A risk factor is anything that may increase your chance of having a disease. For instance, risk factors for a certain type of cancer might include smoking, diet, family history, or many other things. Most of the time, the exact cause of someone's cancer isn't known. But risk factors can make it more likely for a person to have cancer.

Things you should know about risk factors for cancer:

• Risk factors can increase a person's risk, but they do not always cause the disease.
• Some people with risk factors never develop cancer. Other people with cancer have few or no risk factors.
• Some risk factors are very well known. But there's ongoing research about risk factors for many types of cancer.

Some risk factors, such as family history, may not be in your control. But others may be things you can change. Knowing the risk factors can help you make choices that might help lower your risk. For instance, if an unhealthy diet is a risk factor, you may choose to eat healthy foods. If excess weight is a risk factor, you may decide to try to lose weight.

Anyone can get Kaposi sarcoma (KS). But there are some factors that can increase your risk, such as:

• Gender. Men have a higher risk for KS than women.
• Ethnic background. People of Mediterranean, Italian, or Eastern European Jewish descent have a higher risk for a rare type of KS called classic Kaposi sarcoma. People living in certain parts of Africa have a higher risk for some types of KS.
• Infection with human herpesvirus-8 (HHV-8). This virus is also known as Kaposi sarcoma-associated herpesvirus (KSHV). It seems that a person must have this virus in order for KS to develop. But most people infected with this virus don't develop KS. It can spread through saliva, semen, vaginal fluid, and from mother to child.
• Having a weakened immune system. People with a weakened immune system are at increased risk for KS. This includes people infected with HIV, the virus that causes AIDS. Or people who have had an organ transplant. This is likely because their weakened immune system is not able to keep an HHV-8 infection under control.
• Sexual activity. Men who have sex with men are at higher risk for KS. This is probably because they're more likely to be infected with both HHV-8 and HIV.

Talk with your doctor about your risk factors for KS and what you can do about them. Some risk factors, such as your gender and ethnicity, are not under your control. But some are. For instance, taking steps to avoid the risk of HIV infection might lower your risk for KS.

If you are infected with HIV, talk with your doctor about what you can do to help keep your immune system strong. Also talk about any symptoms you should watch for that might be early signs of KS.