Kaposi's sarcoma - Causes of Kaposi's sarcoma

Kaposi's sarcoma is caused by a virus called the human herpesvirus 8 (HHV-8), also known as the Kaposi's sarcoma-associated herpesvirus (KSHV).

It's thought this virus can alter the genetic instructions that control cell growth. This means some cells reproduce uncontrollably and form lumps of tissue known as tumours.

However, HHV-8 is a relatively common virus and not everyone who has it will develop Kaposi's sarcoma. The virus only seems to cause the condition in some people with:

• a weakened immune system – this is thought to be the reason why people develop HIV-related Kaposi's sarcoma and transplant-related Kaposi's sarcoma
• an inherited (genetic) vulnerability to HHV-8 – this is thought to be the reason why people develop either classic Kaposi's sarcoma or "endemic" African Kaposi's sarcoma 

Read more about the types of Kaposi's sarcoma.

How the virus is spread

Although HHV-8 was identified almost 20 years ago, there's still no firm evidence about how it is spread. Some theories for how the virus spreads include:

• sexual transmission, particularly between men who have unprotected anal sex with other men
• saliva, possibly including kissing
• sharing needles and syringes used for injecting drugs
• from mother to baby during birth

However, more research is needed to determine exactly how the virus is spread.