A. Genetic Factor
The relationship between genetic and susceptibility to cancer has
been an important area of study for decades. For example, FAP (Familial
Adenomatous Polyposis) is an inherited colon cancer predisposition
condition in which thousands of polyps throughout the colon was
formed. FAP is caused by APC gene mutation with chromosomal locus
at 5q21-q22. If both of the parents are carriers, the chance to
develop FAP for their children is 75-80%. If only one of the parents
has the gene, then the probability of inheriting FAP is 50%. Therefore,
early detection and treatment is extremely important to reduce the
incidence of colon cancer.
The presence of BRCA1 or BRCA2 genes in breast cancer and ovarian
cancer is another example. Both a clear and detail family history
and an early detection of BRCA1 and BRCA2 are crucial criteria for
early diagnosis of breast cancer.
B. Environment Factors
1. Physical Factor
Physical factor: Physical carcinogenic factors include UV
light, some radioactive materials and burn injury.
Chronic mechanic stimulation:
Both frequent chronic cervical infections in female and frequent
urinary tract infection in male due to prolonged and non-retractable
foreskin (prepuce) are risk factors to cancers due to chronic stimulation
to genital tissue.
Radiation: It has been proved
that exposure to one high dose of radiation or being exposed to
long term small dose of radiation may cause cancers like leukemia,
hepatoma, lung cancer, breast cancer and other soft tissue cancers.
2. Chemical Carcinogen Factor
Over one thousand types carcinogens have been identified both from
natural and synthetic origin. Below are some common chemical carcinogens
in daily life:
- Polycyclic aromatic hydrocarbons such as tar, coarse paraffin,
and others. All these materials contain 3, 4- benzpyrene, a kind
of carcinogen that also exists in cigarettes.
- Dyes: such as aniline, benzedrine etc. are all strong carcinogens.
- Nitrite, aromatic amines and polycyclic aromatic hydrocarbons.
These are common in automobile waste, tobacco and smoked foods
and are carcinogens especially potent to the human digestive system.
Other inorganic materials including arsenic, chromium, nickel
and their associated compounds, and asbestos are all proven carcinogens.
3. Biological Carcinogens
In this group of carcinogen factors includes: virus, bacteria and
parasite.
Virus: Viruses have been associated with cancer
in humans. For example, Epstain-Barr Virus is closely related to
Nasopharyngeal Carcinoma (NPC), Herpes Simplex type II is related
to cervical cancer. HTLY-I and HTLY-II are related with leukemia.
Bacteria: the bacterium Helicobacter Pyloric has
been associated with the development of stomach cancer.
For the group of bacteria, the relation between HPV and cervical
cancer is a typical example.
Fungi: Aflatoxin is a naturally-occurring toxin
produced by molds and can be a contaminant in peanuts, corn, rice
and beans. It is one of the most extremely strong carcinogens from
food sources. Aflatoxin can induce liver cancer (hepatoma), renal
cancer, gastric cancer and soft tissue cancers.
Parasites: For parasites, Clonorchis is related
with primary hepatobiliary cancers. Some research reported that
the existing and proliferation of parasite in human may worsen and
deteriorate the condition of cancer though further detail study
is needed.
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