PT - JOURNAL ARTICLE AU - Lunke, Sebastian AU - Lee, Belinda AU - Kranz, Sevastjan AU - Gibbs, Peter AU - Waring, Paul AU - Christie, Michael TI - Intratumorous heterogeneity for RAS mutations in a treatment-naïve colorectal tumour AID - 10.1136/jclinpath-2017-204327 DP - 2017 Aug 01 TA - Journal of Clinical Pathology PG - 720--723 VI - 70 IP - 8 4099 - http://jcp.bmj.com/content/70/8/720.short 4100 - http://jcp.bmj.com/content/70/8/720.full SO - J Clin Pathol2017 Aug 01; 70 AB - Activating mutations in KRAS and NRAS genes in patients with colorectal cancer (CRC) are associated with a lack of response to treatment with anti-epidermal growth factor receptor (EGFR) therapies. Mutations in these genes are thought to be mutually exclusive, however reports have described CRCs with two activating rat sarcoma (RAS) mutations. This has fuelled discussion about whether these mutations are the result of intratumorous heterogeneity, or if they are co-occurring in the same cancer cell clone. We present a case of a colorectal tumour with three RAS mutations detected during routine diagnostic testing. Further detailed analysis with laser capture microdissection and next generation sequencing excluded the possibility of all three mutations being present in the same clone, presenting the highest resolution evidence of intratumorous heterogeneity of RAS mutations to date.