All forms of Kaposi sarcoma (KS) are caused by a type of herpesvirus, Kaposi sarcoma herpesvirus (KSHV).
Most people with KSHV do not develop Kaposi sarcoma unless their immune system is suppressed.
The incidence of Kaposi sarcoma increased 20-fold during the spread of HIV in the early 1990s and this type of cancer is still seen most often in people with late-stage HIV, as well as in people taking immunosuppressant medications.
What is it?
Kaposi sarcoma is a type of cancer caused by a virus.
Kaposi sarcoma is a multicentric vascular tumor, meaning that it involves blood vessels and affects soft tissue in multiple areas of the body.
It originates in the endothelial cells that line blood vessels and lymphatic vessels, causing these to grow at a faster rate and to survive for longer than normal.
There are four main types of Kaposi sarcoma:
- Classic KS: This occurs mainly in older adults of Mediterranean, Eastern European, and Middle Eastern descent. It is more common in males than females.
- Epidemic KS: This is the most common form of KS.
- Endemic KS: Also known as African Kaposi sarcoma, this form is relatively common in equatorial Africa and can affect children and adults independently of HIV transmission.
- Iatrogenic KS: This is also known as immunosuppressive treatment-related Kaposi sarcoma, immunosuppressive Kaposi sarcoma, or transplant-related Kaposi sarcoma.
The appearance of Kaposi sarcoma lesions has historically triggered a diagnosis of late-stage HIV.
There have been reports more recently, however, of Kaposi sarcoma occurring in people whose HIV is being well managed with antiretroviral medications, and whose viral load is undetectable.
This has led some physicians to question whether Kaposi sarcoma should still be considered a diagnostic factor in stage 3 HIV.
Typical Kaposi sarcoma lesions
Image credit: Anatomy & Physiology, Connexions Web site, 2013 - Kaposi sarcoma lesions
Kaposi sarcoma lesions before Interferon treatment
Image credit: National Cancer Institute, 1987 - Kaposi sarcoma before
Kaposi sarcoma lesions after Interferon treatment
Image credit: Image credit: McLeod, 2008 - Kaposi sarcoma after
Kaposi lesions under a microscope
Image credit: CFCF, 2009 - Kaposi sarcoma
The cause of Kaposi sarcoma was identified recently due to the association between the lesions and HIV.
Although some physicians had long suspected that an infectious agent was the cause of Kaposi sarcoma, it was only in the wake of the HIV epidemic that this theory was seriously explored.
In 1994, Chang and Moore investigated genetic material from Kaposi tumors and discovered a new virus, the Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8).
Most of us are infected with at least one type of herpesvirus, but a healthy immune system can usually keep these from causing harm.
Almost all Kaposi sarcoma lesions contain viral DNA from HHV8.
While the growth of Kaposi sarcoma almost certainly requires HHV8, exactly how the virus causes the tumor is still under investigation.
Human herpesvirus 8 has several modes of transmission. It can be spread both sexually and non-sexually, including through organ transplantation and breastfeeding.
HHV8 infection appears to be more easily spread through certain types of sexual activity, including oral-anal contact, oral-genital contact, and deep kissing, due to the presence of KSHV in saliva. Rates of HHV8 infection are much higher in men who have sex with men when compared to the general population.
As rates of HIV are also typically higher in this group, and the condition can compromise immunity, the incidence of Kaposi sarcoma is also higher in men with HIV.
People with weaker immune systems are at risk of Kaposi sarcoma, including individuals who are taking medication to suppress the immune system after an organ transplant and seniors whose immunity has declined.
Endemic Kaposi sarcoma occurs in people living in Equatorial Africa. Infection with HHV8 is much more common in Africa than elsewhere in the world, and the higher risk of malaria, other chronic infections and malnutrition may also compromise immunity.
Due to a high rate of HIV in Africa, epidemic Kaposi sarcoma has taken over from the endemic form as the most common type.
Kaposi sarcoma lesions are distinctive in appearance.
People with Kaposi sarcoma do not always present signs or symptoms of the cancer. In many people, however, asymptomatic skin lesions indicate the disease.
Kaposi sarcoma often presents as marks on the skin with the following characteristics:
- brown, purple, pink, or red blemishes called macules
- the tendency to merge into plaques and nodules that range from blue-violet to black in appearance
- occasional swelling and outward growth or inward growth into the soft tissue or bone
If the tumor is a mucosal lesion, such as in the mouth or throat, the macules, plaques, or tumors may appear to be blue or violet.
A gastrointestinal Kaposi lesion may cause bloody stools. These lesions are, however, normally symptomless. They may rarely be associated with pain, diarrhea, or physical obstruction.
If the lining of the lungs is affected, this can lead to shortness of breath due to blockage. A bleeding lesion on the lung may leak blood into the mucus that is coughed up by the patient.
The different types tend to have different clinical presentations:
- HIV-associated Kaposi sarcoma is more aggressive than others and usually produces multiple lesions, often on the face and trunk. Internal tumors are also common.
- Classic or Mediterranean Kaposi sarcoma normally results in a small number of lesions, usually on the skin of the lower limbs, and particularly on the ankles and soles of the feet. The skin lesions are slow growing when compared with other forms. This type rarely occurs as an internal tumor.
- Endemic Kaposi sarcoma tends to affect younger people under 40 years of age, including children. Some forms appear identical to classic Kaposi, and others affect the lymphatic system and internal organs.
- Immunosuppressive treatment-related Kaposi sarcoma can appear more suddenly. It is often confined to the skin, but not always.
A suspected lesion of Kaposi sarcoma on the skin can be confirmed by laboratory examination of a sample, typically obtained by punch biopsy.
If internal tumors are suspected or are considered likely, such as in patients with HIV infection or AIDS or other immunosuppression, tests may include:
- CT or X-ray scans of the chest and abdomen
- gastrointestinal endoscopy
There is no routine way to check for Kaposi sarcoma, and often more than one lesion can appear at once, making early detection of an isolated tumor difficult. People who are at risk, such as those with suppressed immune systems, may regularly be examined to check for Kaposi sarcoma.
Unlike other cancers, Kaposi sarcoma is not staged using the typical system. Staging is a process that describes the location, size, and spread of a cancer. For HIV-related Kaposi sarcoma, however, physicians typically use the AIDS Clinical Trials Group (ACTG) system to stage the progression of the underlying disease.
The ACTG system looks at:
- the extent of the tumor (T)
- the status of the immune system (I) using the number of CD4 cells
- the extent of involvement within the body or systemic illness (S).
Kaposi tumors that do not cause pain do not often need treatment.
Some of the treatment options for Kaposi sarcoma are common to other types of cancer, such as:
Unlike almost all other cancers, treatment for Kaposi sarcoma focuses on maintaining the health of the immune system. This typically involves targeting HIV viruses or immunosuppressant drug use.
Highly active antiretroviral therapy (HAART) is a combination of anti-HIV drugs that are more effective in treating Kaposi sarcoma alongside chemotherapy than treatments that only make use of chemotherapy.
This is relevant only to tumors in people with stage 3 HIV. The success of this treatment lies in improving immunity by reducing the HIV load.
Treatment options include chemotherapy and immunotherapy.
In people with immune system suppression caused by drugs, such as those taking immunosuppressors following an organ transplant, Kaposi sarcoma can be treated by switching or decreasing the drug intake.
Local therapies for Kaposi sarcoma include surgical excision, cryotherapy, and electrocoagulation.
Radiation therapy is applied directly to lesions when multiple lesions are present or affecting lymph nodes. Imiquimod cream, which combats viruses and strengthens the immune system, is sometimes used as a local treatment for superficial tumors, such as in people with classic Kaposi sarcoma.
Chemotherapy drugs, such as vinblastine, can be used locally for Kaposi sarcoma and are injected directly into the tumor.
Researchers are also investigating other types of localized treatment however, such as sodium tetradecyl sulphate, as many people experience undesirable side effects with vinblastine. Intravenous chemotherapeutic drugs may be used for more aggressive forms of cancer.
Immunotherapy for Kaposi sarcoma harnesses the power of the immune system to attack cancer cells. Interferon alpha is one form of immunotherapy, injected into the muscle to help with immunity. It was one of the first drugs used against Kaposi sarcoma.