Webster's New World Medical Dictionary

carboxyhemoglobin
Hemoglobin that has car-
bon monoxide instead of the normal oxygen bound
to it. Carbon monoxide has a much stronger bind-
ing to hemoglobin than oxygen. Carboxyhemoglobin
is formed in carbon monoxide poisoning and leads
to oxygen deficiency in the body. The source of the
carbon monoxide may be exhaust (such as from a
car, truck, boat, or generator), smoke from a fire,
or tobacco smoke. The level of carboxyhemoglobin
is a measure of the degree of carbon monoxide
exposure.
carbuncle
A skin abscess (boil) that extends into
subcutaneous layers of skin, usually caused by local
infection with the bacteria Staphylococcus aureus.
Treatment includes antibiotics (typically in the form
of topical creams) and, in severe cases, surgical
drainage. See also 
abscess.
carcinoembryonic antigen
A protein found in
many types of cells that is associated with a devel-
oping fetus and tumors and measurable by blood
testing. Abbreviated CEA. Conditions that increase
CEA include smoking, infection, inflammatory
bowel disease, pancreatitis, cirrhosis of the liver,
and some benign tumors (in the same organs that
have cancers with increased CEA). The normal level
is less than 2.5 ng/ml (nanograms per milliliter) in
an adult nonsmoker and less than 5.0 ng/ml in a
smoker. Benign disease rarely elevates the CEA over
10 ng/ml. The main use of CEA test is as a tumor
marker, especially with intestinal cancer. The most
common cancers that elevate CEA are in the colon
and rectum. Others include cancer of the pancreas,
stomach, breast, and lung, as well as certain types of
thyroid and ovarian cancer. Levels over 20 ng/ml
before therapy are associated with cancer that has
already metastasized (spread). CEA tests are useful
in monitoring the treatment of CEA-rich tumors.
carcinogen
A substance or an agent that causes
cancer. The International Agency for Research on
Cancer has classified many substances and
processes as probably or definitely causing cancer
in humans. The agency has divided these substances
and processes into three categories: agents (such as
arsenic, asbestos, and benzene); mixtures (such as
in coal tars, tobacco products, and smoke); and
exposures (such as in aluminum production, shoe
manufacturing and repair, and the rubber industry).
One of the best-known carcinogens is ultraviolet
radiation from sunlight causing skin cancers.