From the NCI statements below, the following definition of a cancer
cluster emerges: a cancer cluster may be suspected when cases of
the "same or related cancer(s)" are reported in numbers that
are "greater than expected"...within a group of people, a geographic
area, or a period of time." There are several issues that arise from
this statement.

First, what do we mean by the "same or related cancer"? For example,
what is the "same cancer"? Do we mean a specific cell type within a
cancer grouping, e.g., B-cell acute lymphocytic leukemia, or do we
mean all acute lymphocytic leukemias? Is childhood non-Hodgkin's
lymphoma a cancer that is "related" to childhood ALL? Do we mean
by "related cancers" cancers that have a similar etiology? For
example, if we suspect a situation where a population is exposed to
ionizing radiation, would it make sense to include in a cluster all
the cancers that can be caused by ionizing radiation exposure? The
answer to all these questions depends on the investigator's or
community's hypothesis concerning the cluster and the exposure
situation. This hypothesis can be stated up front and transparently,
or it can be hidden and unconscious (or somewhere in-between). But
the key point I want to make is that the decision as to what cancers
to include in or exclude from a cluster involves an hypothesis -
whether it is stated explicitly or not, whether it is conscious or
not (or whether it is a rote or knee-jerk hypothesis or not). If you
have an hypothesis that a particular exposure (e.g., contaminated
drinking water) may be behind the cluster, then it makes sense to
include in the cluster those cancers that could be caused by that
exposure. (Or, if you know or suspect that the exposure causes a
specific cell type within a cancer grouping, then you might restrict
the cluster to that cell type.) Alternatively, if you think there is
no unique exposures happening in the community and that any cluster
would be due to a bias (e.g., confounding by age) or chance, then you
might take the easy route and define the cluster in terms of the
organ/tissue affected (e.g., all leukemias, or all childhood
leukemias) since your hypothesis denies that there is an exposure
etiology.

The next issue is what do we mean by "greater than expected"? Do we
mean that the rate ratio or odds ratio is greater than 1.0 (or the
SMR is greater than 100)? Does it have to be "statistically
significant"? Should we equate "statistical significance"
with "public health significance"? What type 1 error and type 2
error are we assuming when we do statistical significance testing and
why? (For example, why should we set the type 1 error at .05 and the
type 2 error at .20 - in other words, why are we more worried about a
false positive than a false negative?) These are decisions that I
believe require full community involvement in the deliberation, and
that require justification. Of course, what virtually always happens
is that the investigator (or health agency) alone arbitrarily makes
these decisions and hides behind an unexamined and false notion
of "scientific tradition" or "good science".

Next, there is the issue of deciding how to define the "group of
people", "geographic area", and "period of time". As with the
definition of the cluster (i.e., what to include in or exclude from
the cluster), these decisions are based on an implicit or explicit
hypothesis concerning the cluster and the exposure situation. These
decisions are also strongly influenced by what data are available and
how much resources the investigator is willing to spend in the
investigation.

So to answer your question, how a cluster is defined is a decision
that is based on an explicit or implicit (conscious or unconscious or
rote) hypothesis concerning the disease and exposure situation in the
community (or occupational cohort). The best way to define a cluster
is to have a clear exposure hypothesis that is developed with the
full participation of the affected community. The other decisions
that are involved in such an investigation should likewise be
deliberated and determined with the full participation of the
affected community. I believe that the Woburn childhood cancer
cluster investigation came the closest to fitting these requirements
and that is why it was successful.

Frank J. Bove, Sc.D
Senior Epidemiologist
Division of Health Studies
Agency for Toxic Substances and Disease Registry (ATSDR)/CDC
Mailstop E-31
1600 Clifton Rd NE
Atlanta, GA 30333
(404) 498-0557
(404) 498-0077 fax
fbove@...

--- In NationalDiseaseClustersAlliance@yahoogroups.com, Agnes
Reynolds <merbenzrn@...> wrote:
>
> Just a thought.... I understand the disease cluster protocols are
being worked on...(YAY!!)
> As usual, I have a question...this is regard to cancer clusters.
> It is a common understanding that only one type of cancer should
be investigated as part of a cluster.... (as stated in this
document). I have understood this concept to be the norm, but do our
NDCA epidemiologists truly agree with this statement? I have heard
debate on this topic in the past and am wondering about whether or
not this will be the case in our own community investigations?
>
> Just curious...Comments welcome from all.
>
> Agnes
>
>
>
>
> Send to
Printer Reviewed:
10/05/2006
> Cancer Clusters
> Key Points
> Cancer clusters may be suspected when people report that several
family members, friends, neighbors, or coworkers have been diagnosed
with the same or related cancer(s) (see Defining Disease Clusters
section).
> Epidemiologists (scientists who study the frequency,
distribution, causes, and control of diseases in populations)
investigate suspected cancer clusters (see Facts About Cancer
Clusters section).
> Some amount of clustering may occur simply by chance (see Facts
About Cancer Clusters section).
> A suspected cancer cluster may be reported to a state or local
health department or state cancer registry (see Reporting Suspected
Cancer Clusters section).
> Other resources may provide additional information about cancer
clusters, cancer incidence and mortality, and environmental risk
factors for cancer (see Resources section).
>
> Defining Disease Clusters A disease cluster is the occurrence
of a greater than expected number of cases of a particular disease
within a group of people, a geographic area, or a period of time.
Clusters of diseases have concerned scientists for centuries. Some
recent disease clusters include the initial cases of a rare type of
pneumonia among homosexual men in the early 1980s that led to the
identification of the human immunodeficiency virus (HIV) and acquired
immunodeficiency syndrome (AIDS); the outbreak in 2003 of a
respiratory illness, later identified as severe acute respiratory
syndrome (SARS), caused by a previously unrecognized virus; and
periodic outbreaks of food poisoning caused by eating food
contaminated with bacteria.
> Cancer clusters may be suspected when people report that several
family members, friends, neighbors, or coworkers have been diagnosed
with the same or related cancer(s). In the 1960s, one of the best
known cancer clusters emerged, involving many cases of mesothelioma
(a rare cancer of the lining of the chest and abdomen). Researchers
traced the development of mesothelioma to exposure to asbestos, a
fibrous mineral that was used heavily in shipbuilding during World
War II and has also been used in manufacturing industrial and
consumer products. Working with asbestos is the major risk factor
(something that may increase the chance of developing a disease) for
mesothelioma.
> Facts About Cancer Some concepts about cancer can be helpful
when trying to understand suspected cancer clusters:
>
> Cancer is the uncontrolled growth and spread of abnormal cells
anywhere in the body. However, cancer is not just one disease; it is
actually an umbrella term for at least 100 different but related
diseases.
>
> Each type of cancer has certain known and/or suspected risk
factors associated with it.
>
> Cancer is not caused by injuries, nor is it contagious. It
cannot be passed from one person to another like a cold or flu
virus.
>
> Cancer is almost always caused by a combination of factors
that interact in ways that are not yet fully understood.
>
>
> Carcinogenesis (the process by which normal cells are
transformed into cancer cells) involves a series of changes within
cells that usually occur over many years. More than 10 years can go
by between the exposure to a carcinogen (any substance that causes
cancer) and a diagnosis of cancer, which makes it difficult to
pinpoint the cause of that cancer.
>
>
> Cancer is more likely to occur as people get older; because
people are living longer, more cases of cancer can be expected in the
future. This increased life expectancy may create the impression that
cancer is becoming much more common, even though an increase in the
number of cases of cancer is related in large part to the growing
number of elderly people in the population.
>
>
> Some racial and ethnic groups have higher rates of cancer than
other racial and ethnic groups. Such differences may be due to
multiple factors, such as late stage of disease at diagnosis,
barriers to health care access, history of other diseases, biologic
and genetic differences, health behaviors, and other risk factors.
>
> Cancer, in general, is common. More than 17 million new cases
of cancer have been diagnosed since 1990.
>
> Facts About Cancer Clusters
> Reported disease clusters of any kind, including suspected cancer
clusters, are investigated by epidemiologists (scientists who study
the frequency, distribution, causes, and control of diseases in
populations). Epidemiologists use their knowledge of diseases,
environmental science, lifestyle factors, and biostatistics to try to
determine whether a suspected cluster represents a true excess of
cancer cases. Epidemiologists have identified certain circumstances
that may lead them to suspect a potential common source or cause of
cancer among people thought to be part of a cancer cluster. A
suspected cancer cluster is more likely to be a true cluster, rather
than a coincidence, if it involves one or more of the following
factors:
>
> A large number of cases of one type of cancer, rather than
several different types.
>
> A rare type of cancer, rather than common types.
>
> An increased number of cases of a certain type of cancer in an
age group that is not usually affected by that type of cancer.
>
> Before epidemiologists can assess a suspected cancer cluster
accurately, they must determine whether the type of cancer involved
is a primary (original) cancer or a cancer that has metastasized
(spread from another organ). This is important to know because
scientists consider only the primary cancer when they investigate a
possible cancer cluster. Epidemiologists also try to establish
whether the suspected exposure has the potential to cause the
reported cancer, based on what is known about that cancer's likely
causes and about the cancer-causing potential of the exposure.
After developing a case definition (the guidelines that determine
whether the cases being investigated are related to the cluster),
epidemiologists must identify the time period of concern and the
population at risk. They then calculate the expected number of cases
and compare that number with the observed number of cases.
Epidemiologists must show that the number of cancer cases that have
occurred is
> significantly greater than the expected number of cases, given the
age, gender, and racial distribution of the group of people at risk
of developing the disease.
> Epidemiologists must also determine if the cancer cases could
have occurred by chance. They often test for "statistical
significance," which is a mathematical measure of the difference
between groups. The difference is said to be statistically
significant if it is greater than what would be expected to happen by
chance alone. In common practice, a statistically significant finding
means that the probability that the observed number of cases could
have happened by chance alone is 5 percent or less. For instance, if
one examines the number of cancer cases in 100 neighborhoods, and
cancer cases are occurring by chance alone, one should expect to find
about five neighborhoods with a statistically significant elevation
in the number of cancer cases. In other words, some amount of
clustering within the same family or neighborhood may occur simply by
chance.
> Accurately defining the group of people who should be
considered "at risk" is important when investigating a possible
cancer cluster. One of the greatest problems in defining clusters is
the tendency to expand the geographic borders of the cluster to
include additional cases of the suspected disease as they are
discovered. The tendency to define the borders of a cluster on the
basis of where known cases are located, rather than to first define
the population and geographic area and then determine if the number
of cancers is excessive, creates many "clusters" that are not real.
> Epidemiologists must also consider that a confirmed cancer
cluster may not be the result of any single, external cause or
hazard. A cancer cluster could be the result of chance, an error in
the calculation of the expected number of cancer cases, or
differences in the case definition between observed and expected
cases. Moreover, because people change where they live from time to
time, it can be difficult for epidemiologists to identify previous
exposures and find the medical records that are needed to determine
the kind of cancer a person had—or if it was cancer at all.
> Because a variety of factors often work together to create the
appearance of a cluster where nothing abnormal is occurring, most
reports of suspected cancer clusters are not shown to be true
clusters. Many reported clusters do not include enough cases for
epidemiologists to arrive at any conclusions. Sometimes, even when a
suspected cluster has enough cases for study, a greater than expected
number of cases cannot be demonstrated. Other times, epidemiologists
find a true excess of cases, but they cannot find an explanation for
it. For example, a suspected carcinogen may cause cancer only under
certain circumstances, making its impact difficult to detect.
> Genetics and Environment
> Because most cancers are thought to be caused by a combination of
factors related to genetics and environment (including behavior and
lifestyle), studies of suspected cancer clusters usually focus on
these two issues. Genetic factors are inherited, that is, passed from
parents to children. However, establishing a genetic-environmental
interaction (significant and valid evidence that a specific genetic
factor leads to an increased chance that a particular environmental
exposure will result in cancer) requires studies of large populations
over long periods of time. Researchers are just beginning to learn
about the roles genetics and environmental exposures play in
carcinogenesis. Some of their discoveries are outlined below:
> Genetics
>
> All cancers develop because of genetic alterations of one kind
or another. An alteration is a change or mutation in the physical
structure of a gene that interferes with the gene's normal
functions.
>
> Some genetic alterations that increase the risk of cancer are
present at birth in the genes of all cells in the body, including
reproductive cells. These changes, which are called germline
mutations, can be passed from parent to child. This type of
alteration is known as an inherited susceptibility; most cancers are
not due to an inherited susceptibility.
>
>
> Most cancers result from genetic changes that occur after birth
during one's lifetime. Genetic changes can occur in any cell that
divides. These genetic changes are called somatic alterations.
>
>
> Familial cancer clusters (cancer that occurs in families more
often than would be expected by chance) have been reported for many
types of cancer. Because cancer is a common disease, it is not
unusual for several cases to occur within a family. Familial cancer
clusters are sometimes linked to inherited susceptibility, but
environmental factors and chance may also be involved.
>
>
> Having an inherited susceptibility for a type of cancer does not
necessarily mean that the individual will be diagnosed with the
cancer; it means the chance of developing cancer increases if other
factors that promote the development of cancer are present or are
encountered later.
>
> Environment
>
> The term environment includes not only air, water, and soil, but
also substances and conditions in the home and workplace. It also
includes diet; the use of tobacco, alcohol, or drugs; exposure to
chemicals; and exposure to sunlight and other forms of radiation.
>
>
> People are exposed to a variety of environmental factors for
varying lengths of time, and these factors interact in ways that are
still not fully understood. Further, individuals have varying levels
of susceptibility to these factors.
>
>
> Hazardous substances are often found in higher levels in the
workplace than in the general environment. For this reason, some
workers may have greater and longer exposures to such substances than
the general population. Findings of higher than expected numbers of
cancer cases among workers in particular occupations or industries
provide important leads regarding causes of cancer among the general
public. In fact, occupational studies (studies of specific groups of
workers) have identified many specific cancer-causing substances and
have provided the motivation to find ways to reduce or eliminate
exposures in the workplace and elsewhere.
> Reporting Suspected Cancer Clusters
> A suspected cancer cluster may be reported to a state or local
health department or state cancer registry. State and local health
departments and cancer registries use established criteria to
investigate reports of cancer clusters. When a suspected cancer
cluster is first reported, the investigating department or agency
gathers information and gives the inquirer general information about
cancer clusters. Although investigators may use different processes,
most follow a basic procedure in which increasingly specific
information is obtained and analyzed in stages. Investigators are
likely to request the following:
> Information about the potential cluster: type(s) of cancer,
number of cases, suspected exposure(s), and geographic area/time
period of concern.
>
> Information about each person with cancer in the potential
cluster: name, address, telephone number, gender, race, age,
occupation(s), as well as area(s) lived in/length of time.
>
> Information about each case of cancer: type of cancer, date of
diagnosis, age at diagnosis, possible causes, metastatic sites, and
physician contact.
> Most reports of suspected cancer clusters are resolved at this
initial contact because concerned individuals realize that what
seemed like a cancer cluster is not a true cluster. If further
evaluation is needed, epidemiologists will take the following steps
to investigate a possible cancer cluster:
> Attempt to verify the reported cases by contacting patients and
relatives and obtaining medical records.
>
> Compare the number of cases in the suspected cancer cluster with
information in census data and cancer registries to determine if
there is a higher than expected number of cases.
>
> Review the scientific literature to establish whether the
reported cancer(s) has been linked to the suspected exposure.
>
> Work with Federal agencies, if necessary, to gather additional
information to help decide whether to conduct a comprehensive
epidemiological study.
> Resources
> The following resources may provide additional information about
cancer clusters, cancer incidence (the number of new cases) and
mortality (the number of deaths), and environmental risk factors for
cancer:
> Local and state health departments are listed under such
headings as "health department" and "public health commission" in the
blue pages of Government listings in telephone books. In addition,
links to state and selected local health department Web sites can be
found at http://www.cdc.gov/nceh/clusters/statelocal.htm on the
Internet.
>
> State cancer registries collect data on cancer incidence and
mortality. The data in these registries can be used to compare
expected cancer rates in certain categories, such as geographic area,
gender, age, or racial group, with rates reported in a suspected
cancer cluster to determine whether there is a true excess of cases.
State cancer registries are listed under such headings as "health
department" and "public health commission" in the blue pages of
Government listings in telephone books. Contact information for state
cancer registries can also be found at
http://apps.nccd.cdc.gov/cancercontacts/npcr/contacts.asp on the
Internet.
>
> The Centers for Disease Control and Prevention's (CDC)
National Center for Environmental Health (NCEH) cancer clusters Web
site provides links to cancer cluster resources, answers to
frequently asked questions, and an online inquiry form. NCEH can be
contacted at:
> Address: Division of Environmental Hazards and Health
Effects
> National Center for Environmental Health
> Centers for Disease Control and Prevention
> Re: Cancer Clusters
> Mail Stop F–52
> 4770 Buford Highway
> Atlanta, GA 30341
> Telephone: 1–800–232–4636 (1–888–CDC–INFO) (toll-free) E-
mail: cdcinfo@...
> Internet Web site: http://www.cdc.gov/nceh/clusters/
>
> The CDC's National Institute for Occupational Safety and Health
(NIOSH) conducts research and makes recommendations for the
prevention of work-related disease and injury. Information about
possible workplace cancer clusters and how they are evaluated is
available on NIOSH's Occupational Cancer Web page at
http://www.cdc.gov/niosh/topics/cancer/ on the Internet. NIOSH's
Health Hazard Evaluation (HHE) Program investigates potentially
hazardous working conditions, including suspected cancer clusters,
when employers, authorized employee representatives, or employees
request it. The HHE Program can be contacted at:
Address: Hazard Evaluation and Technical Assistance Branch
> NIOSH
> Mail Stop R–9
> 4676 Columbia Parkway
> Cincinnati, OH 45226
> Telephone: 1–800–356–4674 (1–800–35–NIOSH) (toll-free)
> Internet Web site: http://www.cdc.gov/niosh/hhe
>
> The Agency for Toxic Substances and Disease Registry (ATSDR), an
agency of the U.S. Department of Health and Human Services (DHHS),
conducts public health assessments of waste sites, performs health
consultations concerning specific hazardous substances, maintains
health surveillance and registries, responds to emergency releases of
hazardous substances, and provides education and training concerning
hazardous substances. Contact information for ATSDR regional offices
can be found at http://www.atsdr.cdc.gov/DRO/dro_contact.html on the
Internet. The ATSDR can be contacted at: Telephone: 1–
800–232–4636 (1–800–CDC–INFO)
> 1–888–232–6348
> Internet Web site: http://www.atsdr.cdc.gov
>
> The National Institute of Environmental Health Sciences (NIEHS),
a part of the National Institutes of Health (NIH), studies how
environmental exposures, genetic susceptibility, and age interact to
affect an individual's health. The NIEHS can be contacted
at: Address: The National Institute of Environmental
Health Sciences
> Post Office Box 12233
> Research Triangle Park, NC 27709
> Telephone: 919–541–3345
> Internet Web site: http://www.niehs.nih.gov
>
> The Occupational Safety and Health Administration's (OSHA)
Office of Occupational Medicine performs workplace-related case
evaluations and cluster investigations, including medical record
review, employee interviews, and medical screening activities. OSHA
can be contacted at:
> Address: Office of Occupational Medicine
> Occupational Safety and Health Administration
> U.S. Department of Labor
> Room N3457
> 200 Constitution Avenue, NW.
> Washington, D.C. 20210
> Telephone: 202–693–2323
> Internet Web site: http://www.osha.gov/dts/oom/index.html
>
> The Where You Live Web page, which is managed by the U.S.
Environmental Protection Agency (EPA), allows users to enter a ZIP
Code and choose from four databases to retrieve environmental
information about a community or to locate a regional office. This
resource is available at http://www.epa.gov/epahome/whereyoulive.htm
on the Internet.
>
>
> The National Cancer Institute (NCI), another component of the
NIH, has the Cancer Mortality Maps and Graphs Web site, which
provides interactive maps, graphs, text, tables, and figures showing
geographic patterns and time trends of cancer death rates for the
time period 1950–94 for more than 40 cancers. It also provides
interactive mortality charts and graphs, customizable mortality maps,
and links to related domestic and international Web sites, including
a link to the online publication of NCI's Atlas of Cancer Mortality
in the United States: 1950–94. The NCI's Cancer Mortality Maps and
Graphs Web site can be accessed at
http://www3.cancer.gov/atlasplus/new.html on the Internet.
> # # #
> Related Resources
> Publications (available at http://www.cancer.gov/publications)
> National Cancer Institute Fact Sheet 6.7, Cancer: Questions and
Answers 1
> Cancer and the Environment: What You Need To Know, What You Can
Do 2
> What You Need To Know About™ Cancer 3
>
>
> National Cancer Institute (NCI) Resources
>
> Cancer Information Service (toll-free)
> Telephone: 1–800–4–CANCER (1–800–422–6237)
> TTY: 1–800–332–8615
>
>
> Online
> NCI's Web site: http://www.cancer.gov
> LiveHelp, NCI's live online assistance:
> https://cissecure.nci.nih.gov/livehelp/welcome.asp
>
>
> Glossary Termsabdomen (AB-doh-men) The area of the body that
contains the pancreas, stomach, intestines, liver, gallbladder, and
other organs. abnormal Not normal. An abnormal lesion or growth may
be cancerous, premalignant (likely to become cancer), or benign.
acquired immunodeficiency syndrome (uh-KWY-erd IH-myoo-noh-dih-FIH-
shun-see SIN-drome) AIDS. A disease caused by human
immunodeficiency virus (HIV). People with acquired immunodeficiency
syndrome are at an increased risk for developing certain cancers and
for infections that usually occur only in individuals with a weak
immune system. Also called AIDS. alteration A change resulting in
something that is different from the original. asbestos (as-BES-
tus) A natural material that is made of tiny fibers. Asbestos can
cause several serious diseases, including cancer. bacteria (bak-TEER-
ee-uh) A large group of single-cell microorganisms. Some cause
infections and disease in animals and humans. The singular of
> bacteria is bacterium. cancer (KAN-ser) A term for diseases in
which abnormal cells divide without control. Cancer cells can invade
nearby tissues and can spread to other parts of the body through the
blood and lymph systems. There are several main types of cancer.
Carcinoma is cancer that begins in the skin or in tissues that line
or cover internal organs. Sarcoma is cancer that begins in bone,
cartilage, fat, muscle, blood vessels, or other connective or
supportive tissue. Leukemia is cancer that starts in blood-forming
tissue such as the bone marrow, and causes large numbers of abnormal
blood cells to be produced and enter the blood. Lymphoma and multiple
myeloma are cancers that begin in the cells of the immune system.
Central nervous system cancers are cancers that begin in the tissues
of the brain and spinal cord. cancer cluster (KAN-ser KLUS-ter) The
occurrence of a larger-than-expected number of cases of cancer within
a group of people in a geographic area over
> a period of time. carcinogen (kar-SIN-o-jin) Any substance that
causes cancer. carcinogenesis The process by which normal cells are
transformed into cancer cells. cell (sel) The individual unit that
makes up the tissues of the body. All living things are made up of
one or more cells. diagnosis The process of identifying a disease
by the signs and symptoms. diet The things a person eats and
drinks. drug Any substance, other than food, that is used to
prevent, diagnose, treat or relieve symptoms of a disease or abnormal
condition. Also refers to a substance that alters mood or body
function, or that can be habit-forming or addictive, especially a
narcotic. familial cancer Cancer that occurs in families more often
than would be expected by chance. These cancers often occur at an
early age, and may indicate the presence of a gene mutation that
increases the risk of cancer. They may also be a sign of shared
environmental or lifestyle factors. fibrous Containing
> or resembling fibers. gene The functional and physical unit of
heredity passed from parent to offspring. Genes are pieces of DNA,
and most genes contain the information for making a specific protein.
genetic (jeh-NEH-tik) Inherited; having to do with information that
is passed from parents to offspring through genes in sperm and egg
cells. genetic susceptibility An inherited increase in the risk of
developing a disease. Also called genetic predisposition. germline
mutation (...myoo-TAY-shun) A gene change in the body's
reproductive cells (egg or sperm) that becomes incorporated into the
DNA of every cell in the body of offspring; germline mutations are
passed on from parents to offspring. Also called hereditary mutation.
human immunodeficiency virus (HYOO-mun ih-MYOO-noh-dih-FIH-shun-see
VY-rus) HIV. The cause of acquired immunodeficiency syndrome
(AIDS). Also called HIV. incidence The number of new cases of a
disease diagnosed each year. inherited
> (in-HAYR-it-ed) Transmitted through genes that have been passed
from parents to their offspring (children). mesothelioma (meh-zuh-
thee-lee-OH-muh) A benign (noncancerous) or malignant (cancerous)
tumor affecting the lining of the chest or abdomen. Exposure to
asbestos particles in the air increases the risk of developing
malignant mesothelioma. metastasize (meh-TAS-tuh-size) To spread
from one part of the body to another. When cancer cells metastasize
and form secondary tumors, the cells in the metastatic tumor are like
those in the original (primary) tumor. metastatic (meh-tuh-STA-tik)
Having to do with metastasis, which is the spread of cancer from one
part of the body to another. mineral A nutrient required to
maintain health. mutation (myoo-TAY-shun) Any change in the DNA of
a cell. Mutations may be caused by mistakes during cell division, or
they may be caused by exposure to DNA-damaging agents in the
environment. Mutations can be harmful, beneficial, or
> have no effect. If they occur in cells that make eggs or sperm,
they can be inherited; if mutations occur in other types of cells,
they are not inherited. Certain mutations may lead to cancer or other
diseases. National Cancer Institute NCI. The National Cancer
Institute, part of the National Institutes of Health of the United
States Department of Health and Human Services, is the Federal
Government's principal agency for cancer research. NCI conducts,
coordinates, and funds cancer research, training, health information
dissemination, and other programs with respect to the cause,
diagnosis, prevention, and treatment of cancer. Access the NCI Web
site at http://www.cancer.gov. Also called NCI. National Institutes
of Health NIH. A federal agency in the U.S. that conducts
biomedical research in its own laboratories; supports the research of
non-Federal scientists in universities, medical schools, hospitals,
and research institutions throughout the country and abroad;
> helps in the training of research investigators; and fosters
communication of medical information. Access the National Institutes
of Health Web site at http://www.nih.gov. Also called NIH. organ A
part of the body that performs a specific function. For example, the
heart is an organ. physician Medical doctor. pneumonia (noo-MONE-
ya) An inflammatory infection that occurs in the lung. primary
tumor The original tumor. radiation (RAY-dee-AY-shun) Energy
released in the form of particles or electromagnetic waves. Common
sources of radiation include radon gas, cosmic rays from outer space,
and medical x-rays. reproductive cell An egg or sperm cell. Each
mature reproductive cell carries a single set of 23 chromosomes. risk
factor Something that may increase the chance of developing a
disease. Some examples of risk factors for cancer include age, a
family history of certain cancers, use of tobacco products, certain
eating habits, obesity, lack of exercise, exposure
> to radiation or other cancer-causing agents, and certain genetic
changes. screening Checking for disease when there are no symptoms.
significant In statistics, describes a mathematical measure of
difference between groups. The difference is said to be significant
if it is greater than what might be expected to happen by chance
alone. Also called statistically significant. stage The extent of a
cancer in the body. Staging is usually based on the size of the
tumor, whether lymph nodes contain cancer, and whether the cancer has
spread from the original site to other parts of the body.
statistically significant Describes a mathematical measure of
difference between groups. The difference is said to be statistically
significant if it is greater than what might be expected to happen by
chance alone. Also called significant. tobacco (tuh-BA-koh) A plant
with leaves that have high levels of the addictive chemical nicotine.
The leaves may be smoked (in cigarettes, cigars,
> and pipes), applied to the gums (as dipping and chewing tobacco),
or inhaled (as snuff). Tobacco leaves also contain many cancer-
causing chemicals, and tobacco use and exposure to secondhand tobacco
smoke have been linked to many types of cancer and other diseases.
The scientific name is Nicotiana tabacum. virus (VY-rus) A
microorganism that can infect cells and cause disease.
>
> Table of Links 1
http://cancer.gov/cancertopics/factsheet/Sites-Types/general 2
http://cancer.gov/images/Documents/5d17e03e-b39f-4b40-a214-
e9e9099c4220/Cancer%
> 20and%20the%20Environment.pdf 3
http://cancer.gov/cancerinfo/wyntk/overview
>