marker. The cancers associated with elevated
blood CEA levels are carcinomas of the COLONand
RECTUM(COLORECTAL CANCER), PANCREAS, STOMACH,
BREAST, and lung. The developing fetus also pro-
duces 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 CANCERtreatment 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, andCOLORECTAL CANCER. Other significant car-
cinogens 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 sun-
light (ultraviolet) or ionizing radiation such as
X-RAYand 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
MEDICATIONSand estrogen-containing drugs, may
cause cancer. Others are hazardous at nearly any
exposure level. CHEMOTHERAPYdrugs, which effec-
tively treat and cure many types of cancer, are
themselves carcinogenic for certain types of
LEUKEMIAand LYMPHOMA. RADIATION THERAPYas well
increases the risk for subsequent cancers, depend-
ing on the site of irradiation. Pathogens such as
viruses and BACTERIAcause 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 reg-
ulations provide guidelines for occupational expo-
sure 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 HEPATITISB VIRUS
HUMAN PAPILLOMAVIRUS(HPV) iodine-131
ionizing radiation methyl chloride
radon sunlight
tobacco vinyl chlorideSee 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 (lin-
ing of the internal body cavities). Carcinoma is the
most common form of cancer. A carcinoma gener-
ally carries the name of the tissue or site of its ori-
gin; 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.TYPES OF CARCINOMA
Tumor Location
ADENOCARCINOMA glandular tissue
basal cell carcinoma SKIN
intraductal carcinoma BREAST
large-cell carcinoma lung
lobular carcinoma BREAST
small-cell carcinoma lung
squamous cell carcinoma skin, mucous membranes374 Cancer