** I received this background from the BC Cancer Agency in Canada. I thought I'd share it because it explains a lot of useful information on HDGC.
Worldwide, gastric (stomach) cancer is the second most
common form of cancer. Although the total number of individuals diagnosed with
gastric cancer have been decreasing over the years in North America and Western
Europe, it is still relatively common in certain parts of Asia and Latin
America.
The stomach is part of the digestive system and is located
in the upper abdomen under the ribs. Gastric cancer can develop in any part of
the stomach and may spread throughout the stomach and to other organs. Gastric cancer
is treatable if it’s diagnosed in the early stages of the disease. The 5-year
survival rate for gastric cancer is 90 percent when the cancer is detected in
its earliest Stages. When the cancer has spread, the outlook is not as good for
the patient. Unfortunately, most people do not receive a diagnosis until the
cancer is more advanced. The reason for the lack of early diagnosis is that the
cancer is difficult to detect in its early stages. Generally, there are no symptoms and the only evidence may
be microscopic bleeding from the surface of the stomach. By the time symptoms
do occur, the disease is often at a more advanced stage and no longer treatable.
The diagnosis is sometimes made more difficult because the symptoms are very
similar to those caused by ulcers.
The exact causes of gastric cancer are still largely
unknown. Most cases of gastric cancer are sporadic in nature (that is, not
inherited). Some of the risk factors in the sporadic cases include increasing
age (generally people over 60 years), dietary factors, Helicobacter pylori
infection, smoking, alcohol consumption, and a disorder of the blood called
pernicious anemia. In about 1-3 % of all individuals who are diagnosed with gastric
cancer and who have a strong family history of gastric cancer, the condition is
caused by inherited mutations (changes) in genes that predispose individuals to
gastric cancer.
There are 2 main types of gastric cancer - diffuse type and
intestinal type. The intestinal type is more common than the diffuse type. The
patients are usually older, patients are more likely to be male and it forms a
typical visible tumor in the stomach. H pylorĂ plays an important factor in its
development.
Diffuse type gastric cancer is somewhat more common in
younger patients and it occurs in similar numbers in men as in women. It is not
known what role Helicobacter pylori plays in the development of this type of cancer.
Diffuse gastric cancer often presents with diffuse thickening of the stomach
wall, rather than a visible mass (linitis plastica).
Inherited information is contained in structures called
chromosomes that are found in every cell of our body. We have 46 chromosomes
that occur in pairs; 23 from our mother and 23 from our father. Each chromosome
is made up of hundreds to thousands of genes. Hence, the genes also come in
pairs. Genes are packages of inherited information and act as instructions for
making proteins (specific substances in our bodies) that help it to function
properly. An alteration in this genetic information can cause a change in the
instructions of the gene and interfere with normal protein function and hence
proper body functions. These gene alterations are called mutations. There are
certain genes that cause an increased chance to develop cancer when they have mutations.
These genes are known as cancer susceptibility genes.
Most cancers occur as a result of sporadic mutations that
occur in the body during a person’s life-time.
These mutations tend to occur as mistakes when the cells undergo
division (a normal process) or in response to environmental factors. These
mutations are not passed on to children. Hereditary Cancer occurs when a gene mutation
is passed down from parent (through the egg or the sperm) to child. Since the
mutation is present right from the beginning, it is found in every cell of the
body. Cancer will develop only when both genes in a pair are mutated,
Hereditary cancer tends to develop at a younger age since the individual is
already born with one mutation and needs only to acquire one additional
sporadic mutation in the other gene for cancer to occur.
There are believed to be several genes involved in
hereditary gastric cancer. One of these, E-cadherin (or CDH1) is mutated in
only one-third (33%) of the families that have hereditary diffuse gastric
cancer. That means that other families with either the diffuse or intestinal
type gastric cancer have mutations in other cancer genetic susceptibility
genes.
E-cadherin is located on chromosome 16. Everybody has two
chromosome 16’s and therefore two E-cadherin genes. E-cadherin is an important
protein that helps to hold cells together. In cancer cells, when E-cadherin is either
partly or completely missing, the cells detach themselves from each other and from
the whole mass that holds everything together. If an individual inherits one
E-cadherin gene with a mutation, damage to the remaining normal E-cadherin gene
may be the event that starts off the stomach cancer. In individuals who inherit
a mutated E-cadherin gene, the chance of developing stomach cancer depends on whether
the person is male or female. In males, the chance of stomach cancer is 67%
over the lifetime. In females, the lifetime chance of getting stomach cancer is
83%. Females with the mutation are also believed to have a 39% lifetime chance
of having lobular (the part of the breast where milk is made) breast cancer.
Therefore, not everyone who carries the mutation develops cancer but the risk
is increased considerably over the general population risk (2000 times higher
than the general population). When one parent carries a mutation in a cancer
susceptibility gene such as E-cadherin, each one of his or her children has a
50% chance of inheriting that mutation. Males and females are both capable of
passing the mutation down as well as inheriting the mutation.