Kaposi sarcoma is a rare tumor that is named after the dermatologist who first described it in 1872, Dr. Moritz Kaposi.1 It has numerous types, the most common of which is associated with AIDS. All forms of Kaposi sarcoma are caused by a type of herpesvirus, Kaposi sarcoma herpesvirus (KSHV).2
Most people infected with KSHV do not develop Kaposi sarcoma unless their immune system is suppressed. The incidence of Kaposi sarcoma increased 20-fold during the AIDS epidemic in the early 1990s and this type of cancer is still seen most often in people with HIV/AIDS, as well as in people taking immunosuppressant medications.11
Kaposi sarcoma is characterized by the growth of abnormal tissue under the skin, in the lining of the mouth, nose, and throat or in other organs. These patches are typically purple or red in color and can bleed (which can cause problems if they develop in the digestive tract or lungs). Although usually asymptomatic, Kaposi sarcoma can be painful in some cases.
Medical News Today has a page dedicated to other types of sarcoma, which also affect soft tissues.
Contents of this article:
There are introductions at the end of some sections to recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Here are some key points about Kaposi sarcoma. More detail is in the body of this article.
- Kaposi sarcoma is a type of cancer that originates from the lining of blood vessels and lymphatic vessels (endothelial cells).
- Kaposi sarcoma can occur at numerous sites of the body, often presenting as lesions on the skin.
- The tumor is caused by the human herpesvirus 8 (HHV8), also known as the Kaposi sarcoma herpesvirus (KSHV).
- KSHV is normally held in check by the immune system, but people with compromised immunity, such as transplant patients, seniors and people with HIV/AIDS, are more likely to develop Kaposi sarcoma.
- Early in the AIDS crisis, patients infected with HIV in the US had around a 1 in 2 chance of developing Kaposi sarcoma. The advent of antiretroviral drugs has significantly decreased the rate to just six cases per million people each year.
- People infected with HIV who develop Kaposi sarcoma are diagnosed with AIDS - it is an AIDS-defining illness (although some are beginning to question this) and the most common malignancy of the syndrome.
- Diagnosis of suspected skin lesions is confirmed by punch biopsy. X-rays, colonoscopy, endoscopic examination and other tests may be used to detect internal lesions.
- Physicians will sometimes want to regularly screen for Kaposi sarcoma in people with HIV/AIDS.
- Treatments are usually local and include surgical removal of lesions, radiation therapy and locally injected chemotherapy. Biologic (immunotherapy) may also be used.
- As with other forms of cancer, more aggressive Kaposi sarcoma can be treated with wider radiation or systemic chemotherapy.
- In cases associated with immune suppression, treatment may take the form of antiretroviral drugs to manage HIV, or cessation or reduction of immunosuppressant medications, as appropriate.
What is Kaposi sarcoma?
Kaposi sarcoma is caused by human herpesvirus 8, an infection most likely to become problematic in people with compromised immune systems.
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 which 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 (KS):1-3
- Classic KS - also known as Mediterranean Kaposi sarcoma as it occurs mainly in older people of Mediterranean, Eastern European, and Middle Eastern heritage. It is more common in males than females.
- Epidemic KS - the most common form of KS, also known as AIDS-associated Kaposi sarcoma
- 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 infection
- Iatrogenic KS - also known as immunosuppressive treatment-related Kaposi sarcoma, immunosuppressive Kaposi sarcoma or transplant-related Kaposi sarcoma.
Kaposi sarcoma is an AIDS-defining illness in people infected with HIV, and the most common malignancy associated with the syndrome.4 The appearance of Kaposi sarcoma lesions is often what triggers a diagnosis of AIDS.1,2
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 an AIDS-defining illness.12
Cause of Kaposi sarcoma
Confirmation of the cause of Kaposi sarcoma came relatively recently due to the association between the lesions and HIV/AIDS. Although some physicians had long suspected (since the 1950s) that an infectious agent was the cause of Kaposi sarcoma, it was only in the wake of the HIV/AIDS epidemic that this theory was seriously explored.5
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).5,6
Most of us are infected with at least one type of herpesvirus, but a healthy immune system can usually keep these in check. The Kaposi sarcoma-associated herpesvirus is the eighth and most recently discovered type of herpesvirus.5,6
Almost all Kaposi sarcoma lesions contain viral DNA from HHV8.5,6
While the growth of Kaposi sarcoma almost certainly requires herpesvirus 8, exactly how the virus causes the tumor is still under investigation.6-8
Human herpesvirus 8 has numerous modes of transmission. It can be spread both sexually and non-sexually, including through organ transplantation and breastfeeding.4
HHV8 infection appears to be more easily spread through certain types of sexual activity, including oral-anal and oral-genital contact and deep-kissing (KSHV is present in saliva). Rates of HHV8 infection are much higher in men who have sex with men, compared to the general population.
As rates of HIV are also typically higher in this group, and HIV infection can compromise immunity, the incidence of Kaposi sarcoma is also higher in men with HIV/AIDS.2
People infected with HIV whose CD4 cell counts drop below 200 cells/microliter are at a higher risk of Kaposi sarcoma. However, some cases of Kaposi sarcoma have been seen in people with HIV whose CD4 cell count is above 300 cells/microliter.9,12
Other immunocompromised people are also more prone to herpesvirus 8 infection and subsequent Kaposi sarcoma - organ transplant recipients taking immunosuppressant drugs to suppress rejection of the organ, and seniors whose immunity has declined, for example.2
Endemic Kaposi sarcoma occurs in people living in Equatorial Africa and is, therefore, sometimes called African Kaposi sarcoma. Infection with herpesvirus 8 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.3
Due to a high rate of HIV/AIDS in Africa, epidemic Kaposi sarcoma is now the most common type of Kaposi sarcoma, not the endemic type.
Symptoms of Kaposi sarcoma
People with Kaposi sarcoma do not always present signs or symptoms of the cancer. In many people, however, asymptomatic skin lesions are indicative of the disease.2,10
Kaposi sarcoma often presents as cutaneous lesions, marks on the skin that are:2,10
- Brown, purple, pink or red macules (raised blemishes or blotches)
- May merge into plaques and nodules that range in appearance from blue-violet to black
- Sometimes show edema (swelling) and sometimes grow outward, or inward into the soft tissue or bone.
Kaposi sarcoma can sometimes present as a mucosal lesion in the mouth or throat.
If the tumor is a mucosal lesion, such as in the mouth or throat, the macules, plaques or tumors may appear blue to violet.2,10
If the Kaposi sarcoma is a gastrointestinal lesion, it may bleed (a physician may check stool to identify occult - hidden - bleeding). Otherwise, these lesions tend to be symptomless, although they can be associated with pain, diarrhea or an obstruction.2,3,10
If the lining of the lungs is affected, this can lead to shortness of breath due to blockage. If the lesion bleeds, this may be seen in sputum coughed up by the patient.2,3,10
The different forms of Kaposi sarcoma tend to have different clinical presentations:1-3
- AIDS-associated Kaposi sarcoma is a more aggressive form that usually shows as a number of skin lesions, often on the face and trunk. Internal tumors are also common
- Classic/Mediterranean Kaposi sarcoma is usually only a small number of lesions and usually on the skin of the lower limbs, particularly the ankles and soles of the feet. Compared with other forms, the skin lesions are slow-growing. This type rarely manifests as an internal tumor
- Endemic/African 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
- Iatrogenic/immunosuppressive treatment-related Kaposi sarcoma can appear more suddenly. It is often, but not always, confined to the skin.
Tests and diagnosis of Kaposi sarcoma
A suspected lesion of Kaposi sarcoma on the skin can be confirmed by laboratory examination of a sample, typically obtained by punch biopsy.2,3,10
Researchers are currently investigating the use of skin ultrasound for non-invasive detection of Kaposi sarcoma lesions.14
If internal tumors are suspected or are considered likely, such as in patients with HIV infection or AIDS or other immunosuppression, tests may include:2,3,10
- CT (computerized tomography) scan or X-ray of the chest and abdomen
- Bronchoscopy lung examination
- Gastrointestinal endoscope examination.
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. Patients who are more susceptible - for example, patients under treatment for HIV/AIDS - may regularly be examined to check for Kaposi sarcoma.2,3,10
Unlike other cancers, Kaposi sarcoma is not typically staged. Staging is a process that describes the cancer's location, size and extent of spread. For AIDS-related Kaposi sarcoma, however, physicians typically use the AIDS Clinical Trials Group (ACTG) system to stage AIDS.7,10
The ACTG system looks at:
- The extent of the tumor (T)
- The status of the immune system (I) (a CD4 cell count)
- The extent of involvement within the body or systemic illness (S).
Treatments for Kaposi sarcoma
Painless tumors ("indolent") can often be left untreated.2
Some of the treatment options for Kaposi sarcoma are common to other types of cancer, such as:
- Local therapy, including surgery
- Radiation therapy
- Biologic therapy (immunotherapy).
For patients with AIDS, HAART is more effective in treating Kaposi sarcoma than chemotherapy alone.
Unlike with almost all other cancers, treatment for Kaposi sarcoma focuses on maintaining the health of the immune system; this typically involves targeting HIV infection or immunosuppressant drug use.3
Highly active antiretroviral therapy (HAART) is a combination of anti-HIV drugs that, added to chemotherapy, is more effective in treating Kaposi sarcoma than chemotherapy alone.
Of course, this is relevant only to tumors in people with AIDS. The success of this treatment is most likely the result of improved immunity as HIV load decreases.2,7,8
In people with immune-system suppression caused by drugs, such as organ transplant patients, Kaposi sarcoma may be treated by switching or decreasing the drugs (where possible).2,3
Local therapies for Kaposi sarcoma include surgical excision, cryotherapy and electrocoagulation. Radiation therapy applied locally to lesions is used for multiple lesions or those affecting lymph nodes.2,3 Imiquimod cream, which has antiviral, antitumoral and immune increasing properties, is sometimes used as local treatment for superficial tumors, such as in classic Kaposi sarcoma.2
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 (such as sodium tetradecyl sulfate), however, as around 50% of people experience undesirable side effects with vinblastine.13 Intravenous chemotherapeutic drugs may be used for more aggressive forms of the cancer.2,5
Biologic therapy for Kaposi sarcoma harnesses the power of the body's own defense systems to attack cancer cells. Interferon alpha is one form of biologic therapy (immunotherapy) that is injected into the muscle to help with immunity. It was one of the first drugs to be used against Kaposi sarcoma.3
A molecule found in the urine of pregnant women blocks the growth of a variety of cancers, including Kaposi sarcoma - the AIDS-related cancer that currently has no cure - according to scientists at the University of Montreal in Canada.
A 2014 study published in the journal PLOS Pathogens found new clues about the cause of Kaposi sarcoma. The discovery lays the foundation for developing drugs that prevent Kaposi sarcoma and other related cancers.