Digital PCR test for metastatic colorectal cancer studied

Aug. 27, 2020

Sysmex Inostics, which specializes in blood-based circulating tumor DNA (ctDNA) analysis for oncology, announced the publication of a clinical study evaluating RAS mutation status in circulating tumor DNA (ctDNA) of colorectal cancer (CRC) patients undergoing anti-EGFR antibody therapy (cetuximab or panitumumab) rechallenge using the OncoBEAM RAS CRC test in two different multicenter Japanese retrospective trials, JACCRO CC-08 and JACCRO CC-09, according to a press release from the company.

OncoBEAM RAS CRC is a test that uses BEAMing technology, an enhanced digital PCR method optimized for high-sensitivity blood-based mutation detection for metastatic colorectal cancer (mCRC) patients. In this study, investigators utilized the highly sensitive nature of OncoBEAM testing to explore the clinical value of monitoring changes in plasma RAS mutations in CRC patients during treatment with anti-EGFR antibody therapy.

Treatment of mCRC patients with anti-EGFR monoclonal antibodies have demonstrated significant improvements in the survival of patients with wild-type RAS tumors. mCRC patients being considered for anti-EGFR therapy rechallenge could greatly benefit the overall patient survival by undergoing initial plasma testing to establish RAS mutation status at baseline, as well as performing subsequent tests to monitor RAS mutation dynamics during treatment. By receiving regular blood draws throughout the anti-EGFR rechallenge treatment, patients would benefit from periodic OncoBEAM RAS testing, which would deliver valuable insights for clinicians in assessing therapy response.

The study, which was was published in JCO Precision Oncology, demonstrated that RAS mutations were found in 38 percent of CRC patients after receiving the first course of anti-EGFR mAb therapy, but prior to rechallenge treatment. The disease control rate (DCR) was 33 percent in patients with RAS mutations in ctDNA, whereas it was 80 percent in patients without RAS mutation detected by OncoBEAM at baseline.

The data also showed that patients with RAS mutations detected just before anti- EGFR mAb rechallenge had no survival benefit from rechallenge treatment. Moreover, post-progression survival time after rechallenge was worse in patients with RAS mutations than in patients without mutations at disease progression. The emergence of RAS mutations during rechallenge treatment at disease progression is, therefore, useful for predicting outcomes of anti- EGFR mAb therapy rechallenge.

Besides results of this publication, a new prospective observational trial "REMARRY (UMIN000036424)" has been initiated with over 100 patients recruited as of June 2020. This clinical trial, supported by SCRUM-Japan MONSTAR-SCREEN, will expand the evaluation of patient-specific dynamics in ctDNA RAS mutational status as a predictor of anti-EGFR mAb rechallenge efficacy.

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