Plasma ctDNA detects minimal residual disease (MRD) and is associated with disease recurrence in curatively treated CRC. In a randomised, double-blinded, phase III study (The ASpirin for Dukes C and high risk Dukes B COLorecTal cancer trial [ASCOLT], NCT00565708) evaluating the benefit of adjuvant aspirin, pts in the Australian and New Zealand cohort underwent prospective collection of plasma at baseline (within 90 days of completing adjuvant chemotherapy), 6 and 12 months, as well as surgical specimens. In a pilot cohort of 51 pts, we studied the utility of an ultra-sensitive ctDNA assay (SafeSEQ, Sysmex Inostics) for MRD detection. Cell-free DNA (cfDNA) analysis used the SafeSEQ CRC MRD assay (14 genes, AKT1, APC, BRAF, CTNNB1, ERBB3, FBXW7, KRAS, NRAS, PIK3CA, POLE, PPP2R1A, RNF43, SMAD4 and TP53). cfDNA results were correlated with recurrence data and tumour sequencing results using a 59-gene custom panel. All pts (26 female; median age 69; 16 high risk stage II, 35 III) received adjuvant 5-Fluorouracil based chemotherapy (32 with oxaliplatin, 4 had neoadjuvant chemoradiation for rectal cancer) and median follow-up was 60 months. 133 plasma samples were analysed (median 3.8 mL and DNA 71.0 genomic equivalents/ μL). Of the 10 pts with known recurrences (median time to recurrence 19 months), 6 had detectable cfDNA, including 2 of 3 pts without detectable tumour mutations (Table); median time from positive cfDNA to imaging detected recurrence was 28 weeks. Four pts with known recurrence did not have detectable cfDNA, including 1 who recurred 59 months after enrolment. Fourteen pts had plasma mutations without known recurrence. Matched peripheral blood mononuclear cell analyses are awaited.Table: 380PcfDNA mutationsMutant allele fraction (%, 1st sample if multiple)cfDNA detected at baselineAt 6mAt 12mConcordant mutation in tumourTime from positive cfDNA to recurrence on CT (w)Time from enrolment to recurrence (w)CEA elevated at CT recurrenceRecurrence site(s)BRAF V600ETP53 C275Y13.20.05Y- (Not done)-YN05YLiverSMAD4 R496C0.08NNYN4799YLiver, new primarynoneNNN257NPeritoneumKRAS G12VTP53 I195STP53 V272M0.040.160.04NYNYYYYYNYNN101101NLungKRAS G13DSMAD4 540PAPC R1399fs*9TP53 R342*8.42.42.56.5NNNNNNNNYYYYYYNN048NLung, nodalnoneNNN80NLung, nodalTP53 Y220C0.03-Y-N7198YNodal, localKRAS G12VTP53 R306*0.040.07NYYN-YN024NLungnoneNN-30NLungnoneNNN87NLung Open table in a new tab In 51 ASCOLT pts with high risk resected CRC following adjuvant chemotherapy, 6 of 10 with reported recurrences had detectable cfDNA using a tumour naïve SafeSEQ assay. Analyses in the larger cohort (n = 368) are underway.
Read full abstract