Ionizing
radiation
Sources of ionizing radiation, such as radon gas, can cause
cancer. Prolonged exposure to ultraviolet radiation from the sun
can lead to melanoma and other skin malignancies.
Infectious diseases
Furthermore, many cancers originate from a viral infection;
this is especially true in animals such as birds, but also in
humans, as viruses are responsible for 15% of human cancers
worldwide. The main viruses associated with human cancers are
human papillomavirus, hepatitis B and hepatitis C virus,
Epstein-Barr virus, and human T-lymphotropic virus. Experimental
and epidemiological data imply a causative role for viruses and
they appear to be the second most important risk factor for
cancer development in humans, exceeded only by tobacco usage.
The mode of virally-induced tumors can be divided into two,
acutely-transforming or slowly-transforming. In acutely
transforming viruses, the viral particles carry a gene that
encodes for an overactive oncogene called viral-oncogene (v-onc),
and the infected cell is transformed as soon as v-onc is
expressed. In contrast, in slowly-transforming viruses, the
virus genome is inserted, especially as viral genome insertion
is an obligatory part of retroviruses, near a proto-oncogene in
the host genome. The viral promoter or other transcription
regulation elements in turn cause overexpression of that
proto-oncogene, which in turn induces uncontrolled cellular
proliferation. Because viral genome insertion is not specific to
proto-oncogenes and the chance of insertion near that
proto-oncogene is low, slowly-transforming viruses have very
long tumor latency compared to acutely-transforming viruses,
which already carry the viral oncogene.
Hepatitis viruses, including hepatitis B and hepatitis C, can
induce a chronic viral infection that leads to liver cancer in
0.47% of hepatitis B patients per year (especially in Asia, less
so in North America), and in 1.4% of hepatitis C carriers per
year. Liver cirrhosis, whether from chronic viral hepatitis
infection or alcoholism, is associated with the development of
liver cancer, and the combination of cirrhosis and viral
hepatitis presents the highest risk of liver cancer development.
Worldwide, liver cancer is one of the most common, and most
deadly, cancers due to a huge burden of viral hepatitis
transmission and disease.
Advances in cancer research have made a vaccine designed to
prevent cancer available. In 2006, the US FDA approved a human
papilloma virus vaccine, called Gardasil®. The vaccine protects
against four HPV types, which together cause 70% of cervical
cancers and 90% of genital warts. In March 2007, the US CDC
Advisory Committee on Immunization Practices (ACIP) officially
recommended that females aged 11-12 receive the vaccine, and
indicated that females as young as age 9 and as old as age 26
are also candidates for immunization.
In addition to viruses, researchers have noted a connection
between bacteria and certain cancers. The most prominent example
is the link between chronic infection of the wall of the stomach
with Helicobacter pylori and gastric cancer.
Causes Hormonal
imbalances & Immune system dysfunction >>
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Cancer
Classification
1. Nomenclature
2. Adult cancers
3. Childhood cancers
Signs and symptoms
Diagnosis
1. Investigation
2. Biopsy
Treatment
1. Surgery
2. Radiation therapy
3. Chemotherapy
4. Targeted therapies
5. Immunotherapy
6. Hormonal therapy
7. Symptom control
8. Complementary and alternative
9. Treatment trials
Prognosis
1. Emotional impact
Causes
1. Chemical carcinogens
2. Ionizing radiation & Infectious diseases
3. Hormonal imbalances & Immune system dysfunction
4. Heredity & Other causes
Pathophysiology
1. Epigenetics
2. Oncogenes
3. Tumor suppressor genes
4. Cancer cell biology
4.1 Clonal evolution
4.2 Biological properties of cancer cells
Prevention
1. Modifiable ("lifestyle") risk factors
2. Diet
3. Vitamins
4. Chemoprevention
5. Genetic testing
6. Vaccination
7. Screening
Epidemiology
History
Research |
