Clinical implementation of expanded RAS testing has been shown to improve the identification of mCRC patients for treatment with anti-EGFR therapy. Historically, tumour tissue has been the preferred sample type. However, emerging evidence suggest that single site tissue biopsies may not account for features of tumour molecular heterogeneity in the metastatic setting. Numerous retrospective studies support the value of blood-based RAS testing for therapy selection and monitoring. The aim of the present study was to test 100 prospectively collected samples to evaluate whether plasma testing with BEAMing is a viable alternative to standard of care tumour FFPE testing for determining RAS mutation status of mCRC patients.
Peripheral blood was collected in Streck cell-free DNA BCT® tubes from an initial cohort of 43 mCRC patients that were either newly-diagnosed (72%) or presented with recurrent disease (28%). Circulating cell-free DNA was extracted and used for RAS mutation analysis using the OncoBEAM® RAS CRC assay at Sysmex Inostics. Results were then compared to those obtained by sequencing of KRAS and NRAS genes in DNA extracted from FFPE tumour tissue from the same patients. Discordant cases were re-examined with BEAMing of DNA derived from FFPE samples when available.
The overall agreement of plasma and tissue RAS mutation testing was 93% (40/43 patients), with positive percent agreement of 91.7% (22/24), and negative percent agreement of 94.7% (18/19). Re-examination of tissue from 1 case by BEAMing revealed a RAS mutation that matched the result obtained in plasma. RAS mutations were detected in 53.3% of plasma and 55.8% of tissue samples, respectively, similar to the expected prevalence of RAS mutations in mCRC patients.
In this first prospective RAS mutation concordance study, a high overall agreement was observed between results obtained from tissue and plasma samples. These results are comparable to those obtained in retrospective studies. Overall, these findings indicate that RAS testing of plasma using BEAMing is a viable alternative to tissue RAS testing for determining mCRC patient eligibility for anti-EGFR therapy.
Clinical trial identification
Legal entity responsible for the study
D. Edelstein, F.S. Jones: Employee of Sysmex Inostics, Inc. P. Ronga: Employee of Merck KGaA, Damstadt, Germany. A. Telaranta-Keerie: Was an employee of Sysmex Inostics, Inc. All other authors have declared no conflicts of interest.