Kaposi's sarcoma is a rare type of cancer caused by a virus.
It affects the skin and mouth, and sometimes the internal organs.
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Kaposi's sarcoma is mostly seen in people with an advanced HIV infection.
It can also affect people with a weakened immune system for another reason, such as after having an organ transplant.
People with a genetic vulnerability to the virus that causes Kaposi's sarcoma – the human herpesvirus 8 (HHV-8) – are also at risk.
The main symptom of Kaposi's sarcoma is skin lesions.
These are small, painless, discoloured patches on the skin or inside the mouth.
Lesions are usually red or purple and look like bruises. Over time, they may grow into lumps (nodules) and merge into each other.
Sometimes internal organs, such as the lymph nodes, lungs and digestive system, are affected.
This can cause:
How quickly the symptoms progress depends on the type of Kaposi's sarcoma. Without treatment, most types get worse quickly in a matter of weeks or months. Some types progress very slowly over many years.
See your GP if:
If you have HIV, you can also contact your local HIV clinic if you have any concerns.
If your GP thinks you may have Kaposi's sarcoma, they'll refer you for further tests to confirm the diagnosis.
You'll need to have an endoscopy if it's thought you have Kaposi's sarcoma in your digestive system.
A long, thin, flexible tube with a light and camera at one end (an endoscope) is passed down your throat so the inside of your body can be examined.
Sometimes a CT scan may also be used to check whether your lymph nodes or other parts of your body are affected.
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).
The virus is thought to be spread during sex, through blood or saliva, or from a mother to her baby during birth.
HHV-8 is a relatively common virus, and most people who have it won't develop Kaposi's sarcoma.
It only seems to cause cancer in some people with a weakened immune system and those who have a genetic vulnerability to the virus.
A weakened immune system allows the HHV-8 virus to multiply to high levels in the blood, increasing the chance of it causing Kaposi's sarcoma.
The virus appears to alter the genetic instructions that control cell growth. It affects the endothelial cells, which line the inside surface of blood vessels and lymphatic vessels.
The endothelial cells reproduce uncontrollably and form lumps of tissue known as tumours.
There are four main types of Kaposi's sarcoma, and each is treated in a different way.
Kaposi's sarcoma is one of the main types of cancer to affect people with HIV. It can progress very quickly if it isn't treated.
It can usually be treated very effectively by taking HIV medication known as combination antiretroviral therapy (cART).
This prevents HIV multiplying and allows the immune system to recover. The immune system can then reduce the levels of HHV-8 in the body.
Some people may also need other treatments, such as chemotherapy or interferon (a type of biological therapy).
Classic Kaposi's sarcoma is very rare, and mainly affects the skin on the lower legs and feet.
Unlike other types of Kaposi's sarcoma, the symptoms of classic Kaposi's sarcoma progress very slowly over many years.
It's thought people with classic Kaposi's sarcoma are born with a genetic vulnerability to the HHV-8 virus. It's most common in older men of Mediterranean or Jewish origin.
The condition doesn't affect life expectancy, so immediate treatment isn't usually needed. You'll be closely monitored, and treatment may be recommended if the affected areas of skin are large and visible.
Radiotherapy can be used to treat the affected areas of skin. Cryotherapy (freezing) or minor surgery may also be used to remove the skin lesions.
Transplant Kaposi's sarcoma is a rare complication of an organ transplant.
After an organ transplant, you're given medication called immunosuppressants to prevent your body rejecting the donated organ.
This suppresses or weakens your immune system. But it can allow a previous HHV-8 infection to reactivate and the virus to start multiplying again.
Transplant Kaposi's sarcoma can be aggressive and needs to be treated quickly. Reducing or changing immunosuppressants can help. If this is unsuccessful, radiotherapy or chemotherapy may be needed.
Endemic or African Kaposi's sarcoma is common in parts of Africa where the HHV-8 infection is widespread.
In many cases it's caused by an undiagnosed HIV infection, and HIV medication is the most effective treatment.
In cases that aren't caused by an HIV infection, chemotherapy or radiotherapy may be needed.
With the right treatment, Kaposi's sarcoma can usually be controlled for many years. Deaths from the condition are uncommon in the UK.
The lesions will often shrink and fade with treatment, but may not disappear completely.
It may not be possible to cure Kaposi's sarcoma completely, and there's always a chance it could come back in the future.
Contact your GP, local HIV clinic or hospital specialist as soon as possible if you've had Kaposi's sarcoma in the past and think it may have returned.
Most cases of HIV-related Kaposi's sarcoma can be successfully treated with a combination of anti-retroviral therapy and chemotherapy. Once the immune system has fully recovered, it's unlikely to relapse.