What are the risk factors for Merkel cell carcinoma?
A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking and too much sun exposure, can be changed. Others, like a person’s age or family history, can’t be changed.
But having a risk factor, or even many risk factors, does not mean that you will get the disease. And some people who get the disease may have few or no known risk factors.
There are a few known risk factors for Merkel cell carcinomas (MCCs).
Infection with Merkel cell polyomavirus (MCV)
Evidence of the Merkel cell polyomavirus can be found in the cells of nearly all Merkel cell carcinomas. MCV is a common virus. Most people are infected with MCV at some point (often before the age of 20), but the infection is not known to cause symptoms, and it rarely leads to MCC. Because of this, there are no recommended screening tests for MCV infection.
MCV was first discovered in 2008, so there’s still a lot that scientists don’t know about this virus. For example, it’s not clear how people are infected with MCV, exactly how it might cause MCC, and if infection with MCV is required before MCC can develop.
Ultraviolet (UV) light exposure
Exposure to ultraviolet (UV) rays is thought to be a major risk factor for most skin cancers, including MCC. UV rays damage the DNA inside skin cells. This can result in skin cancers if this damage affects the DNA of genes that control skin cell growth. There are 3 main types of UV rays:
- UVA rays cause skin cells to age and can damage their DNA. These rays are mainly linked to long-term skin damage such as wrinkles, but are also thought to play a role in some skin cancers.
- UVB rays can directly damage skin cells’ DNA, and are the main cause of sunburns. They are also thought to cause most skin cancers.
- UVC rays don’t get through our atmosphere and are not present in sunlight. They do not normally cause skin cancer.
Both UVA and UVB rays can damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on what’s known today, there are no safe UV rays.
From the sun: Sunlight is the main source of UV rays. Most MCCs start in areas of the body often exposed to the sun, such as the face, neck, and arms. People who get a lot of sun exposure are at greater risk for MCC.
While UVA and UVB rays make up only a very small portion of the sun’s rays, they are the main cause of the damaging effects of the sun on the skin.
From tanning beds: Tanning beds are another source of UV rays for some people. MCC is an uncommon cancer, and no studies have looked for a link between MCC and tanning bed use. But it stands to reason that more exposure to UV rays might increase the risk.
From psoriasis treatments: Some patients with psoriasis (a long-lasting inflammatory skin disease) are given medicines called psoralens along with UV light, which is known as PUVA treatments. This can increase the risk of developing MCC.
Having light-colored skin
The risk of MCC is much higher for whites than for African Americans or Hispanics. This is likely due to the protective effect of darker skin against the damaging effects of UV rays.
The risk of MCC rises as people get older. In fact, this cancer is very rare before the age of 50. The increased risk is probably related to skin damage caused by sun exposure over time and to the fact that people’s immune systems tend to become weaker as they get older.
Men are more likely than women to develop MCC. This might be because they tend to get more sun exposure.
Weakened immune system
The immune system defends the body against germs such as viruses. It also seems to help the body fight some cancers of the skin and other organs. People with weakened immune systems (from certain medical treatments or diseases) are more likely to develop some types of skin cancer, including MCC.
For example, people who get organ transplants are usually given medicines that weaken their immune system to prevent their body from rejecting the new organ. This increases their risk of developing MCC. People with autoimmune diseases (such as lupus) sometimes take medicines that suppress the immune system, which might increase their risk.
People infected with HIV, the virus that causes AIDS, often have weakened immune systems and are also at increased risk for MCC.
People with some types of blood cancers, such as chronic lymphocytic leukemia (CLL) or certain lymphomas, also tend to have weakened immune systems. This can be from the cancer itself or from its treatment. People with these cancers are more likely to get MCC.
MCCs in people with weakened immune systems tend to grow faster and are more likely to be life-threatening.
Last Medical Review: 12/31/2013
Last Revised: 12/31/2013