The study presents a method for quantifying circulating tumor DNA (ctDNA) in plasma samples from patients with colorectal cancer to monitor tumor dynamics. Using a highly sensitive technique called BEAMing, researchers quantified ctDNA in 162 plasma samples from 18 subjects undergoing multimodal therapy. They found that ctDNA levels could reliably track tumor burden during surgery and chemotherapy. ctDNA measurements showed a sharp decrease after complete resection, while incomplete resections led to variable changes, sometimes with increases due to residual tumor tissue injury. ctDNA levels were also correlated with tumor volume and recurrence rates, outperforming the standard biomarker CEA in sensitivity and predictive accuracy. The study highlights the potential of ctDNA as a personalized biomarker for cancer monitoring, offering a non-invasive method to assess tumor dynamics and guide treatment decisions. The approach is considered a form of personalized genomics, with the advantage of high specificity but requiring individual mutation identification. The study also suggests that ctDNA levels reflect systemic tumor burden, though the exact proportion remains uncertain. The findings support the use of ctDNA in cancer management, with potential applications in screening and monitoring. The study was conducted with ethical approval and involved rigorous statistical analysis to validate results. The method is promising for future cancer diagnostics and personalized treatment strategies.The study presents a method for quantifying circulating tumor DNA (ctDNA) in plasma samples from patients with colorectal cancer to monitor tumor dynamics. Using a highly sensitive technique called BEAMing, researchers quantified ctDNA in 162 plasma samples from 18 subjects undergoing multimodal therapy. They found that ctDNA levels could reliably track tumor burden during surgery and chemotherapy. ctDNA measurements showed a sharp decrease after complete resection, while incomplete resections led to variable changes, sometimes with increases due to residual tumor tissue injury. ctDNA levels were also correlated with tumor volume and recurrence rates, outperforming the standard biomarker CEA in sensitivity and predictive accuracy. The study highlights the potential of ctDNA as a personalized biomarker for cancer monitoring, offering a non-invasive method to assess tumor dynamics and guide treatment decisions. The approach is considered a form of personalized genomics, with the advantage of high specificity but requiring individual mutation identification. The study also suggests that ctDNA levels reflect systemic tumor burden, though the exact proportion remains uncertain. The findings support the use of ctDNA in cancer management, with potential applications in screening and monitoring. The study was conducted with ethical approval and involved rigorous statistical analysis to validate results. The method is promising for future cancer diagnostics and personalized treatment strategies.