Cancer is a genetic disease at cellular level. The genetic changes
leading to cancer is caused by multitude of factors. Viruses can also cause
cancer .Worldwide, cancer viruses are estimated to cause 15 to 20 percent of
all cancers in humans. The factors deciding susceptibility to cancer in the
setting of viral infection include the
host's genetic makeup, mutation occurrence, exposure to cancer causing agents,
and immune impairment. Viruses also
initiate cancer development by suppressing the host's immune system,
apart from altering host genes.
The cancer cells are characterized by the ability to grow uncontrollably. This can
result from having control of their own growth signals, losing sensitivity to
anti-growth signals, and losing the ability to undergo apoptosis
or programmed cell death. Cancer cells don't experience biological aging and
maintain their ability to undergo cell division
and growth.This causes tumour to grow continuously.
Transformation begins when a virus infects and genetic changes are
intiated in a cell. The infected cell becomes regulated by the viral genes and
gets the ability to undergo abnormal new growth. Many tumour causing viruses
have been identified.
There are two classes of cancer viruses: DNA and RNA viruses. Several
viruses have been linked to certain types of cancer in humans. These viruses
have varying ways of reproduction and represent several different virus
families.The viruses causing cancers can be DNA viruses or RNA viruses.
DNA Viruses
• The Epstein-Barr virus
has been linked to Burkitt's lymphoma. This virus infects B cells of the immune
system and epithelial
cells.
• The hepatitis B virus
has been linked to liver cancer in people with chronic infections.
• Human papilloma
viruses have been linked to cervical cancer and head and neck cancers. They
also cause warts and benign papillomas.
• Human herpes virus-8
has been linked to the development of Kaposi sarcoma. Kaposi sarcoma causes
patches of abnormal tissue to develop in various area of the body including
under the skin,
in the lining of the mouth, nose, and throat or in other organs.
RNA Viruses
• Human T lymphotrophic
virus type 1 (HTLV-I), a retrovirus, has been linked to T-cell leukemia.
• The hepatitis C virus
has been linked to liver cancer in people with chronic infections.
Source About.com
