RAS mutation analysis in circulating tumor DNA from patients with metastatic colorectal cancer: the AGEO RASANC prospective multicenter study.

Background: RAS mutations are currently sought for in tumor samples, which takes a median of almost 3 weeks in western European countries. This creates problems in clinical situations that require urgent treatment and for inclusion in therapeutic trials that need RAS status for randomization. Analysis of circulating tumor DNA might help to shorten the time required to determine RAS mutational status before anti-epidermal growth factor receptor antibody therapy for metastatic colorectal cancer. Here we compared plasma with tissue RAS analysis in a large prospective multicenter cohort. Patients and methods: Plasma samples were collected prospectively from chemotherapy-naive patients and analyzed centrally by next-generation sequencing (NGS) with the colon lung cancer V2 Ampliseq panel and by methylation digital PCR (WIF1 and NPY genes). Tumoral RAS status was determined locally, in parallel, according to routine practice. For a minimal κ coefficient of 0.7, reflecting acceptable concordance (precision ± 0.07), with an estimated 5% of non-exploitable data, 425 subjects were necessary. Results: From July 2015 to December 2016, 425 patients were enrolled. For the 412 patients with available paired plasma and tumor samples, the κ coefficient was 0.71 [95% confidence interval (CI), 0.64-0.77] and accuracy was 85.2% (95% CI, 81.4% to 88.5%). In the 329 patients with detectable ctDNA (at least one mutation or one methylated biomarker), the κ coefficient was 0.89 (95% CI, 0.84-0.94) and accuracy was 94.8% (95% CI, 91.9% to 97.0%). The absence of liver metastases was the main clinical factor associated with inconclusive circulating tumor DNA results [odds ratio = 0.11 (95% CI, 0.06-0.21)]. In patients with liver metastases, accuracy was 93.5% with NGS alone and 97% with NGS plus the methylated biomarkers. Conclusion: This prospective trial demonstrates excellent concordance between RAS status in plasma and tumor tissue from patients with colorectal cancer and liver metastases, thus validating plasma testing for routine RAS mutation analysis in these patients. Clinical Trial registration: Clinicaltrials.gov, NCT02502656.

Morphological and biomechanical aspects of vulnerable coronary plaque.

Vulnerable plaque morphology has been described by gross pathology and intravascular ultrasound, but morphological criteria cannot fully explain vulnerability, which involves four distinct factors: 1) inflammatory and biological processes; 2) geometry; 3) composition; and 4) hemodynamic stress. These last three aspects underlie the biomechanical study of vulnerable plaque. By virtue of the nature of their evolution, atherosclerotic plaques tend to be excentric, and this is a crucial morphological feature, causing circumferential stress to peak in very specific juxta-luminal locations, where it can exceed the rupture threshold of collagen, the basic constituent of arterial architecture. The lipido-necrotic core covered by a fibrous cap, formed in young plaques, is another morphological feature, which, can also increase and concentrate circumference stress in the juxta-luminal fibrous cap. The larger the lipid core, the thinner the fibrous cap and the greater is the stress. There are also inflammatory processes in such areas, which tend to reduce cap thickness. Ruptures occur when this thickness falls below 65 microns. Heart rate, blood pressure and pulse pressure are all biomechanical factors affecting vulnerable arterial walls, increasing circumferential stress and material fatigue. Vulnerable plaques are almost always associated with positive arterial remodeling. Numerical simulation has shown such so-called compensatory remodeling to be exclusively due to the healthy arc stretching in vulnerable plaques. Positive remodeling is optimal when the healthy arc is around 170 degrees, which keeps the lumen area relatively stable as long as the plaque does not exceed 40% to 50%. This mechanism does not apply to concentric plaques. In conclusion, the mechanism of vulnerable plaque rupture is highly complex and multifactorial. This complexity more or less precludes prediction in individual cases: we are in the realms of chaos theory and acute sensitivity to initial conditions. The greatest caution is therefore required in any attempt to predict rupture from diagnostic imagery, which provides only morphological data on plaque's nature.