RT Journal Article SR Electronic T1 Intratumorous heterogeneity for RAS mutations in a treatment-naïve colorectal tumour JF Journal of Clinical Pathology JO J Clin Pathol FD BMJ Publishing Group Ltd and Association of Clinical Pathologists SP 720 OP 723 DO 10.1136/jclinpath-2017-204327 VO 70 IS 8 A1 Sebastian Lunke A1 Belinda Lee A1 Sevastjan Kranz A1 Peter Gibbs A1 Paul Waring A1 Michael Christie YR 2017 UL http://jcp.bmj.com/content/70/8/720.abstract 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.