Tyrosine kinases (TKs) are central regulators of signaling pathways that control differentiation, transcription, cell cycle progression, apoptosis, motility, and invasion (1). Although a few TK genes have been shown to be mutationally altered in specific human cancers (1), it is not known how many or how often members of the TK gene family are altered in any particular cancer type. In this study, we have used high-throughput sequencing technologies and bioinformatics from the human genome project to address this question. A recent analysis organized the protein kinase complement of the human genome (the “kinome”) into a dendrogram containing nine broad groups of genes (2). We selected one major branch of this dendrogram, containing three of the nine major groups, for mutational analysis. These included the 90 tyrosine kinase genes (TK group), the 43 tyrosine kinase–like genes (TKL group), and the 5 receptor guanylate cyclase genes (RGC group). To evaluate whether these genes were genetically altered in colorectal cancer, we initially analyzed all exons encoding their predicted kinase domains. A total of 819 exons from all annotated TK, TKL, and RGC genes containing this domain were extracted from genomic databases (3). These exons were polymerase chain reaction (PCR)-amplified from DNA derived from 35 colorectal cancer cell lines and were directly sequenced (3).

From the 4 megabases (Mb) of sequence information obtained, we identified 14 genes that contained somatic (ie, tumor-specific) mutations within their kinase domains. These genes were then analyzed for mutations in another 147 colorectal cancers (3). We identified 46 mutations in the 14 genes, 2 of which were synonymous; the rest were either nonsynonymous or splice site alterations (Table 1; table S1). All of these mutations were shown to be somatic in the cancers that could be assessed by sequencing of DNA from matched normal tissue. Two independent observations support the hypothesis that the mutations found in the seven genes mutated in more than one tumor in our