Liquid Biopsy Test Accurately Detects RAS Mutations in Metastatic Colorectal Cancer

The OncoBEAM RAS kit for circulating tumor DNA (ctDNA) analysis of patients with metastatic colorectal cancer (mCRC) demonstrated high positive and negative agreement of RAS mutations detected by tumor tissue analysis, according to data presented at the ESMO World Congress on Gastrointestinal Cancer 2018.¹

The OncoBEAM RAS kit (Sysmex) detects RAS mutations harbored by patients with mCRC using plasma samples or liquid biopsy. The goal of this study was to determine the agreement between the OncoBEAM kit liquid biopsy analysis with archival formalin-fixed and paraffin-embedded tumor tissue analysis.

The study included 280 patients with mCRC not treated with anti-EGFR antibodies or regorafenib from Japan who had archival tissue specimens collected within 5 years. OncoBEAM RAS kit and Tissue OncoBEAM RAS assay were compared using plasma and tumor tissue specimens, respectively. Discordant cases were further tested by plasma next-generation sequencing.

The OncoBEAM RAS kit analysis of plasma samples demonstrated an overall agreement of 86.4% with tumor tissue analysis, with a positive concordance of 82.1% and a negative concordance of 90.4%. The OncoBEAM RAS kit and plasma next-generation sequencing analyses demonstrated a 96% concordance.

There were 38 cases of discordance, with plasma-positive and tissue-negative results in 14 cases and plasma-negative and tissue-positive results in 24 cases. Of the plasma-negative, tissue-positive cases, 10 occurred in patients with lung metastases only. When the cases were stratified by lung metastasis, the concordance between plasma- and tissue-analyses was 64.5% in the group with only lung metastases compared with 89.2% in the group excluding patients with only lung metastases.

The authors stated that the results suggest that the OncoBEAM RAS kit accurately detected RAS mutations among Japanese patients with mCRC. They cautioned, however, that “careful attention should be paid for mCRC patients with lung metastases alone when considering use of plasma ctDNA test instead of tissue-based test.”

Read more of Cancer Therapy Advisor‘s coverage of the ESMO World Congress on Gastrointestinal Cancer 2018 meeting by visiting the conference page.

Reference

1. Kagawa Y, Kato T, Bando H, et al. A m[LB3] ulticentre, prospective clinical evaluation study for analyzing RAS mutational status utilizing plasma circulating tumor DNA in patients with metastatic colorectal cancer. Ann Oncol. 2018;29 (suppl 5;abstr O-005):v101. doi: 10.1093/annonc/mdy149