Concordance of blood- and tumor-based detection of RAS mutations to guide anti-EGFR therapy in metastatic colorectal cancer

Abstract

BackgroundCirculating tumor DNA (ctDNA) is a potential source for tumor genome analysis. We explored the concordance between the mutational status of RAS in tumor tissue and ctDNA in metastatic colorectal cancer (mCRC) patients to establish eligibility for anti-epidermal growth factor receptor (EGFR) therapy.Patients and methodsA prospective-retrospective cohort study was carried out. Tumor tissue from 146 mCRC patients was tested for RAS status with standard of care (SoC) PCR techniques, and Digital PCR (BEAMing) was used both in plasma and tumor tissue.ResultsctDNA BEAMing RAS testing showed 89.7% agreement with SoC (Kappa index 0.80; 95% CI 0.71 − 0.90) and BEAMing in tissue showed 90.9% agreement with SoC (Kappa index 0.83; 95% CI 0.74 − 0.92). Fifteen cases (10.3%) showed discordant tissue-plasma results. ctDNA analysis identified nine cases of low frequency RAS mutations that were not detected in tissue, possibly due to technical sensitivity or heterogeneity. In six cases, RAS mutations were not detected in plasma, potentially explained by low tumor burden or ctDNA shedding. Prediction of treatment benefit in patients receiving anti-EGFR plus irinotecan in second- or third-line was equivalent if tested with SoC PCR and ctDNA. Forty-eight percent of the patients showed mutant allele fractions in plasma below 1%.ConclusionsPlasma RAS determination showed high overall agreement and captured a mCRC population responsive to anti-EGFR therapy with the same predictive level as SoC tissue testing. The feasibility and practicality of ctDNA analysis may translate into an alternative tool for anti-EGFR treatment selection.

Temporal and spatial effects and survival outcomes associated with concordance between tissue and blood KRAS alterations in the pan‐cancer setting

“…Other studies demonstrated that, among various cancer types, concordance was variable with a range of ~70–98%, depending on the gene(s) examined . Several previous studies evaluated the concordance of KRAS alterations between tissue and ctDNA and found overall concordance to range 67–96% . These studies did not evaluate the impact of time interval between tissue biopsy and blood draw, nor did they examine the correlation with site of biopsy or the association with outcome for discordant vs .…”

Liquid biopsy - emergence of a new era in personalized cancer care

“…Adamo and colleagues did not detect any mutations in the cfDNA though tumors tissues had a KRAS G12D mutation [74]. Similarly, Grasselli and colleagues also saw very high heterogeneity and poor correlation in the mutational load between tissueplasma results [75]. These differences could potentially explained by low tumor burden [75] or ctDNA shedding or low total number of tumor cells in the primary tumor [76] or due to differences in protocol for isolating DNA from FFPE and plasma [44].…”

“…Similarly, Grasselli and colleagues also saw very high heterogeneity and poor correlation in the mutational load between tissueplasma results [75]. These differences could potentially explained by low tumor burden [75] or ctDNA shedding or low total number of tumor cells in the primary tumor [76] or due to differences in protocol for isolating DNA from FFPE and plasma [44]. Also, formalin fixation introduces DNA denaturation, and introduction of nonreproducible sequence alterations in DNA [77].…”

Liquid Biopsy for the Management of Patients with Colorectal Cancer

“…We previously reported the detection of KRAS mutations in cfDNA from 5 of 55 mCRC patients (9%) with wild-type KRAS in their primary tumors [23]. Other researchers reported that KRAS mutation in cfDNA is a negative biomarker of EGFR blockade chemotherapy [23][24][25][26][27].…”