All Cancer is Genetic But Few Cancers Are Inherited

Richard Whitten


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All cancers have genetic abnormalities. This means the cancer cell’s DNA or genes (which reside in the chromosomes) show alterations. In some cancers it seems to take only a single change to cause the cancerous growth.

For example, one type of leukemia (chronic myelogenous leukemia, or CML), shows a characteristic break between two separate chromosomes with abnormal joining of part of one (chromosome 22) to part of the other (chromosome 9) creating a new abnormal fused chromosome (the famous Philadelphia chromosome).

This break and reconnection brings together, or fuses, two normally separate genes that now behave abnormally, creating uncontrolled cancerous cell growth.

What does this mean, exactly?
All cancers have genetic abnormalities in the cancer cells themselves, but the person who has the cancer does not show these abnormalities in any other cells of their body including their germ cells (eggs and sperm), so they are not passed on to future generations or inherited.

What about the “breast cancer gene”?
There are uncommon hereditary cancers, however. Abnormal genes that were present in the parent’s eggs or sperm can mean an individual inherits an increased risk to develop cancer.

An example is the famous BRCA-1 mutation that increases the risk of breast, ovarian and other cancers in those who inherit a mutated BRCA-1 gene. All cells have 2 copies of every gene and if one inherits mutations in both copies of an important gene like BRCA-1, then the embryo usually does not survive and is spontaneously aborted early in pregnancy, often before the mother knows she is pregnant.

If one inherits a mutation in only one of the copies of the gene then the embryo lives, but has an increased risk of problems such as developing breast cancer in the case of BRCA-1. Most breast cancers do not occur in patients with this hereditary risk, but if you do inherit a mutation in BRCA-1, then your risk is many times higher that you will develop breast or ovarian cancer in your lifetime. That is, most breast cancers arise in patients without a hereditary BRCA-1 mutation or other family history of early or frequent breast cancer.

Another example is an inherited mutation in one of the copies of a DNA repair gene (one that fixes mistakes that invariably occur during copying of DNA to make a new cell) that is inherited and leads to an increased lifetime risk for colon cancer called the Lynch syndrome. Like the BRCA-1 situation, this inherited risk accounts for only a small fraction of all colon cancers (15%), but if you have this mutation, your lifetime risk is much higher than someone who did not inherit the mutation.

What do I do?
If several close family members have developed these cancers at unusually young ages (that is you have a family history of these cancers), then you may carry one of these mutations. Laboratory tests are available to look for the BRCA-1 and Lynch syndrome mutations and several others that are known to lead to an increased hereditary risk for cancers. Talk to your doctor about the appropriateness of genetic testing and counseling for your individual situation.

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