Your DNA is the material in your cells that is the building blocks for your genes. Genes are the instructions that tell each cell how to grow, develop, and work. Some things your genes control are:
How fast each cell grows
How often it divides to make new cells
How long it lives
The genes in each cell are arranged in structures called chromosomes.
What are chromosomes?
Your chromosomes are the structures your genes are organized on. You can think of genes like pages in a book. The chromosome is the book the pages are in.
Each person typically has 46 chromosomes total. They are in groups of 2, so you have 23 pairs of chromosomes. One chromosome in each pair comes from your mother, and the other comes from your father.
One pair of the body's chromosomes are the sex chromosomes. The male pair has an X and a Y chromosome. In the female pair, the 2 chromosomes are both typically X.
The other 22 pairs of chromosomes are called autosomes. They determine other characteristics, such as hair color, height, and more.
How do our genes work?
Genes tell your cells what to do. They do this by making substances called proteins. Each protein has a specific job to do in your body. To make its protein correctly, each gene needs the right information. If it has this, it can make proteins that work the way they are supposed to.
Cancer starts when one or more genes in a cell change, or mutate. Different names for this include gene mutations or pathogenic variants. When this happens, the protein it makes is abnormal. Or it may not be made at all. Your body receives either no information or abnormal information. This can make cells multiply out of control and cause cancer.
Types of gene mutations or pathogenic variants
There are 2 basic types of gene mutations or pathogenic variants.
Acquired mutations. These variants, or mutations, happen on their own. "Acquired" means you get them during your lifetime. You are not born with them or inherit them.
These mutations are the most common cause of cancer. They happen when the genes in a specific cell are damaged. For example, breast cancer or colon cancer may develop if the genes in a breast or colon cell are damaged. The genes give cells the signal to divide many times without stopping as they normally would. This causes a tumor to start.
Cancer from this type of mutation is called "sporadic" cancer. The mutation simply starts in one cell somewhere in your body. It is not found in every cell in the body, and it is not passed from parent to child.
Common factors causing sporadic mutations include the following:
Ultraviolet (UV) radiation
Germline mutations. These are pathogenic variants, or mutations, that come from your parents. The mutation is in one of your mother's egg cells and/or one of your father's sperm cells. When the egg and sperm meet and form an embryo, the embryo will have the mutation.
As the embryo grows into a baby, the mutation from the original sperm or egg cell is copied into the new body's cells. This includes the sperm or egg cells. So the person can pass the mutation on to their children.
Cancer caused by germline mutations is called inherited cancer. About 5 to 20 in every 100 cancers starts from a mutation passed on by a parent.
Do mutations always cause cancer?
Not necessarily. Mutations happen often, and they can be good, bad, or neutral. It depends on where in the gene the change happens. Your body usually fixes most mutations so they do not affect you.
Having just one mutation probably will not cause cancer. Cancer is more likely when mutations build up over many years. That is why older people have cancer more often than young people do. They have lived longer, so their cells have had more time for mutations to build up.
Are there specific "cancer genes?"
Some gene variants, or mutations, are linked with cancer. These include mutations in the specific types of genes below.
Tumor suppressor genes. Genes that protect against cancer are called tumor suppressor genes. They normally limit how much a cell can grow. They do this by:
Controlling how fast cells divide to make new cells
Fixing mistakes in DNA
Controlling when a cell dies
Variants in a tumor suppressor gene can allow cells to grow out of control. These cells can eventually form a tumor.
Some tumor suppressor genes are BRCA1, BRCA2, and p53 or TP53. If a mutation in the BRCA1 or BRCA2 genes is passed down from your parents, you have a greater risk of hereditary breast, ovarian, pancreatic, and prostate cancer. Mutations in these genes also raise the risk of melanoma.
The most common tumor suppressor gene that mutates in people with cancer is p53 or TP53. This gene is missing or damaged in more than half of all cancers. Inherited p53 mutations are rare. If you have one, you have a greater risk of many different types of cancer.
Oncogenes. Mutations in certain genes can turn a healthy cell into a cancer cell. These mutations are not known to be inherited.
Two common oncogenes are:
HER2. This gene makes a protein that controls cancer growth. It is found in some cancer cells, such as some breast and ovarian cancer cells. If a breast cancer is "HER2 negative," it means the HER2 gene is not making this needed protein.
The RAS family of genes. These genes make proteins that help cells communicate with each other, grow normally, and die when they are supposed to. Mutations in these genes can turn healthy cells into cancer cells.
DNA repair genes. DNA repair genes fix mistakes that happen when your DNA is copied. DNA copying happens when cells divide normally to make new cells. Many DNA repair genes work like tumor suppressor genes do. They limit how much the cell can grow. BRCA1, BRCA2, and p53 are all DNA repair genes.
If one of your DNA repair genes has a mutation, mistakes in DNA do not get corrected. This means mutations can develop, and eventually lead to cancer. This is especially true if the mutation is in a tumor suppressor gene or an oncogene.
You can inherit a mutation in a DNA repair gene, or it can happen on its own over your lifetime. Lynch syndrome is caused by an inherited DNA repair mutation. Mutations in BRCA1, BRCA2, and p53 are inherited too.
Learn more about hereditary cancer-related syndromes.
What is known about genes and cancer?
Researchers have learned a lot about how genes are involved in cancer. But many cancers are not linked with any specific gene. When cancer develops, several gene mutations are probably involved, not just one.
Also, gene mutations are not the only cause of cancer. Your everyday environment can also affect how genes and gene mutations work. Together, your genes and your environment can determine if you develop cancer.
Researchers continue to study genes and cancer. What they have learned so far has helped improve cancer care. It has given doctors new ways to find cancer early, lower your risk, treat cancer with new treatments such as targeted therapy, and live longer.
More studies about genes and cancer may help researchers learn how to do the following in the future:
Predict a person's individual risk of cancer
Find cancer more easily when it is smaller
Treat different types of cancer better
Questions to ask the health care team
Is my cancer caused by a genetic mutation?
Did one of my parents pass on the genetic mutation that caused my cancer? Is my cancer part of an inherited syndrome?
Could I pass a genetic mutation that causes cancer to my children?
Was there anything in my environment that could have caused my cancer?
Does knowing about my genes help us choose the best cancer treatment?
Should other people in my family have genetic testing? Who can we talk to about this?
Genetic Testing for Cancer Risk
What Is Personalized Cancer Medicine?
Introduction to Cancer Research
Expert Perspectives about Genetics and Cancer
National Cancer Institute: The Genetics of Cancer