Cancer Causing Agents - Carcinogens (cont.)
Because of the importance of cancer and agents which may cause it,
we here provide some of the highlights of this Report.
Listing in the Report
A listing in the Report does not by itself establish
that a substance presents a cancer
risk to an individual in daily life.
The Report also does not try to balance the potential benefits of exposures
to certain carcinogenic
substances in special situations. For example, a number of drugs used to treat
cancer have been shown to increase the occurrence of secondary cancers. In these
instances, the benefits of exposure to the drugs for treatment or prevention of
a specific disease have been determined by the Food & Drug Administration
(FDA) to outweigh the additional cancer risks associated with their use. People
should not make decisions concerning the use of a given drug, or any other
listed agent, based solely on the information contained in the Report. Decisions
of this type should be made only after consulting with a physician or other appropriate specialist about both risks and benefits.
"Known" versus "Reasonably
Anticipated" To Be a Carcinogen
An agent or exposure can be listed in the Report as
"known to be a human carcinogen" or as "reasonably anticipated to be a human carcinogen."
The "known" category is reserved for those substances for which there is sufficient
evidence of carcinogenicity from studies in humans that indicates a cause and effect relationship
between the exposure and human cancer.
The "reasonably anticipated" category includes
those substances for which there is limited evidence of carcinogenicity in humans
and/or sufficient evidence of carcinogenicity in experimental animals.
Six substances have been added to the "known" category:
- Hepatitis B virus (HBV) and
hepatitis C virus (HCV) are viruses that cause acute or chronic liver
disease. They are listed in the report as "known human carcinogens" because
studies in humans show that chronic hepatitis B and hepatitis C infections
cause liver cancer. Approximately one million United States residents are
chronically infected with HBV, which primarily is transmitted through sexual
contact (50%) and intravenous drug use (15%).
HCV is the leading cause of liver disease in the
United States with more than three million people infected. The major risk
factor for hepatitis C infection is illegal intravenous drug use, which
accounts for 60 percent of acute infections in adults. The incidence of both
hepatitis B and hepatitis C infections is decreasing among United States
residents. A vaccine is available for preventing hepatitis B infection but not
hepatitis C infection. Infections can also be prevented by screening blood
supplies, and by reducing contact with contaminated
fluids in health care settings.
- Human papillomaviruses (HPVs) are viruses that are sexually transmitted and can infect genital
and mucous membranes. Some of these genital mucosal type HPVs are listed in
the report as "known human carcinogens" because studies show they cause
cervical cancer in women.
Approximately 20 million people in the United States are infected with
genital HPVs, and 5.5 million new infections occur each year. Most
people infected do not have symptoms, but some develop genital warts or
- X-radiation and gamma-radiation are listed in the report as
"known human carcinogens" because human studies show that exposure to
these kinds of radiation causes many types of cancer including leukemia
and cancers of the thyroid, breast and lung. The risk of
developing cancers due to these forms of ionizing radiation depends to some
extent on age at the time of exposure. Childhood exposure is linked to an
increased risk for leukemia and thyroid cancer. Exposure during reproductive years increases the risk for breast
cancer, and exposure
later in life increases risk for lung cancer. Exposure to X-radiation
and gamma radiation has also been shown to cause cancer of the salivary
glands, stomach, colon, bladder, ovaries, central nervous system and