Encyclopedia of Health and Medicine

374 Cancer
marker. The cancers associated with elevated
blood CEA levels are carcinomas of the COLON and
RECTUM (COLORECTAL CANCER), PANCREAS, STOMACH,
BREAST, and lung. The developing fetus also produces
CEA, as do benign (noncancerous) tumors
of the gastrointestinal tract. In these circumstances
the presence of CEA in the blood circulation is
normal and not an indication of cancer. Cigarette
SMOKING AND CANCER treatment with CHEMOTHERAPY
or RADIATION THERAPY also can produce elevated
blood levels of CEA.
See also BREAST CANCER; CA-125; CARCINOMA; LUNG
CANCER; PANCREATIC CANCER; STOMACH CANCER; TUMOR
MARKERS.
carcinogen A substance that can cause cancer.
The most common carcinogen is cigarette smoke,
which is implicated in nearly all types of cancer
and most specifically LUNG CANCER, BREAST CANCER,
PROSTATE CANCER, pharyngeal cancer, STOMACH CAN-
CER, and COLORECTAL CANCER. Other significant carcinogens
include
• radon, a naturally occurring gas that results
from the deterioration of naturally occurring
uranium ubiquitously present in rocks and soil
• radiation, such as from overexposure to sunlight
(ultraviolet) or ionizing radiation such as
X-RAY and gamma-ray
• industrial chemicals such as benzene, vinyl
chloride, and arsenic
• pharmaceutical agents such as hormones (oral
contraceptives, estrogen supplements)
Some substances are beneficial in small
amounts and carcinogenic in large amounts or in
cumulative exposure over time, such as sunlight.
Certain medications, notably IMMUNOSUPPRESSIVE
MEDICATIONS and estrogen-containing drugs, may
cause cancer. Others are hazardous at nearly any
exposure level. CHEMOTHERAPY drugs, which effectively
treat and cure many types of cancer, are
themselves carcinogenic for certain types of
LEUKEMIA and LYMPHOMA. RADIATION THERAPY as well
increases the risk for subsequent cancers, depending
on the site of irradiation. Pathogens such as
viruses and BACTERIA cause certain kinds of cancer.
Limiting exposure to carcinogens reduces the
likelihood that they will have adverse health
effects. In the United States, federal and state regulations
provide guidelines for occupational exposure
to carcinogens. Other public health measures
attempt to reduce carcinogen exposure through
educational efforts.
COMMON CARCINOGENS
aflatoxins
arsenic
asbestos
benzene
beryllium
cadmium
chromium
cigarette smoke
cyclosporine
diethylstilbestrol (DES)
EPSTEIN-BARR VIRUS
ESTROGENS
ethylene oxide
formaldehyde
HELICOBACTER PYLORI
HEPATITIS B VIRUS
HUMAN PAPILLOMAVIRUS (HPV)
iodine-131
ionizing radiation
methyl chloride
radon
sunlight
tobacco
vinyl chloride
See also ASBESTOSIS; BERYLLIOSIS; CANCER PREVEN-
TION; CANCER RISK FACTORS; ENVIRONMENTAL CIGARETTE
SMOKE; ENVIRONMENTAL HAZARD EXPOSURE; LIFESTYLE
AND CANCER; OCCUPATIONAL HEALTH AND SAFETY;
PATHOGEN; RADON EXPOSURE; SMOKING AND CANCER.
carcinoma A cancerous tumor that arises from
epithelial cells. Epithelial cells form the surface
layer of tissue throughout the body: the SKIN,
mucous membranes, and serous membranes (lining
of the internal body cavities). Carcinoma is the
most common form of cancer. A carcinoma generally
carries the name of the tissue or site of its origin;
for example, basal cell carcinoma originates in
the basal cells of the skin and ADENOCARCINOMA
originates in a glandular structure. Treatment
depends on the nature, location, and size of the
carcinoma and may incorporate surgery, CHEMO-
THERAPY, RADIATION THERAPY, and IMMUNOTHERAPY.
Tumor
ADENOCARCINOMA
basal cell carcinoma
intraductal carcinoma
large-cell carcinoma
lobular carcinoma
small-cell carcinoma
squamous cell carcinoma
TYPES OF CARCINOMA
Location
glandular tissue
SKIN
BREAST
lung
BREAST
lung
skin, mucous membranes