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.

NAT2 activity can be determined from a spontaneous urine probe in most subjects by quantification of caffeine metabolites arising from non-standardized dietary caffeine exposure using LC-MS/MS. This may facilitate the phenotyping procedure.

The major determinant of drug accumulation in three diverse cell line phenotypes was lactone chemical stability in culture medium.

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