In metastatic colorectal cancer, KRAS and NRAS genotyping is mandatory before prescription of panitumumab or cetuximab. In order to perform such molecular tests, the French National Cancer Institute has set up a nationwide network of molecular centers. We report here the percentage of these mutations according to a prospective nonselected cohort of incident metastatic colorectal carcinoma patients. A total of 6,803 patients were tested between July 1, 2013, and December 31, 2013. Overall, 49.06% of patients harbored a mutation in either KRAS or NRAS. Mutations of NRAS exons 3 and 4 were very rare. No NRAS exon 3 at c.59 or exon 4 at c.117 mutations were retrieved, and only 1 NRAS exon 4 at c.146 mutation was detected. This present cohort is likely to represent most of the incident cases of metastatic colorectal adenocarcinomas arising in France over 6 months and is to our knowledge the largest population set genotyped for these genes in this condition. This is a unique opportunity to observe the frequency of RAS mutations regardless of most inclusion bias.
©2015 American Association for Cancer Research.