Circulating tumor DNA as a prognostic biomarker in metastatic colorectal cancer: Post-hoc analysis of treatment response and survival outcomes in the ALTER-C-002 study

Circulating tumor DNA (ctDNA) derived from blood samples can serve as a minimally invasive, real-time indicator of tumor burden and treatment response in metastatic colorectal cancer. This study evaluated the association between baseline ctDNA levels and changes in ctDNA during treatment with response and survival outcomes in the phase II ALTER-C-002 trial, which investigated first-line anlotinib combined with capecitabine and oxaliplatin in patients with rat sarcoma (RAS) and B-Raf proto-oncogene (BRAF) wild-type metastatic colorectal cancer. In this post-hoc biomarker analysis, plasma samples were collected at baseline, near the best radiologic response (C1), and at the timepoint closest to disease progression or last follow-up (C2). These samples were analyzed using a 90-gene next-generation sequencing (NGS) panel, with ctDNA abundance quantified as maximum somatic allele frequency (MSAF), where MSAF <0.001 indicated ctDNA negativity. Biomarker data were obtained for 26 patients, 25 of whom had measurements at all three timepoints. Notably, baseline MSAF was higher in patients with liver-only metastasis (p=0.017). MSAF decreased significantly at C1 compared to baseline (p<0.001) and increased at C2 relative to C1 in patients exhibiting progressive disease (PD) (p<0.001); additionally, higher MSAF at C1 was associated with subsequent PD at C2 (p=0.015). All patients who tested ctDNA-negative at C1 achieved an objective response, and ctDNA negativity at this timepoint correlated with longer progression-free survival (PFS) (p=0.012) and overall survival (OS) (p=0.006) compared to ctDNA-positive patients. Furthermore, KRAS/BRAF mutations detected in ctDNA were linked to shorter PFS and OS (all p<0.05). In conclusion, baseline ctDNA burden and early ctDNA clearance may function as prognostic and on-treatment biomarkers of therapeutic efficacy in metastatic colorectal cancer, warranting prospective validation.