A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs.
But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have any known risk factors. Even if a person with melanoma has a risk factor, it is often very hard to know how much that risk factor may have contributed to the cancer.
Scientists have found several risk factors that may make you more likely to develop melanoma.
Ultraviolet (UV) light exposure
Ultraviolet (UV) radiation is a major risk factor for most melanomas. Sunlight is the main source of UV radiation, which can damage the genes in your skin cells. Tanning lamps and beds are also sources of UV radiation. People with high levels of exposure to light from these sources are at greater risk for skin cancer, including melanoma.
Ultraviolet radiation is divided into 3 wavelength ranges:
- UVA rays cause cells to age and can cause some damage to cells' DNA. They are linked to long-term skin damage such as wrinkles, but are also thought to play a role in some skin cancers.
- UVB rays can cause direct damage to the DNA, and are the main rays that cause sunburns. They are also thought to cause most skin cancers.
- UVC rays don't get through our atmosphere and therefore are not present in sunlight. They are not normally a cause of skin cancer.
While UVA and UVB rays make up only a very small portion of the sun's wavelengths, they are the main cause of the damaging effects of the sun on the skin. UV radiation damages the DNA of skin cells. Skin cancers begin when this damage affects the DNA of genes that control skin cell growth. Both UVA and UVB rays damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on what is known today, there are no safe UV rays.
The amount of UV exposure depends on the strength of the rays, the length of time the skin is exposed, and whether the skin is protected with clothing or sunscreen.
The nature of the UV exposure may play a role in melanoma development. Many studies have linked the development of melanoma on the trunk (chest and back) and legs to frequent sunburns (especially in childhood). The fact that these areas are not constantly exposed to UV light may also be important. Some experts think that melanomas in these areas are different from those on the face and neck, where the sun exposure is more constant. And different from either of these are melanomas that develop on the palms of the hands, soles of the feet, under the nails, or on internal surfaces such as the mouth and vagina, where there has been little or no sun exposure.
For information on how to protect yourself and your family from UV exposure, see the section called "Can melanoma be prevented?"
Moles
A nevus (the medical name for a mole) is a benign (non-cancerous) melanocytic tumor. Moles are not usually present at birth but begin to appear in children and young adults. Most moles will never cause any problems, but a person who has many moles is more likely to develop melanoma.
Dysplastic nevi: Dysplastic nevi (nevi is the plural of nevus), also called atypical nevi, often look a little like normal moles but also look a little like melanoma. They are often larger than other moles and have an abnormal shape or color. (See the section called "Can melanoma be found early?" for descriptions of how moles and melanomas look.) They can appear on skin that is exposed to the sun as well as skin that is usually covered, such as on the buttocks and scalp.
A small number of dysplastic nevi may develop into melanomas. But most dysplastic nevi never become cancerous, and many melanomas seem to arise without a pre-existing dysplastic nevus.
Lifetime melanoma risk may be higher than 10% for those with many dysplastic nevi (sometimes referred to as dysplastic nevus syndrome). Dysplastic nevi often run in families. Someone with many dysplastic nevi and with several close relatives who have had melanoma has a 50% or greater lifetime risk of developing melanoma.
People with this condition should have very thorough, regular skin exams by a dermatologist (a doctor who specializes in skin problems). In some cases, full body photographs are taken to help the doctor recognize which moles are changing and growing. Many doctors recommend that patients be taught to do monthly skin self-exams and be counseled about sun protection.
Congenital melanocytic nevi: Moles present at birth are called congenital melanocytic nevi. The lifetime risk of getting melanoma for people with congenital melanocytic nevi has been estimated to be between 0 and 10%, depending on the size of the nevus. People with very large congenital nevi have a greater risk, while the risk is smaller for those with small nevi.
Congenital nevi are sometimes removed by surgery so that they do not have a chance to become cancerous. Whether or not doctors advise removing a congenital nevus depends on several factors including its size, location, and color. Many doctors recommend that congenital nevi that are not removed should be examined at regular intervals by a dermatologist and that the patient should be taught how to do monthly skin self-exams.
Again, the chance of any single mole turning into cancer is very low. However, anyone with lots of irregular or large moles has an increased risk for melanoma.
Fair skin, freckling, and light hair
The risk of melanoma is more than 10 times higher for whites than for African Americans. Whites with red or blond hair, blue or green eyes, or fair skin that freckles or burns easily are at increased risk.
Family history of melanoma
Your risk of melanoma is greater if 1 or more first-degree relatives (mother, father, brother, sister, child) has had melanoma. Around 10% of all people with melanoma have a family history of the disease.
The increased risk might be due to a shared family lifestyle of frequent sun exposure, a family tendency to have fair skin, or a combination of both factors. It may also be due to inherited gene changes (mutations) in a family. Gene mutations have been found in anywhere from about 10% to 40% of families with a high rate of melanoma. Most experts do not recommend genetic testing in these families at this time. Rather, they advise that people with a strong family history of melanoma do the following:
- Have regular skin exams by a dermatologist
- Thoroughly examine your skin once a month
- Be particularly careful about sun protection and avoid artificial UV rays (such as those from tanning booths)
Personal history of melanoma
A person who has already had melanoma has an increased risk of getting melanoma again. About 5% to 10% of people with melanoma will develop a second one at some point.
Immune suppression
People who have been treated with medicines that severely suppress the immune system, such as organ transplant patients, have an increased risk of melanoma.
Age
Although melanoma is more likely to occur in older people, this is a cancer that is also found in younger people. In fact, melanoma is one of the most common cancers in people younger than 30. Melanoma that runs in families may occur at a younger age.
Gender
In the United States, men have a higher rate of melanoma than women.
Xeroderma pigmentosum
Xeroderma pigmentosum (XP) is a rare, inherited condition resulting from a defect in an enzyme that normally repairs damage to DNA. People with XP have a high risk for developing melanoma and other skin cancers at a young age. Because people with XP are less able to repair DNA damage caused by sunlight, they can develop many cancers on sun-exposed areas of their skin.
No comments:
Post a Comment