Do we know what causes melanoma skin cancer?
Although researchers have found some things that can raise a person’s risk of melanoma (see “What are the risk factors for melanoma skin cancer?”), it’s not yet clear exactly how these factors cause melanoma.
For example, while most moles never turn into a melanoma, some do. Researchers have found some gene changes inside mole cells that may cause them to become melanoma cells. But it is still not known exactly why some moles become cancerous or why having many moles or atypical (dysplastic) moles increases your risk of developing melanoma.
Researchers have learned a great deal in recent years about how certain changes in DNA can make normal cells become cancerous. DNA is the chemical in each of our cells that makes up our genes – the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. But DNA affects more than just how we look.
Some genes control when our cells grow, divide into new cells, and die. Certain genes that help cells grow, divide, and stay alive are called oncogenes. Genes that keep cell growth in check or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes. Changes in several different genes are usually needed for a cell to become cancerous.
Ultraviolet (UV) rays are clearly a major cause of many melanomas. UV rays can damage the DNA in skin cells. Sometimes this damage affects certain genes that control how skin cells grow and divide. If these genes no longer work properly, the affected cells may form a cancer.
Most UV rays come from sunlight, but some can come from man-made sources such as tanning beds. Usually it’s not clear exactly when UV exposure causes DNA damage that might eventually lead to cancer. Some of the damage may take place in the few years before the start of the cancer. But much of it may be from exposures that happened many years earlier. Children and young adults often get a lot of intense sun exposure that might not result in cancer until many years or even decades later.
Most of the gene changes commonly seen in melanoma cells are not inherited. They are more likely the result of damage caused by sunlight. In some people, such as those with xeroderma pigmentosum (XP), the skin cells are not as able to repair damaged DNA. These people are more likely to develop melanoma.
Some melanomas occur in parts of the body that are rarely exposed to sunlight. These melanomas often have different gene changes than those in melanomas that develop in sun-exposed areas.
When melanomas run in families, gene mutations that greatly increase the risk of melanoma are often passed from one generation to the next. Familial (inherited)
melanomas most often have changes in tumor suppressor genes such as CDKN2A (also known as p16) and CDK4 that prevent them from doing their normal job of controlling cell growth. Scientists reason that this could eventually lead to cancer.
Many other gene changes have been found in melanoma cells as well. Some of these have proven to be good targets for drugs to help treat this disease. For example, about half of all melanomas have a change (mutation) in the BRAF oncogene that helps drive their growth. This change is not inherited. It seems to occur during the development of the melanoma. Several drugs that specifically target cells with this gene change are now used to treat these melanomas (see the section “Targeted therapy for melanoma skin cancer”).
Can melanoma skin cancer be prevented?
Not all melanomas can be prevented, but there are things you can do that could reduce your risk of getting melanoma and other skin cancers.
Limit your exposure to ultraviolet (UV) rays
The most important way to lower your risk of melanoma is to protect yourself from exposure to UV rays. Practice sun safety when you are outdoors.
Seek shade
Simply staying in the shade is one of the best ways to limit your UV exposure.
“Slip! Slop! Slap!®… and Wrap”
If you are going to be in the sun, this catchphrase can help you remember some of the key steps you can take to protect yourself from UV rays:
• Slip on a shirt.
• Slop on sunscreen.
• Slap on a hat.
• Wrap on sunglasses to protect the eyes and sensitive skin around them.
Avoid tanning beds and sunlamps
Many people believe the UV rays of tanning beds are harmless. This is not true. Tanning lamps give out UV rays, which can cause long-term skin damage and can contribute to skin cancer. Tanning bed use has been linked with an increased risk of melanoma, especially if it is started before a person is 30. Most dermatologists (skin doctors) and health organizations recommend not using tanning beds and sun lamps.
Protect children from the sun
Children need special attention, since they tend to spend more time outdoors and can burn more easily. Parents and other caregivers should protect children from excess sun exposure by using the steps above. Children need to be taught about the dangers of too much sun exposure as they become more independent.
To learn more about sun safety
For more information on how to protect yourself and your family from UV exposure, see our document Skin Cancer: Prevention and Early Detection.
Watch for abnormal moles
Checking your skin regularly may help you spot any new or abnormal moles or other growths and show them to your doctor before they even have a chance to turn into skin cancer.
Certain types of moles are more likely to develop into melanoma (see the section “What are the risk factors for melanoma skin cancer?”). If you have moles, depending on how they look, your doctor may want to watch them closely with regular exams or may remove some of them if they have certain features that suggest they might change into a melanoma.
Routine removal of many moles is not usually recommended as a way to prevent melanoma. Some melanomas may develop from moles, but most do not. If you have many moles, getting careful, routine exams by a dermatologist, along with doing monthly skin self-exams, might be recommended.
If you find a new, unusual, or changing mole, you should have it checked by a doctor experienced in recognizing skin cancers. See the section “Signs and symptoms of melanoma skin cancer” for descriptions of what to look for.
Genetic counseling and testing for people at high risk
Gene mutations (changes) that increase melanoma risk can be passed down through families, but they account for only a small portion of melanomas. You might have inherited a gene mutation that increases your risk of melanoma if any of the following apply:
• Several members of one side of your family have had melanoma
• A family member has had more than one melanoma
• A family member has had both melanoma and pancreatic cancer
• You have had more than one melanoma
Some families with high rates of melanoma have mutations in genes such as CDKN2A (also known as p16). Tests for these gene changes are now available, although they are not widely recommended by doctors at this time. People interested in learning whether they carry gene changes linked to melanoma may want to think about taking part in genetic research that will advance progress in this field.
It is very important to meet with a genetic counselor before deciding if you should have testing. The counselor can describe the tests to you and explain what the results may or may not tell you about your risk. Genetic testing is not perfect, and in some cases the tests may not provide solid answers. To learn more about genetic testing in general, see Genetic Testing: What You Need to Know.
At this time, because it’s not clear how useful the test results might be, most melanoma experts don’t recommend genetic testing for people with a personal or family history of melanoma. Still, some people may choose to get tested. In any event, people with a family history of melanoma should ask their doctor about getting regular skin exams, learning to do skin self-exams, and being particularly careful about sun safety.
