Viruses and Cancer

Viruses and Cancer

The Disease

Cancer is a family of diseases

characterized by uncontrolled

cell proliferation. The growth

of normal animal cells is carefully regulated to meet the

needs of the complete organism. In

contrast, cancer cells grow in an

unregulated  manner. ultimately

invading and interfering with the

function of normal tissues and

organs. Cancer is the second most

common cause of death  (next 10 heart

disease) in the United States. Approximately

one out of every three Americans

will develop cancer at some

point in life and, in spite of major

advances in treatment, nearly one out

of every four Americans ultimately

die of this disease. Understanding the

causes of cancer and developing more

effective methods of cancer treatment

therefore represent major goals of

medical  research.

Molecular and Cellular Basis

Cancer is now known to result from

mutations in the genes that normally

control cell proliferation. The major

insights leading to identification of

these genes came from studies of

viruses that cause cancer in animals,

the prototype of which was isolated

by Peyton Rous in 1911. Rous found

that sarcomas (cancers of connective

tissues) in chickens could be transmitted

by a virus, now known as Rous

sarcoma virus. or RSV. Because RSV is

a retrovirus with a genome of only

10,000 base pairs, it can be subjected

to molecular analysis much more

readily than the complex genomes of

chickens or other animal cells can.

Such studies eventually led to identified 

gene (oncogene) carried by the virus,

and to the discovery of related genes

in normal cells of all vertebrate

species, including humans. Some cancers

in humans are now known to be

caused by viruses; others result from

mutations in normal cell genes similar

to the oncogene first identified in RSV.

Prevention and Treatment
The human cancers that are caused by
viruses include cervical and other
anogenital cancers  (papilloma

viruses), liver cancer (hepatitis Band

C viruses), and some types of lymphomas

(Epstein-Barr virus and

human T-celll lymphotropic virus).

Together, these virus-induced cancers

account for about 20% of world wide:

cancer incidence. In principle. these

cancers could be prevented by vaccination

against the responsible viruses,

and considerable progress in this area

has been made by the development of

an effective vaccine against hepatitis B virus.

Other human cancers are caused by

mutations in normal cell genes, most

of which occur during the lifetime of

the individual rather than being inherited.

Studies of cancer-causing viruses

have led to the identification of many

of the genes responsible for non-virus induced

cancers, and to an understanding

of the molecular mechanisms

responsible for cancer development.

Major efforts are now under way to

use these insights into the molecular

and cellular biology of cancer to

develop new approaches to cancer

treatment. Indeed, the first designer

drug effective in treating a human cancer

(the drug s TI-571 or Gleevec, discussed

in chapter 18) was developed

against a gene very similar to the

oncogene of RSV.

Reference

ROllS, P. 1911. A sart:oma of the fowl transmissible

by an agent separable from the

tumor cells. ,. Exp. Merl. 13: 397-411.


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