CARCINOMA IN SITU
fumes and is produced by inefficient
burning of coal, gas, or oil.
Carbon monoxide is toxic because it
carrying molecule in red blood cells),
w hich prevents the blood from carry-
ing oxygen to the body tissues. As a
result, the tissues are deprived of oxy-
initial symptoms of acute high-level
dizziness, headache, nausea, and faint-
ness. Continued inhalation of the gas
may lead to loss of consciousness, per-
manent brain damage, and even death.
Low-level exposure to carbon m onox-
ide over a period of time may cause
fatigue, nausea, diarrhoea, abdominal
pain, and general malaise.
carbon tetrachloride (CQ
A colourless, poisonous, volatile chem-
ical w ith a characteristic odour. Carbon
of one carbon
atom linked to four chlorine atoms and
has the chemical formula CCl4. Former-
ly used in domestic dry-cleaning fluids,
its use is now restricted to industry.
Carbon tetrachloride is an extremely
dangerous chemical, and it can cause
dizziness, confusion, and liver and kid-
ney damage if a significant amount of
the chemical is inhaled or swallowed.
A cluster of interconnected
inflamed hair roots).
Carbuncles are usually caused by infec-
tion with the bacterium S
. The back of the neck and the
buttocks are the most common sites.
The swellings mainly affect people with
reduced immunity, particularly those
Treatment is usually with an
In addition, the application of
may encourage the pus-
w hich relieves pain. Occasionally, in ci-
removal of the core of the carbuncle)
may be necessary if a carbuncle is per-
sistent, and drainage and healing have
not occurred spontaneously.
Any agent that is capable of causing
such as tobacco smoke, high-
or asbestos fibres.
Chemicals form the largest group of
carcinogens. Major types include poly-
cyclic aromatic hydrocarbons (PAHs),
w hich occur in tobacco smoke, pitch,
tar fumes, and soot. Exposure to PAHs
may lead to cancer of the respiratory
system or skin. In addition, certain aro-
matic amines used in the chemical and
rubber industries may cause bladder
cancer after prolonged exposure.
The best-known physical carcinogen is
high-energy radiation, such as nuclear
Radiation may also
in sunlight. Another known physical
carcinogen is asbestos
Exposure to radiation may cause can-
cerous changes in cells, especially in
cells that divide quickly; for example
changes in the
blood cells in the bone marrow causes
The level of risk depends on
the dosage and duration of exposure
to the carcinogen. Over many years,
exposure to ultraviolet radiation in sun-
light can cause skin cancer.
Only a few biological agents are known
to cause cancer in humans. S
, one of the blood flukes
can cause cancer of the
bladder; and A
, a fungus
that produces the poison
stored peanuts and grain, is believed to
cause liver cancer.
Viruses that are associated with can-
cer include some strains of the human
papilloma virus, w hich are linked to
cancer of the cervix; the hepatitis B and
C viruses, w hich are linked to liver can-
cer; and some types of herpes virus,
w hich are associated with
AVOIDANCE OF CARCINOGENS
In industry, known carcinogens may be
banned. Alternatively, as in the nuclear
industry and in hospital X-ray depart-
ments, they may be allowed only if
exposure to them is strictly limited,
and if regular medical screening is pro-
vided for workers using them.
Outside industry, people are exposed
to very few known, unavoidable, high-
risk carcinogens. Any substance that
could possibly be carcinogenic, such as
a food additive, a cosmetic, or a chem i-
cal for use in drugs, must be carefully
screened by an official body (such as
the Medicines Control Agency, w hich
assesses drugs in the UK) before it is
allowed to be manufactured.
The development of a
the action of
cause cancer) on normal cells.
Carcinogens are believed to alter the
in cells, particularly in
(genes that control the
division of cells). An altered cell divides
abnormally fast, passing on the genetic
changes to all of its offspring cells.
Thus, a group of cells is established that
is not affected by the body’s normal
restraints on growth.
A rare condition caused by an intestinal
or lung tumour,
called a carcinoid,
w hich secretes excessive amounts of
and often also
Carcinoid syndrome is characterized by
bouts of facial flushing, diarrhoea, and
wheezing, but symptoms usually occur
only if the tumour has spread to the
liver or has arisen in a lung.
Carcinoid tumours in the intestine,
lung, and, more rarely, the liver are
sometimes removed surgically, but, in
most cases, surgery is unlikely to be of
benefit. In these circumstances, symp-
toms may be relieved by drugs such as
growth of the tumour.
A type of hormone-secreting cancerous
tumour. Carcinoids most often occur in
the small intestine or rectum but occa-
sionally also develop in the lungs. (See
Any cancerous tumour (see
arises from cells in the covering surface
layer or lining membrane of an organ.
A carcinoma is distinguished from a
w hich is a cancer arising in
bone, muscle, or connective tissue. The
most common cancers of the lungs,
breast, stomach, skin, cervix,
and rectum are carcinomas.
carcinoma in situ
The earliest, usually curable, stage of a
cancer. In this stage, the disease has not
yet spread from the surface layer of
cells in an organ or other tissue.