The phosphatidylinositol 3-kinase (PI3K)-AKT signalling pathway is involved in the regulation of diverse cellular processes, including cell growth, survival and motility. Abnormal activation of this pathway is frequently observed in various cancer types, leading to aberrant cell cycle progression, altered adhesion and motility, inhibition of apoptosis and induction of angiogenesis [
1]. It has been previously reported that genetic alterations involving various members along this signalling pathway could lead to its activation in cancer. These include mutation, allelic loss or promoter methylation of the negative regulator
PTEN [
2]; or alternatively, chromosomal amplification or over-expression of the positive regulators
PIK3CA [
3‐
5] and the various
AKT kinases [
6,
7]. Furthermore, changes in other related pathways that are commonly altered in cancer, such as those involved in growth factor stimulation via the G-protein-coupled receptors or through direct interaction with the activated form of small GTPase RAS, can also lead to PI3K-AKT pathway activation [
8]. Activation of this pathway results in the phosphorylation of AKT at Thr-308/309 and Ser-473/474. These phosphorylated forms of AKT proteins have been detected by Western blot or immunohistochemistry in various cancer types, suggesting the frequent activation of PI3K-AKT pathway in the carcinogenic process [
7,
9].
Although genetic changes along the PI3K-AKT pathway have been repeatedly documented in brain, ovarian, endometrial, breast, prostate and thyroid cancers [
1,
2], reports on its mechanism of activation in gastric cancer are limited. Gastric cancer is the second most common cancer worldwide but its molecular basis of tumourigenesis is still poorly understood. Previous immunohistochemical study has demonstrated the presence of the phosphorylated form of AKT in 78% of gastric cancer [
10], suggesting that activation of this pathway may also be common in gastric cancer. Though loss of heterozygosity (LOH) involving the
PTEN locus has been demonstrated in 47% of gastric cancer in a recent study, mutation or promoter methylation was absent even in cases with LOH [
11]. Thus data from this study could not support the two-hit inactivation of
PTEN in gastric cancer, while the biological significance of
PTEN haploinsufficiency remains controversial. Alternatively, amplification of
AKT1 has been reported in a single case of gastric cancer [
12], and amplification of
PIK3CA associated with elevated mRNA levels has been found in 36% of gastric cancer [
11]. More recently, Samuels
et al. screened a diverse spectrum of human cancers for mutation in 16
PI3K or
PI3K-like genes and found a high frequency of somatic mutation in
PIK3CA, which encodes the p110α catalytic subunit. Major screening in colorectal cancer (CRC) identified
PIK3CA mutations in 74 out of 234 (32%) cases, while mutations were also noted in 3 out of 12 (25%) gastric cancers. Reported mutations were mostly of missense type, and clustered within 2 regions in the helical and kinase domains. Expression of a "hot-spot" mutant, H1047R, conferred a significant up-regulation of lipid kinase activity of PIK3CA, suggesting it as an activating mutation [
13]. In this study, we have examined a series of 94 human gastric adenocarcinomas for
PIK3CA mutation. We have also examined
PIK3CA expression level by extracting data from a large-scale gene expression profiling study previously performed for these cases [
14,
15]. Using SAM, genes with significant correlating expression with
PIK3CA have also been identified.