A plasma-only integrated genomic and epigenomic circulating tumor DNA (ctDNA) assay to inform recurrence risk in colorectal cancer (CRC).

Abstract

3602 Background: ctDNA identifies patients (pts) at high risk for disease recurrence post CRC resection (post-op). Current ctDNA residual disease detection approaches assess only genomic alterations (alts) and rely on tissue sequencing to identify tumor-derived alts. We evaluated a plasma-only ctDNA assay to identify high risk pts. Methods: 72 CRC pts (surgery only = 42; adjuvant therapy (adj) = 30) had post-op and/or post-adj plasma samples (3-4mL). Extracted cfDNA (median 27 ng) was analyzed using a single-sample NGS test validated in early stage CRC that integrates assessment of genomic alts with epigenomic cancer signature (Guardant Health, CA). A variant classifier was applied to differentiate tumor-derived from non-tumor derived alts in a tumor tissue-uninformed approach. Results: In the surgery cohort, samples were collected a median of 31 days (d) post-op. 7/8 pts with post-op ctDNA detected (ctDNA+) recurred (PPV 88%; median time to recurrence (mTTR) 248d). The recurrence-free pt has < 180d follow-up. 7/34 pts without ctDNA detected (ctDNA-) recurred (NPV 79%; mTTR 333d). 1/1 Stage 0-II ctDNA+ pt recurred (PPV 100%; TTR 440d) while 1/20 ctDNA- recurred (NPV 95%; TTR 440d). 27 pts in the adj cohort had samples collected a median of 37d post-adj. 6/6 ctDNA+ pts recurred (PPV 100%, mTTR 239d). 4/21 ctDNA- pts recurred (NPV 81%, mTTR 466d). 2/2 ctDNA+ and 0/11 ctDNA- Stage III pts recurred (PPV, NPV 100%, mTTR 420d). All 3 post-op ctDNA+/post-adj ctDNA+ (ctDNA persistence) pts recurred. 1/2 post-op ctDNA+/post-adj ctDNA- (ctDNA clearance) pts is recurrence free (306d). 2 post-op ctDNA-/post-adj ctDNA+ pts recurred. In the entire cohort, ctDNA+ after standard therapy completion had a recurrence PPV 93%, NPV 80%, HR 11.29 (p < 0.0001). Conclusions: In post-op CRC, ctDNA detection utilizing a tumor-uninformed integrated genomic and epigenomic assay has high recurrence PPV and NPV following standard therapy completion. ctDNA identifies pts who may benefit from post-op adj therapy or additional/modified post-adj therapy. These findings demonstrate that ctDNA detection from a single post-op/post-adj plasma sample stratifies high/low risk pts and informs therapy decision making.