Cancer Genetics 101

Our bodies are made up of billions of cells. In our cells there are structures called chromosomes that are made up of a long string of letters called our DNA. Our DNA is divided up into about 20,000 genes.  Most of our genes come in pairs: one copy from our mother, and one copy from our father.  Our genes provide the instructions to build proteins for everything we need to grow and function, from determining the color of our hair to how sticky our ear wax is.

One important function that some genes perform is regulating how quickly cells grow and divide. Cancer starts when cells begin to grow and divide out of control.

Most of the genes that are related to inherited cancer risk are ones that normally protect us from getting cancer.  These are sometimes referred to as “tumor suppressor” genes.  The job of these genes is to repair damage to our DNA and to help keep cells from growing out of control. As cells in the body are dividing to make more cells, they have to copy the long string of letters that make up our DNA. As that copying process is happening, there are bound to be spelling errors that happen, which we call genetic damage. Genetic damage can be caused by random chance, or by exposure to things in the environment like UV rays from the sun, cigarette smoke, toxins, or certain types of viruses.

One gene that is commonly thought of when considering inherited cancer risk genes is the BRCA1 gene.  Breaking down the name of this gene: BR stands for BReast, the CA for CAncer, and the number 1 is because this was the first gene discovered that was known to be associated with breast cancer in families.  This is a gene that we all carry, both males and females, and each of us inherit one copy of the BRCA1 gene from our mother and one from our father.  

Individuals who inherit a non-working copy of the BRCA1 gene from either parent have a higher chance to develop breast, ovarian, prostate, and pancreatic cancers. When the BRCA1 genes are working properly, they result in proteins that work in a complex with other proteins to repair damage to your DNA.  Imagine that this is like a spell-check machine, at work to correct any typos in the DNA string (genetic damage).   Sometimes genetic damage can occur to one copy of an individual’s BRCA1 genes. In most cases, this does not result in cancer, because most people have two working copies of the BRCA1 gene. If something happens to one copy of the gene, then most people have a second copy of the gene as a spare, or a backup, and you only need one copy of that gene to keep the spell check machinery working. But if something else happens down the line to damage your other copy of the BRCA1 gene, then the spell check machinery would break down and genetic damage would build up. Genetic damage building up is what can cause a cell to grow out of control, which is what can lead to cancer. This is how cancer can start in anyone (sporadic cancer).

Cancer can run in a family, or be inherited, when a change (or mutation) is passed on in a gene such as BRCA1 through the sperm or the egg. Every cell in our bodies copies over the genetic information that is passed on from the sperm and the egg.  In individuals with an inherited risk for cancer, every cell in their body only has one working copy of that gene. They are essentially one step closer to cancer because they do not have that backup, or spare copy of the BRCA1 gene. If something happens to their one working copy of BRCA1, their spell check machinery essentially breaks down. Because of this, people who inherit mutations in these genes have a higher lifetime risk to get related cancers, have a higher risk to get cancer at younger ages, and (depending on the gene) have increased risks to get cancer more than one time in their life.

We have known about and been testing people for mutations in the BRCA1 gene since the 1990’s, but research through the years has shown that a number of other genes have a link to various types of hereditary cancer. Genetic counselors are specialists who can help answer questions and assess personal and family histories to determine if someone is at a high risk for a hereditary cancer syndrome.

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