Transcript What Is Cancer?

Industrial chemistry
Carcinogens
Kazem.R.Abdollah
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What Is Cancer?
• Cancer is a class of diseases characterized by outof-control cell growth. There are over 100
different types of cancer, and each is classified by
the type of cell that is initially affected.
• Cancer harms the body when damaged cells
divide uncontrollably to form lumps or masses of
tissue called tumors (except in the case of
leukemia where cancer prohibits normal blood
function by abnormal cell division in the blood
stream).
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More dangerous, or malignant, tumors form
when two things occur:
1. a cancerous cell manages to move
throughout the body using the blood or
lymph systems, destroying healthy tissue in
a process called invasion
2. that cell manages to divide and grow,
making new blood vessels to feed itself in a
process called angiogenesis.
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What causes cancer?
• Cancer is ultimately the result of cells that
uncontrollably grow and do not die. Normal cells
in the body follow an orderly path of growth,
division, and death. Programmed cell death is
called apoptosis, and when this process breaks
down, cancer begins to form.
• Unlike regular cells, cancer cells do not
experience programmatic death and instead
continue to grow and divide. This leads to a mass
of abnormal cells that grows out of control.
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How is cancer classified?
• There are five broad groups that are used to classify cancer.
1) Carcinomas are characterized by cells that cover internal and
external parts of the body such as lung, breast, and colon cancer.
2) Sarcomas are characterized by cells that are located in bone,
cartilage, fat, connective tissue, muscle, and other supportive
tissues.
3) Lymphomas are cancers that begin in the lymph nodes and
immune system tissues.
4) Leukemias are cancers that begin in the bone marrow and often
accumulate in the bloodstream.
5) Adenomas are cancers that arise in the thyroid, the pituitary
gland, the adrenal gland, and other glandular tissues.
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Carcinogens
• Carcinogens are a class of substances that are
directly responsible for damaging DNA, promoting or
aiding cancer. Tobacco, asbestos, arsenic, radiation
such as gamma and x-rays, the sun, and compounds
in car exhaust fumes are all examples of carcinogens.
When our bodies are exposed to carcinogens, free
radicals are formed that try to steal electrons from
other molecules in the body. Theses free radicals
damage cells and affect their ability to function
normally.
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What is a carcinogen?
• Some of these changes may be inherited from our parents, while
others may be caused by outside exposures, which are often
referred to as environmental factors. Environmental factors can
include a wide range of exposures, such as:
1.
2.
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4.
5.
6.
Lifestyle factors (nutrition, tobacco use, physical activity, etc.)
Naturally occurring exposures (ultraviolet light, radon gas,
infectious agents, etc.)
Medical treatments (chemotherapy, radiation, immune systemsuppressing drugs, etc.)
Workplace exposures
Household exposures
Pollution
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How do researchers determine if
something is a carcinogen?
• Testing to see if something can cause cancer is
often difficult. It is not ethical to test a
substance by exposing people to it and seeing
if they get cancer from it. That’s why scientists
must use other types of tests, which may not
always give clear answers.
1. Lab studies
2. Studies in people
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Lab studies
• Although lab studies alone can't always predict if a
substance will cause cancer in people, virtually all
known human carcinogens that have been adequately
tested also cause cancer in lab animals. In many cases,
carcinogens are first found to cause cancer in lab
animals and are later found to cause cancer in people.
• Most studies of potential carcinogens expose the lab
animals to doses that are much higher than common
human exposures. This is so that cancer risk can be
detected in relatively small groups of animals. It is not
always clear if the results from animal studies will be
the same for people as they are normally exposed to a
substance.
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Studies in people
• Another important way to identify carcinogens is through
epidemiologic studies, which look at human populations to
determine which factors might be linked to cancer. These
studies also provide useful information, but they have their
limits. Humans do not live in a controlled environment.
People are exposed to many substances at any given time,
including those they encounter at work, school, or home; in
the food they eat; and in the air they breathe. It's very
unlikely they know exactly what they've been exposed to or
that they would be able to remember all of their exposures
if asked by a researcher. And there are usually many years
(often decades) between exposure to a carcinogen and the
development of cancer. Therefore, it can be very hard to
definitely link any particular exposure to cancer.
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Who determines how carcinogens are
classified?
• Several agencies (national and international) are
responsible for determining the cancer-causing
potential of different substances.
 International Agency for Research on Cancer (IARC)
 National Toxicology Program (NTP)
 US Environmental Protection Agency (EPA)
 Other agencies and groups
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International Agency for
Research on Cancer
The International Agency for Research on Cancer (IARC)
is part of the World Health Organization (WHO). Its
major goal is to identify causes of cancer. The most
widely used system for classifying carcinogens comes
from the IARC. In the past 30 years, the IARC has
evaluated the cancer-causing potential of more than
900 likely candidates, placing them into one of the
following groups:
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Group 1: Carcinogenic to humans
Group 2A: Probably carcinogenic to humans
Group 2B: Possibly carcinogenic to humans
Group 3: Unclassifiable as to carcinogenicity in humans
Group 4: Probably not carcinogenic to humans
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Radiation
• Both Wilhelm Röntgen and Marie Curie died of cancer
caused by radiation exposure during their experiments.
• Not all types of electromagnetic radiation are
carcinogenic.
• Low-energy waves on the electromagnetic spectrum
are generally not, including radio waves, microwave
radiation, infrared radiation, and visible light.
• Higher-energy radiation, including ultraviolet radiation
(present in sunlight), x-rays, and gamma radiation,
generally is carcinogenic, if received in sufficient doses.
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Carcinogens in prepared food
• Cooking food at high temperatures, for example
broiling or barbecuing meats, can lead to the
formation of minute quantities of many potent
carcinogens that are comparable to those found
in cigarette smoke (i.e., benzopyrene) (Zheng et
al. 1998). Charring of food resembles coking and
tobacco pyrolysis and produces similar
carcinogens.
• There are several carcinogenic pyrolysis products,
such as polynuclear aromatic hydrocarbons,
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which are converted by human enzymes into
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