Concordance Between Blood- And Tumor-Based Detection Of Ras Mutations To Guide Therapy In Metastatic Colorectal Cancer

217 Background: The study of RAS 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 mCRC patients. Methods: We conducted a study to evaluate RAS concordance in several hospitals in Galicia, Northwest of Spain. We analyzed samples from 380 patients with mCRC in Galicia. RAS genotyping in plasma was performed using OncoBEAM RAS CRC kit, Sysmex and compared with the PyroMark Q24 System, Qiagen for FFPE-tissue analysis. Clinical data were collected from electronical reports from each patient. We analyzed the clinical features that can be related with discordant cases. Results: The overall percent of agreement was 83%, with a positive concordance of 79% (143/180 patients) and a negative concordance of 87% (116/132 patients). Taking into account the clinical features of the patients, those with only liver metastasis showed a higher level of concordance (88,8%) and the highest level was in the group of patients that presented liver metastasis and another location (91,3%). On the other hand, patients with only peritoneal disease showed the lowest level of agreement (68,2%), and the absence of liver metastasis was a significant factor of discordance of RAS (71% vs 28%, p<0.0001). Conclusions: The high overall concordance between plasma and tissue RAS mutation support the liquid biopsy technology as an alternative to tissue testing for RAS characterization in mCRC patients, especially in patients with liver metastasis and less in those with peritoneal disease. These results reinforce the use of liquid biopsy as a non-invasive tool for guiding targeted therapy in our patients. [Table: see text]