdomyosarcoma. About three-quarters of patients examined with such blood tests before treatment have been found to have key genetic changes in their disease. And some of these may make a difference in treatment choices. Rhabdomyosarcoma is a rare type of cancer that mostly affects children. Less than a third of young patients with recurrence or metastasis survive. The scientists used blood and tissue samples from 28 young patients with rhabdomyosarcoma. Laboratory mice were also used. The scientists determined whether DNA released by cancer cells into the bloodstream could be used to track the progression and aggressiveness of tumors. And whether it was feasible to use this data in young patients for a faster and less painful biopsy compared to traditional tissue biopsy.