Abstract 437P
Background
The study of RAS status using circulating tumor DNA (ctDNA) provides a good alternative for the detection and monitoring of RAS mutations during therapy course. Liquid biopsy has the advantage of being less invasive than conventional tissue biopsy. Therefore, it is necessary to determine the degree of concordance of RAS status between plasma and tissue samples from metastatic Colorectal Cancer (mCRC) patients. We already know that sidedness (right or left) is related with different molecular biology, conditioned predictive and prognostic factors along the course of the disease.
Methods
We conducted a study to evaluate the concordance of RAS status between plasma and tissue samples of 301 patients from several hospitals in Galicia, Northwest of Spain. RAS genotyping in plasma was performed using OncoBEAM RAS CRC kit (Sysmex) and compared to the standard of care technology for FFPE-tissue analysis. Clinical data were collected from electronical reports from each patient. We analyzed the clinical profiles of the mCRC patients to investigate the causes of discordance, such as origin side of the primary tumour and the site of metastasis.
Results
Tumours from left-side were more concordant in the RAS status between tissue and blood analysis (91.3%), following by rectum (83.5%) and right-side (76.9%) (table). The mCRC subpopulation diagnosed of right-side primary tumours presented more frequently spread to peritoneal lesions and patients with rectum primary presented higher frequency of lung metastatis. Both peritoneal and lung metastasis had less concordance than liver. Table: 437P
Concordance between analysis of the RAS locus in solid tissue and blood liquid biopsy
| Primary Origin | Concordance% | Sensitivity% | Specificity% |
| Left-sided | 91.3 | 87.1 | 95.3 |
| Right-sided | 76.9 | 73.3 | 85 |
| Rectum | 83.5 | 82.5 | 85 |
Conclusions
Variations in the anatomical location of metastases (lung and peritoneal disease) and primary sidedness (right-side and rectum) were associated with the lack of concordance, conditioned by the absence of liver metastasis in discordant cases.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
IDICHUS.
Disclosure
E. Brozos-Vázquez: Travel/Accommodation/Expenses: Amgen, Merck, Pierre Fabre, Novartis, Roche. R. Lopez Lopez: Advisory/Consultancy: Roche, AstraZeneca, Merck, MSD, BMS, Bayer, Novartis, Janssen, Lilly, Pfizer, LEO; Travel/Accommodation/Expenses: PharmaMar, Roche, BMS, Pierre Fabre; Research grant/Funding (institution): Roche, Merck. All other authors have declared no conflicts of interest.