Activating K-Ras mutations outwith 'hotspot' codons in sporadic colorectal tumours - implications for personalised cancer medicine.
BACKGROUND
Response to EGFR-targeted therapies in colorectal cancer patients has been convincingly associated with Kirsten-Ras (K-Ras) mutation status. Current mandatory mutation testing for patient selection is limited to the K-Ras 'hotspot' codons 12 and 13.


METHODS
Colorectal tumours (n=106) were screened for additional K-Ras mutations, phenotypes compared in transformation and Ras GTPase activating assays and gene and pathway changes induced by individual K-Ras mutants identified by microarray analysis. Taqman-based gene copy number and FISH analyses were used to investigate K-Ras gene amplification.


RESULTS
Four additional K-Ras mutations (Leu(19)Phe (1 out of 106 tumours), Lys(117)Asn (1 out of 106), Ala(146)Thr (7 out of 106) and Arg(164)Gln (1 out of 106)) were identified. Lys(117)Asn and Ala(146)Thr had phenotypes similar to the hotspot mutations, whereas Leu(19)Phe had an attenuated phenotype and the Arg(164)Gln mutation was phenotypically equivalent to wt K-Ras. We additionally identified a new K-Ras gene amplification event, present in approximately 2% of tumours.


CONCLUSIONS
The identification of mutations outwith previously described hotspot codons increases the K-Ras mutation burden in colorectal tumours by one-third. Future mutation screening to facilitate optimal patient selection for treatment with EGFR-targeted therapies should therefore be extended to codon 146, and in addition should consider the unique molecular signatures associated with individual K-Ras mutations.
Biomedical Research Institute, Ninewells Hospital and Medical School, Dundee, UK.
G
G
Smith
R
R
Bounds
H
H
Wolf
R J C
RJ
Steele
F A
FA
Carey
C R
CR
Wolf
D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D003062:Codon / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D011905:Genes, ras; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D008954:Models, Biological; D009154:Mutation / Q000235:genetics / Q000502:physiology; D041681:NIH 3T3 Cells; D018579:Patient Selection; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D057285:Precision Medicine / Q000379:methods / Q000639:trends; D014410:Tumor Stem Cell Assay
D003062:Codon