P-273 - Concordance of RAS mutation status in CRC patients by comparison of results from circulating tumour DNA and tissue-based testing

Date 04 July 2015
Event WorldGI 2015
Session Posters
Topics Colon Cancer
Rectal Cancer
Pathology/Molecular Biology
Translational Research
Presenter R. Scott
Citation Annals of Oncology (2015) 26 (suppl_4): 1-100. 10.1093/annonc/mdv233
Authors R. Scott1, S. Dooley1, W. Lewis2, C. Meldrum3, P. Pockney4, B. Draganic4, S. Smith4, F. Jones5, C. Hewitt6, H. Phillimore1, A. Lucas1, E. Shi1, K. Namdarian1, T. Chan7, D. Acosta1, S.-. Chan1, S. Fox1
  • 1University of Newcastle, Newcastle/AU
  • 2Pathology North, Newcastle/AU
  • 3New South Wales Pathology, Newcastle/AU
  • 4John Hunter Hospital, Newcastle/AU
  • 5Sysmex Inostics Inc., Mundelein/US
  • 6Peter MacCallum Cancer Center, Melbourne/AU
  • 7Peter MacCallum Cancer Institute, Melbourne/AU

Abstract

Introduction

Recent evidence from clinical phase III trials demonstrates superior overall survival for RAS wild-type metastatic colorectal cancer (mCRC) patients vs. RAS mutant mCRC patients when treated in first-line with EGFR antibodies. Full RAS analysis should therefore be performed for all newly diagnosed patients with CRC. A sensitive and comprehensive blood-based RAS mutation test with rapid turn-around-time would greatly benefit clinical practice for accurate and timely stratification of mCRC patients in assessing eligibility for anti-EGFR therapy. Moreover, use of a sensitive blood-based RAS test is particularly advantageous in the metastatic setting, where the tumour sample used for RAS testing may not represent the current mutational status of the patient's disease. For instance, in patients exhibiting extensive tumour heterogeneity, a comprehensive surveying of RAS status by testing multiple tissue samples may neither be practical or feasible. In these situations, a real-time systemic examination of RAS mutational status would be particularly advantageous to make timely decisions for a patient's eligibility for targeted anti-EGFR therapy.

Methods

To examine the efficacy of blood-based vs. tissue-based RAS mutation testing, we compared RAS mutation status by testing of plasma from CRC patients using the OncoBEAMTM 33 mutation RAS panel (Sysmex Inostics) versus standard-of-care RAS testing by Sanger and pyrosequencing of FFPE tumour samples. The study was directed at determining the concordance between plasma and tissue-based RAS testing in CRC patients having advanced disease (i.e. stage IV, or stage III disease with documented multiple lymph node involvement). Patients having a history of another malignancy or having received previous targeted anti-EGFR antibody therapy were excluded. Samples from thirty-five (35) patients met these eligibility criteria; tissue was obtained from either metastatic (in 62% of cases) or from primary colorectal tumour sites (in 38% of cases) and matched temporally to a corresponding plasma sample.

Results

Results were generated for 31 out of 35 paired samples. The remaining four (4) samples are currently being subjected to repeat RAS testing. Overall, results from OncoBEAMTM testing of plasma samples showed a high degree of concordance (93.5%) with 29 out of 31 cases showing equivalent RAS mutational status compared with tumour tissue, 16 out of 18 cases showing positive agreement (89%), and 13 out of 13 showing negative agreement (100%). Moreover, the RAS mutational frequency detected by plasma testing (53%) was not significantly different from that obtained by tumour tissue testing (58%); both values compare favorably with the known frequency of extended RAS mutations observed in CRC patient populations.

Conclusion

Blood-based testing using the OncoBEAMTM 33 mutation RAS digital PCR assay compares favorably with standard-of-care tissue-based RAS mutation testing and may more accurately reflect current RAS mutational status to accurately stratify patients for anti-EGFR therapy. Taken together, these findings support the conclusion that blood-based RAS mutation testing is an appropriate surrogate for tissue-based testing and enables systemic disease assessment and timely decision-making in determining eligibility of mCRC patients for anti-EGFR therapy.