Abstract 380P
Background
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.
Methods
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.
Results
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: 380P
| cfDNA mutations | Mutant allele fraction (%, 1st sample if multiple) | cfDNA detected at baseline | At 6m | At 12m | Concordant mutation in tumour | Time from positive cfDNA to recurrence on CT (w) | Time from enrolment to recurrence (w) | CEA elevated at CT recurrence | Recurrence site(s) |
| BRAF V600E TP53 C275Y | 13.20.05 | Y | - (Not done) | - | YN | 0 | 5 | Y | Liver |
| SMAD4 R496C | 0.08 | N | N | Y | N | 47 | 99 | Y | Liver, new primary |
| none | N | N | N | 257 | N | Peritoneum | |||
| KRAS G12V TP53 I195S TP53 V272M | 0.040.160.04 | NYN | YYY | YYN | YNN | 101 | 101 | N | Lung |
| KRAS G13D SMAD4 540P APC R1399fs*9 TP53 R342* | 8.42.42.56.5 | NNNN | NNNN | YYYY | YYNN | 0 | 48 | N | Lung, nodal |
| none | N | N | N | 80 | N | Lung, nodal | |||
| TP53 Y220C | 0.03 | - | Y | - | N | 71 | 98 | Y | Nodal, local |
| KRAS G12V TP53 R306* | 0.040.07 | NY | YN | - | YN | 0 | 24 | N | Lung |
| none | N | N | - | 30 | N | Lung | |||
| none | N | N | N | 87 | N | Lung |
Conclusions
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.
Clinical trial identification
NCT00565708.
Editorial acknowledgement
Legal entity responsible for the study
National Cancer Centre Singapore for the overall ASCOLT study, AGITG/ NHMRC Clinical Trials Centre, University of Sydney for Australia and New Zealand sites.
Funding
Australasian Gastro-Intestinal Trials Group (AGITG) for funding the study and the Royal Australasian College of Physicians for stipend support for D. Day.
Disclosure
A. Starus: Other, Institutional, Full or part-time Employment: Sysmex Inostics, Inc. A. Lamik: Other, Institutional, Full or part-time Employment: Sysmex Inostics. F. Jones: Other, Institutional, Full or part-time Employment: Sysmex Inostics, Inc. All other authors have declared no conflicts of interest.