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. It can be because
family members have certain risk factors in common, such as smoking,
which can cause many types of cancer. It can also be due in part to some other factors, like obesity, that tend to run in families and influence cancer risk.
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 –
resulting directly from gene defects (called mutations) inherited from a parent. This document focuses on those cancers.
An abnormal change in a gene is called a mutation. The 2 types of mutations are inherited and acquired (somatic).
- Inherited gene mutations are passed from parent to child through the egg or sperm. These mutations are in every cell in the body.
- Acquired (somatic) mutations are not present in the egg or sperm. These mutations are acquired at some point in the person's life, and are more common than inherited mutations. 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 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.
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, or 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).
Certain things make it more likely that an abnormal gene is causing cancers in a family, such as
- Many cases of an uncommon or 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 pair of organs (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 or have other known risk factors?
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