Abstract 3589: Validation of the role of circulating tumor DNA (ctDNA) in tracking mechanisms of resistance to anti-EGFR monoclonal antibodies (AE-mABs): preliminary results of the PROSPECT-C prospective trial

Abstract

Background: AE-mABs (cetuximab and/or panitumumab) have been approved for the treatment of RAS wild-type (WT) metastatic colorectal cancer (mCRC) patients (pts). Indeed, previous studies have identified mutations (MTs)/amplifications in RAS/RAF/MEK kinase pathway as the main genetic events promoting primary and acquired resistance to these mABs. RAS status is frequently established on archival material, as tumour re-biopsy may not be always feasible. PROSPECT-C is a prospective trial aiming to define novel and known mechanisms of resistance to AE-mABs by obtaining repeated biopsies and sequential bloods from pts receiving AE-mABs for chemo-refractory mCRC. Here we present the preliminary results of the PROSPECT-C liquid biopsy study where the goals were to: 1) confirm the ability of ctDNA to determine RAS status prior to treatment; 2) determine any discordance of RAS status between archival material and ctDNA; 3) confirm the ability of ctDNA to track emerging MTs in the RAS pathway. Materials and Methods: Plasma was collected at baseline (BL), every 4 weeks and at progression (PD). ctDNA was isolated using the QIAamp Circulating Nucleic Acid Kit (Qiagen) and analyzed by digital droplet PCR (QX200 Bio-Rad) for MTs in KRAS-G12D, KRAS-G13D, KRAS-G12V, KRAS-Q61HA>T, KRAS-Q61HA>C, and BRAF-V600E. In the next steps, plasma samples with no MTs in the first series of hotspots will be tested for the remaining KRAS hotspots, NRAS, EGFR, PIK3CA MTs and KRAS, c-MET and HER-2 amplifications (Data to be presented). Results: Twenty-four pts (all treated with AE-mAB monotherapy) with KRAS WT tumors (from archival tissue) have been treated on this ongoing study; 16/24 had ctDNA analysis (mean age 62 years, 62.5% males) so far. All pts were heavily pre-treated; 58.3%, 31.3% and 12.5% received 2, 3 and 4 lines of prior therapies respectively. Of 15 pts with BL samples, 5 had MTs at BL; 2 with KRAS-G12D, 1 with KRAS Q61HA>T and 2 pts with BRAF-V600E (in the latter case concordance was found with the archival material). Best response was found to be PD in 4/5 pts and stable disease in 1/5pt with BL MTs; 2 with BRAF MTs progressed in <2 months (mo). The median progression free survival (PFS) for pts with BL MTs was 1.8 mo. Five pts with no MT at BL developed one or more MTs later; those included 4 with KRAS-G12D, 3 with KRAS-G13D and 2 with KRASQ61HA>T (median PFS = 4.8 mo). 3/15 (20%) pts showed discordance in RAS MTs between archival material (WT) and baseline bloods (MT); all of them progressed within 3 mo. Conclusions: Liquid biopsies can be a useful tool in determining and tracking RAS MTs in pts undergoing anti-EGFR therapy for mCRC. ctDNA analysis to assess RAS mutational status prior to receiving AE-mABs in our series showed 20% discordance between the archival solid and BL liquid biopsies, which may account for resistance to these therapies. Citation Format: Khurum Khan, George Vlachogianis, David Cunningham, Jens Hahne, Mahnaz Darvish-Damavandi, Sarah Barton, Francesco Trevisani, Giulia Mentrast, Clare Peckitt, Andrea Lampis, Chiara Braconi, Nasir Khan, Ruwaida Begum, Naureen Starling, Sheela Rao, David Watkins, Annette Bryant, Ian Chau, Nicola Valeri. Validation of the role of circulating tumor DNA (ctDNA) in tracking mechanisms of resistance to anti-EGFR monoclonal antibodies (AE-mABs): preliminary results of the PROSPECT-C prospective trial. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3589. doi:10.1158/1538-7445.AM2015-3589

Next generation sequencing identifies ‘interactome’ signatures in relapsed and refractory metastatic colorectal cancer

“…NGS enhances elucidation of tumor clonal evolution and pathway-network analysis elaborating new and anticipated drug resistance mechanisms. The PROSPECT-C, reported that obtaining circulating tumor DNA of a patient with mCRC while on cetuximab therapy revealed a compensatory rise and fall in mutant RAS clones in response to the presence or absence of anti-EGFR therapy (38). As reported earlier within our cohort of pts, NGS data from new liver metastasis was obtained in a patient with RAS wild-type mCRC heavily pretreated with chemotherapy, anti-VEGF therapy and anti-EGFR therapy that subsequently developed coexistent KRAS (Q61L) plus NRAS (Q61H) mutations.…”