Most basal cell and squamous cell skin cancers are caused by unprotected exposure of the skin to ultraviolet (UV) rays. This radiation comes from sunlight, as well as from man-made sources such as tanning beds.
Repeated and unprotected sun exposure over many years increases a person's risk of skin cancer. Most skin cancers are probably caused by exposures that happened many years earlier. The pattern of exposure may also be important. For example, frequent sunburns in childhood may increase the risk for basal cell cancer many years or even decades later.
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. However, DNA affects more than just how we look. Some genes contain instructions for controlling when our cells grow, divide, and die.
UV radiation (from sunlight or tanning lamps) can damage DNA. Sometimes this damage affects certain genes that control how and when cells grow and divide. Usually the cells can repair the damage, but in some cases this results in abnormal DNA, which may be the first step on the path to cancer.
Researchers don't yet know all of the DNA changes that result in skin cancer, but they have found that many skin cancers have changes in tumor suppressor genes. These genes normally function to help keep cells from growing out of control.
The gene most often found to be altered in squamous cell cancers is called p53. This gene normally causes damaged cells to die. When this gene is altered, these abnormal cells may live longer and perhaps go on to become cancerous.
A gene commonly found to be mutated in basal cell cancers is the "patched" (PTCH) gene. This tumor suppressor gene normally helps keep cell growth in check, so changes in this gene can allow cells to grow out of control. People who have basal cell nevus syndrome, which is often inherited from a parent and results in many basal cell cancers, have an altered PTCH gene in all the cells of their body.
These are not the only gene changes that may play a role in the development of skin cancer. There are likely to be many others as well.
People with xeroderma pigmentosum (XP) have a high risk for skin cancer. XP is a rare, inherited condition resulting from a defect in an enzyme that repairs damage to DNA. Because people with XP are less able to repair DNA damage caused by sunlight, they develop huge numbers of cancers on sun-exposed areas of their skin.
The link between squamous cell skin cancer and human papilloma virus (HPV) infection also involves DNA and genes. These viruses contain genes that instruct infected cells to make certain proteins that affect the growth-regulating proteins of normal skin cells. This can cause skin cells to grow too much and to not die when they're supposed to.
Scientists are studying other links between DNA changes and skin cancer. In the future, better understanding of how damaged DNA leads to skin cancer might be used to design treatments to overcome or repair that damage.
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