The study by Diehl et al. explores the use of circulating tumor DNA (ctDNA) as a biomarker to monitor tumor dynamics in patients with colorectal cancer. The researchers developed a highly sensitive method, modified BEAMing, to quantify ctDNA in plasma samples from 18 subjects undergoing multimodality therapy. They found that ctDNA levels could reliably reflect tumor burden and predict recurrence, with a median decrease of 99.0% in ctDNA after complete surgical resection. This approach was more sensitive and specific than the standard biomarker, carcinoembryonic antigen (CEA), which showed a less marked decrease in response to surgery. The study suggests that ctDNA could be a valuable tool for noninvasive monitoring of cancer progression and guiding treatment decisions, similar to the use of viral nucleic acids in HIV management.The study by Diehl et al. explores the use of circulating tumor DNA (ctDNA) as a biomarker to monitor tumor dynamics in patients with colorectal cancer. The researchers developed a highly sensitive method, modified BEAMing, to quantify ctDNA in plasma samples from 18 subjects undergoing multimodality therapy. They found that ctDNA levels could reliably reflect tumor burden and predict recurrence, with a median decrease of 99.0% in ctDNA after complete surgical resection. This approach was more sensitive and specific than the standard biomarker, carcinoembryonic antigen (CEA), which showed a less marked decrease in response to surgery. The study suggests that ctDNA could be a valuable tool for noninvasive monitoring of cancer progression and guiding treatment decisions, similar to the use of viral nucleic acids in HIV management.