NRAS and colorectal carcinoma: In terms of the variants of relevance to CRC, over two-thirds of laboratories reported the two mutations in NRAS, and between 36.8% and 69% correctly identified the clinically relevant variants in KRAS. The variant allele frequency of the NRAS variants was 7.4%, compared with 4.3% for the KRAS variants, which may have explained the lower level of detection for the latter gene variants.