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Cancer is such a common disease that it is no surprise that
many families have at least a few members who have had cancer.
Sometimes, certain types of cancer seem to run in some families. This
can be caused by a number of factors. Often, family members have
certain risk factors in common, such as smoking, which can cause many
types of cancer. But in some cases the cancer is caused by an abnormal
gene that is being passed along from generation to generation. Although
this is often referred to as inherited
cancer, what is inherited is the abnormal gene that can lead to cancer,
not the cancer itself. Only about 5% to 10% of all cancers are
inherited. This document focuses on those cancers.
DNA, genes, and chromosomes
Cancer is a disease of abnormal gene function. Genes are pieces of
DNA (deoxyribonucleic acid). They contain the instructions on how to
make the proteins the body needs to function, when to destroy damaged
cells, and how to keep the cells in balance. Your genes control things
such as hair color, eye color, and height. They also can affect your
chance of getting certain diseases, such as cancer.
An abnormal change in a gene is called a mutation. The 2
types of mutations are inherited and acquired. Inherited gene mutations
are are passed from parent to child through the egg or sperm. These
mutations are in every cell in the body. But most mutations that occur
are not present in the egg or sperm. These mutations are called
somatic. Somatic mutations are acquired. at some point in the person's
life. This type of mutation occurs in one cell, and then is passed on
to any new cells that are the offspring of that cell.
Genes are found on chromosomes. Humans have 23 pairs of
chromosomes in each cell. We inherit one set of chromosomes from each
parent. Each chromosome can contain hundreds or thousands of genes that
are passed from the parents to the child. Every cell in your body has
all of the genes you were born with. Although all cells have the same
genes and chromosomes, different cells (or types of cells) may use
different genes. For example, muscle cells use a different set of genes
than skin cells use. The genes that the cell doesn't need are turned
off and not used. The genes that the cell is using are activated or
turned on.
Genes and cancer
Genes seem to have 2 major roles in cancer. Some, called oncogenes, can
cause cancer. Others, known as tumor
suppressor genes, stop cancer from developing or growing.
More information about oncogenes and tumor suppressor genes can be
found in our document, Oncogenes, Tumor Suppressor
Genes, and Cancer.
Oncogenes
are mutated forms of certain normal genes of the cell called proto-oncogenes.
Proto-oncogenes are often genes that normally control what kind of cell
it is and how often it grows and divides. When a proto-oncogene mutates
(changes) into an oncogene, it turns on or activates when it is not
supposed to be. When this occurs, the cell can grow out of control,
leading to cancer.
Tumor
suppressor genes are normal genes that slow down cell
division, repair DNA mistakes, and tell cells when to die (a process
known as apoptosis
or programmed cell death). When tumor suppressor genes don’t
work properly, cells can grow out of control, which can lead to cancer.
A tumor suppressor gene is like the brake pedal on a car. It
normally keeps the cell from dividing too quickly just as a brake keeps
a car from going too fast. When something goes wrong with the gene,
such as a mutation, cell division can get out of control.
An important difference between oncogenes and tumor suppressor
genes is that oncogenes result from the activation (turning
on) of proto-oncogenes, but tumor suppressor genes cause cancer when
they are inactivated
(turned off).
Even if you were born with healthy genes, some of them can
become changed (mutated) over the course of your life. These mutations
are known as sporadic or somatic, meaning they are not inherited.
Sporadic mutations cause most cases of cancer. These mutations are
thought to be caused by things that we are exposed to in our
environment, including cigarette smoke, radiation, hormones, and diet.
More gene mutations build up as we get older, leading to a higher risk
of cancer.
When someone has inherited an abnormal copy of a gene, their
cells already start out with one mutation. This makes it all the easier
(and quicker) for enough mutations to build up for a cell to become
cancer. That is why cancers that are inherited tend to occur earlier in
life than cancers of the same type that are not inherited.
When should I worry?
When many cases of cancer occur in a family, it is most often
due to chance or because family members have been exposed to a common
toxin, such as cigarette smoking. Less often, these cancers may be
caused by an inherited gene mutation. (These are called family cancer
syndromes.) Certain things make it more likely that an abnormal gene is
causing cancers in a family, such as
- Many cases of a rare type of cancer (like kidney cancer)
- Cancers occurring at younger ages than usual (like colon
cancer in a 20 year old)
- More than one type of cancer in a single person (like a
woman with both breast and ovarian cancer)
- Cancers occurring in both of a paired organ (both eyes,
both kidneys, both breasts)
- More than one childhood cancer in a set of siblings (like
sarcoma in both a brother and a sister)
Before you decide that cancer runs in your family, first
gather some information. For each case of cancer, look at:
- Who is affected? How are we related?
- What type of cancer is it? Is it rare?
- How old was this relative when they were diagnosed?
- Did this person get more than one type of cancer?
- Did they smoke?
Cancer in a close relative, like a parent or sibling (brother
or sister), is more cause for concern than cancer in a more distant
relative. Even if the cancer was from a gene mutation, the chance of it
passing on to you gets lower with more distant relatives.
It is also important to look at each side of the family
separately. Having 2 relatives with cancer is more concerning if the
people are related to each other (meaning that they are both on the
same side of the family). For example, if both relatives are your
mother's brothers it means more than if one was your father's brother
and the other was your mother's brother.
The type of cancer matters, too. More than one case of the
same rare cancer is more worrisome than cases of a more common cancer.
And having the same type of cancer in many relatives is more concerning
than if it is several different kinds of cancer. Still, in some family
cancer syndromes, a few types of cancer seem to go together. For
example, breast cancer and ovarian cancer run together in families with
hereditary breast and ovarian cancer syndrome (HBOC). Colon and
endometrial cancers tend to go together in a syndrome called hereditary
non-polyposis colorectal cancer (HNPCC).
The age of the person when the cancer was diagnosed is also
important. For example, colon cancer is rare in people under 30. Having
2 or more cases in close relatives under 30 could be a sign of a gene
syndrome. On the other hand, prostate cancer is very common in elderly
men, so if both your father and his brother were found to have prostate
cancer when they were in their 80's, it is less likely to be a gene
problem.
When many relatives have the same type of cancer it is
important to notice if the cancer could be related to smoking. For
example, lung cancer is commonly caused by smoking, so many cases of
lung cancer in a family of heavy smokers is more likely to be due to
smoking than to a gene problem.
Types of cancer
Many types of cancer are linked to a family history of that
cancer. Breast, ovarian, prostate, and colon are some of these cancers.
Some of these are discussed briefly here, but only to help explain
heredity and cancer. Please refer to the American Cancer Society
specific cancer site documents for more information about a particular
type of cancer and, its genetic components, diagnosis, and treatment.
Breast cancer
Many women are concerned that breast cancer seems to run in
their family. A woman who has a first-degree relative (such as a
mother, sister, or daughter) with breast cancer is about twice as
likely to develop breast cancer as a woman without a family history of
this cancer. Still, most cases of breast cancer, even those in close
relatives, are not part of a family cancer syndrome caused by an
inherited gene mutation.
The chance that someone has an inherited form of breast cancer
is higher the younger they are when they get the cancer and the more
relatives they have with the disease. Inherited breast cancer can be
caused by several different genes, but the most common are BRCA1 and
BRCA2. Inherited mutations in these genes cause hereditary breast and
ovarian cancer syndrome (HBOC). Along with breast and ovarian cancer,
this syndrome can also lead to male breast cancer, pancreatic cancer,
prostate cancer, as well as some others. This syndrome is more common
in women of Ashkenazi descent than it is in the general U.S.
population.
Women with a strong family history of breast cancer may choose
to undergo genetic counseling to estimate their risk for inherited
breast cancer. They then can choose to be tested to find out if they
have a breast cancer gene mutation. If a mutation is present, the woman
has a high chance (or risk) of developing breast cancer before age 40.
She may start getting mammograms at a younger age, have special breast
cancer screening tests, or take other measures to detect cancer earlier
and reduce her chance or risk of getting breast cancer.
Colon cancer
An important cause of hereditary colon cancer among adults is
a disease called familial adenomatous polyposis (FAP). People with this
disease start getting colon polyps by their teen years, and over time
may have hundreds of polyps in their colon. If left alone, at least one
of these polyps will become cancer. The gene for this syndrome is
called APC, and testing for mutations in this gene is available. If FAP
is diagnosed early in life, surgery to remove the colon can keep the
cancer from developing.
Another major inherited syndrome that increases a person's
risk for colon cancer is called hereditary non-polyposis colorectal
cancer (HNPCC). Individuals with this syndrome have a high risk of
colorectal cancer. Most of these cancers occur before age 50. HNPCC can
also cause endometrial cancer (cancer in the lining of the uterus) in
women.
Childhood cancers
Like adult cancers, most childhood cancers are not inherited.
They are caused by mutations acquired during the child's life. Some of
these may even have occurred before the child was born (while still in
the womb). A few types of childhood cancers are known to occur more
often in some families. Some of these are due to hereditary cancer
syndromes.
Retinoblastoma: This
is a childhood cancer that starts in the eye. It can be caused by an
inherited mutation in the tumor suppressor gene Rb. About 40% of
children with retinoblastoma inherited an abnormal copy of Rb from one
parent. And about 85% of children who inherit an abnormal Rb gene from
a parent develop a retinoblastoma in one or both eyes.
Even though the child inherited only 1 of the pair of
chromosomes or genes for retinoblastoma, he or she is likely to have
the disease. This is because there is no backup to stop the mutated
gene from making abnormal cells if the healthy Rb gene stops working in
even one cell. Patients with the hereditary form of retinoblastoma are
more likely to get tumors in both eyes. They also have an increased
risk of developing other types of cancer, including bone cancer.
Li-Fraumeni
syndrome: This syndrome occurs when a person inherits a
mutation in the p53 gene (a tumor suppressor gene). A normal p53 gene
stops the growth of abnormal cells. People with a p53 gene abnormality
have a higher risk of childhood sarcoma, leukemia, and brain (central
nervous system) cancers. Li-Fraumeni syndrome can also cause cancers of
the breast and adrenal glands. One study showed that 15% of Li-Fraumeni
patients who had cancer were diagnosed later with a second cancer, and
some developed a third and fourth cancer later on.
Genetic counseling and testing
People with a strong family history of cancer or multiple
types of cancer may want to find out about their genetic makeup. This
knowledge may help the person or other family members in planning
health care for the future. Since inherited mutations affect all cells
of a person's body, they can often be identified by genetic testing
which is done on blood samples. Genetic counseling and testing may be
recommended for some people with a strong family history of cancer. For
more information on genetic testing, refer to our document, Genetic Testing: What You Need
to Know.
Future directions
The Human Genome Project is an international program devoted
to determining the complete DNA sequence in humans. Although all the
genes have been listed, there is still a great deal to learn about what
proteins each gene makes. Researchers need to find out how each gene
fits into the body’s activities at the cellular level and the
effect that activity has on diseases such as cancer. The hope is that
the Human Genome Project will some day provide a single reference to
all human genetic information, including cancer genes and markers. The
impact this project will have on the future of cancer is profound. You
can read more about the Human Genome Project on the Web at www.genome.gov.
Additional resources
More information from your American Cancer
Society
We have selected some related information that may also be
helpful to you. These materials may be viewed on our Web site or
ordered from our toll-free number, 1-800-227-2345.
National organizations and Web sites*
Along with the American Cancer Society, other sources of
information and support include:
Hereditary
Cancer Center (HCC)
Toll-free number: 1-800-648-8133
Web site: http://medicine.creighton.edu/hcc
The purpose of the HCC is to evaluate and identify families at high
risk for a hereditary cancer. Once a family is identified as having a
hereditary cancer syndrome, the family is educated about the syndrome
and specific recommendations for surveillance or early detection are
provided for those family members who carry a cancer-causing gene, or
who prove to have a high risk for having a gene. Publications are also
written for family education.
National Cancer
Institute
Toll-free number: 1-800-4-CANCER (1-800-422-6237)
Web site: www.cancer.gov
Provides accurate, up-to-date information on a variety of
cancer-related topics such as finding support, financial assistance and
other resources; coping with cancer; cancer genetics, etc (click the
“Cancer Topics” tab on the home page). Also has an
Online Cancer Genetics Services Directory to identify professionals who
provide services related to cancer genetics (cancer risk assessment,
genetic counseling, genetic susceptibility testing, and others). The
direct link is www.cancer.gov/search/geneticsservices.
National Society
of Genetic Counselors (NSGC)
Telephone: 312-321-6834
Web site: www.nsgc.org
NSGC Web site offers a "Consumer Information" link with the following:
- "Making Sense of Your Genes" - a 24-page guide to genetic
counseling (may be downloaded and printed)
- Directory of genetic counselors -- may be searched by your
area
- "Five Questions to Ask Before Considering Genetic Testing"
(may be downloaded and printed)
- Guide on collecting family history -- a helpful tool in
determining possible genetic risks
- FAQs on genetic testing and genetic counselors
*Inclusion on
this list does not imply endorsement by the American Cancer Society.
No matter who you are, we can help. Contact us anytime, day or
night, for cancer-related information and support. Call us at 1-800-227-2345 or
visit www.cancer.org.
References
American Cancer Society. Cancer
Facts and Figures 2009. Atlanta, GA: American Cancer
Society, 2009.
National Institutes of Health. Chromosome Abnormalities Fact
Sheet. Accessed at National Human Genome Research Institute at
www.genome.gov/11508982 on June 9, 2009.
Taub JW. Down syndrome and leukemia — it’s
in the cards. Blood.
2004;103:2434.
Chaudru V, Chompret A, Bressac-de Paillerets B, et al.
Influence of genes, nevi, and sun sensitivity on melanoma risk in a
family sample unselected by family history and in melanoma-prone
families. J Natl Cancer
Inst. 2004; 96:785–795.
Kufe DW, Pollack RE, Weichselbaum RR, et al., eds. Cancer Medicine.
6th ed. Hamilton, Ontario: BC Decker; 2003.
Abeloff MD, Armitage JO, Niederbuber JE, Kastan MB, McKenna WG
eds. Clinical Oncology.
4nd ed. New York, NY: Churchill Livingstone; 2008.
DeVita VT, Hellman S, Rosenberg SA, eds. Cancer: Principles and Practice
of Oncology. 7th ed. Philadelphia, Pa: Lippincott Williams
& Wilkins; 2008.
Last Medical Review: 07/08/2009
Last Revised: 07/08/2009
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