cumulative risk for advanced gastric cancer. In this rare disorder,
CDH1 mutation testing in families with a history of gastric cancer
and prophylactic gastrectomy in mutation-positive patients are
recommended for management.(70)
HOST GENETIC POLYMORPHISMS AND
GASTRIC CANCER RISK
Host genetic polymorphisms may have an impact on host responses
to gastric inflammation and acid secretion, thereby interacting
with H. pylori infection in gastric carcinogenesis. A series of
single nucleotide polymorphisms (SNPs) of susceptibility genes
have been implicated. El-Omar et al(71)
were the first to report that
interleukin-1 (i.e. IL1B) gene cluster polymorphisms, suspected of
enhancing production of IL1B, are associated with an increased
risk of both hypochlorhydria-induced H. pylori and gastric cancer.
IL1B is an important pro-inflammatory cytokine and a powerful
inhibitor of gastric acid secretion. Host genetic factors that affect
IL1B may determine why some individuals infected with H. pylori
develop gastric cancer, while others do not.(71)
The inflammatory
response-related genes that have been most frequently studied
are interleukin genes IL1B, IL1RN, IL8 and IL10, and tumour
necrosis factor-alpha (TNFA), coding for the proteins IL-1b,
IL-1ra, IL-8, IL-10, and TNF-a, respectively. However, the results
of these studies are not consistent across Asian and non-Asian
populations. A recent meta-analysis(72)
examined the relationship
between these genetic polymorphisms and gastric cancer risk.
Overall, the study showed statistically significant associations in
IL1RN2 and IL10-592A carriers. In studies from Asian populations,
an increased risk of gastric cancer among IL10-1082G carriers
and a decreased risk among IL1B-31C carriers were observed.
Studies from non-Asian populations showed an increased risk
among IL1RN2 carriers and a decreased risk among IL10-1082G
carriers. Furthermore, studies from non-Asian populations also
observed increased risks among carriers of IL1B-511T, IL1B-31C
and IL1RN2 for cardia gastric cancer, but this was not statistically
significant in Asian populations. In Asian populations, IL1B-31C
carriers were found to have a decreased risk and IL1RN2 carriers
an increased risk for non-cardia gastric cancer. An increased risk
was shown in carriers of the IL1B-511T, IL1RN2 and TNFA-308A
alleles among non-Asian populations. In studies reporting results
for intestinal type gastric cancer, Asian populations showed a
statistically significant decreased risk among IL1B-511T and IL1B-
31C carriers, and an increased risk among non-Asian IL1RN2
carriers. For studies from non-Asian populations, increased risks
for IL1RN2 and TNFA-308A carriers and a decreased risk of
diffuse type cancer among IL10-1082G carriers were found.(72)
MOLECULAR SUBTYPES OF GASTRIC
CANCER
The Lauren classification of gastric cancer is widely used, as it
distinguishes two main subtypes that are biologically different,
with distinct clinical and epidemiological profiles.(21)
However,
in clinical practice, this classification is not useful for predicting
treatment response or survival. A robust molecular classification
system, based on genomic/molecular analysis, could potentially
provide insights into oncogenic mechanisms and identify unique
molecular drivers that could be correlated with survival and
treatment response. Building upon prior efforts in microarraygene expression profiling to discover molecular subtypes of
gastric cancer that were limited by small sample sizes, Lei et al(73)
compared gene expression patterns in 248 Singapore cases of
gastric cancer using hierarchical clustering with iterative feature
selection. The study identified three molecular signatures,
which were further validated in 70 cases of gastric cancer from
Australia. The first subtype had high activity of the epithelialmesenchymal transition pathway, and was hence termed
mesenchymal. The second subtype was termed proliferative
because it was characterised by gene sets associated with the
cell cycle; it was also associated with high activities for several
oncogenic pathways such as E2F, MYC and RAS. The third
subtype was termed metabolic, as it was characterised by gene
sets from several KEGG metabolism pathways. Interestingly,
the mesenchymal and proliferative subtypes largely coincided
with Lauren’s diffuse and intestinal subtypes (70% and 75%,
respectively), whereas the metabolic subtype was nearly evenly
split between diffuse and intestinal subtypes. However, the
metabolic subtype had features of spasmolytic polypeptideexpressing metaplasia. In terms of therapeutic implications, the
key finding of Lei et al’s study was that the metabolic subtype
had in vitro sensitivity to 5-fluorouracil, which also appeared to
be true in vivo, based on correlation with actual clinical data
in Singapore. The mesenchymal subtype was found to be more
sensitive to drugs that target the phosphatidyl