OncoBEAM RAS CRC kit using BEAMing technology is a circulating tumour DNA (ctDNA) test for detecting plasma RAS mutational status in metastatic colorectal cancer (mCRC). We conducted a multicentre, prospective study to investigate the concordance of the RAS mutational status between plasma ctDNA and tumour tissue DNA.

mCRC patients without prior anti-EGFR antibodies or regorafenib treatment were enroled. Plasma- and tissue-based RAS mutational status were determined by BEAMing, respectively.

A total of 280 patients from eight institutions were eligible. The overall agreement between plasma- and tissue-based analyses was 86.4%, with a positive percent agreement of 82.1% and negative percent agreement of 90.4%. From logistic regression analysis, lung metastasis alone indicated the most significant factor associated with discordance. The agreement between plasma- and tissue-based analyses was 64.5% in patients with lung metastasis alone (n = 31) indicating lower amount of ctDNA. Among the cases with lung metastasis alone, all plasma- and tissue-based analyses were perfectly concordant in cases with ≥20 mm of maximum lesion diameter or ≥10 lesions.

The clinical validity of OncoBEAM RAS CRC kit was confirmed. Careful attention should be paid for mCRC patients with lung metastases alone having fewer metastases or smaller diameter lesions.