Correlation between the timing of recurrence and circulating tumor DNA (ctDNA) doubling time in patients (pts) with resected colon cancer.

220 Background: Previous studies have demonstrated that persistent ctDNA positivity in pts with colon cancer is associated with significantly worse outcomes compared to persistent ctDNA negativity. However, the association between outcomes and the rate of change in ctDNA levels has yet to be established. Here, we evaluated lead time from ctDNA positivity to recurrence based on rate of ctDNA increase. Methods: Pts with resected stage I-IV colon cancer enrolled in the prospective, observational GALAXY study (UMIN000039205) who had ctDNA testing (Signatera) with ≥2 consecutive ctDNA-positive post-definitive treatment results and clinical relapse information were included (N=164; median 3 timepoints per pt, range 2-7). The rate of change in ctDNA levels (mean tumor molecules/mL) was calculated; a slope of 0.3, corresponding to a 1-month doubling time, was used as a cutoff for fast (≥0.3) and slow (