Kaposi’s sarcoma is a type of cancer that forms unusual growths on the skin and inside the body, appearing as purple, red, or brown patches that can affect anyone with a weakened immune system.

Kaposi’s sarcoma represents a unique form of cancer that develops in the cells lining blood vessels and lymphatic channels throughout the body. Unlike many other cancers that start in one location and then spread, this condition can appear in multiple places at the same time. The disease creates visible changes on the skin called lesions, which are abnormal areas of tissue that can look like bruises but don’t fade when pressed.^[1]

What makes this cancer particularly distinctive is its connection to a virus and the immune system. The lesions often first appear on the face, arms, or legs, but they can also develop inside the mouth, in the digestive system, or within the lungs. These growths may start very small and flat, almost harmless-looking, but they can grow larger and cause serious health problems depending on where they form and how the body’s defenses respond.^[2]

How Common Is Kaposi’s Sarcoma

Kaposi’s sarcoma remains a relatively rare disease in most parts of the world. In the United States, fewer than 5,000 people are living with this condition, with the incidence rate staying stable at around 1 in 100,000 people since 1997.^[2][3] However, the disease shows dramatically different patterns across various populations and geographic regions.

The distribution of Kaposi’s sarcoma closely mirrors where the causative virus is most common. In certain parts of Sub-Saharan Africa, particularly countries near the equator like Uganda, Tanzania, Cameroon, and Congo, the disease occurs much more frequently. Before the AIDS epidemic, the incidence in these regions could exceed 6 per 1,000 person-years. The rates of infection with the responsible virus among children in Africa vary widely, from as low as 2% in Eritrea to nearly 100% in the Central African Republic.^[3][10]

Gender plays a significant role in who develops this cancer. Men are affected far more often than women, with classic forms of the disease showing a male-to-female ratio of approximately 10 to 15 men for every one woman. In some forms, this ratio can be as high as 17 men to one woman.^[3][10] Age also matters, with most cases occurring in people between 40 and 70 years old, though the endemic African form can affect much younger individuals, including children.

Among people with HIV/AIDS, Kaposi’s sarcoma was once extremely common, affecting over 35% of those with AIDS. However, the introduction of highly active antiretroviral therapy has dramatically reduced both the occurrence and severity of the disease in this population.^[5][14] The condition also appears in people who have received organ transplants and must take medications that suppress their immune system.

What Causes This Disease

The root cause of Kaposi’s sarcoma is infection with a virus called human herpesvirus 8, also known as HHV-8 or Kaposi sarcoma-associated herpesvirus. This virus is present in the lesions of all patients with Kaposi’s sarcoma, regardless of which type they have.^[1][3] When HHV-8 infects the cells that line blood and lymphatic vessels, it can transform these healthy cells into cancerous ones.

However, having HHV-8 alone is not enough to cause Kaposi’s sarcoma. Most people who carry this virus never develop the cancer because their immune system keeps the infection under control. The virus requires additional factors to trigger the development of disease. These factors, called cofactors, can include certain proteins or cytokines, which are substances released by cells that affect the behavior of other cells. This is why the virus causes problems primarily in people whose immune defenses are compromised.^[3]

In healthy individuals with strong immune systems, HHV-8 infection typically causes no symptoms at all because the body’s defenses prevent the virus from causing harm. It’s only when the immune system becomes weakened that the virus can lead to the uncontrolled growth of abnormal cells that characterize Kaposi’s sarcoma.^[1]

The virus spreads primarily through bodily fluids. It is mostly transmitted as a sexually transmitted infection, which explains why certain sexual practices increase the risk of acquiring both HHV-8 and developing Kaposi’s sarcoma. The virus can also pass between people who share needles for drug use. In some parts of the world, particularly in Africa where the virus is very common, transmission may occur through other routes, possibly including saliva-sharing practices.^[6]

Risk Factors for Developing Kaposi’s Sarcoma

Several factors significantly increase a person’s likelihood of developing Kaposi’s sarcoma. The most important risk factor is having a weakened immune system combined with HHV-8 infection. This immune suppression can occur in different ways, creating distinct patterns of disease.

People living with HIV, the virus that causes AIDS, face substantially elevated risk. Before effective HIV treatments became available, Kaposi’s sarcoma was one of the most common cancers in people with AIDS. The virus destroys immune cells, allowing HHV-8 to trigger cancer development. Men who have sex with men and bisexual men have higher risk, likely because they face increased chances of acquiring both HHV-8 and HIV.^[2]

Individuals who have undergone organ transplantation also face increased risk. After receiving a transplanted organ, patients must take medications called immunosuppressants to prevent their body from rejecting the new organ. These drugs intentionally weaken the immune system, which can allow HHV-8 to cause Kaposi’s sarcoma if the person carries the virus.^[1][2]

Age represents another risk factor, with the disease occurring most commonly between ages 40 and 70. Older adults appear more vulnerable, particularly for the classic form of the disease.^[2] Ethnic background also matters. People of Mediterranean, Southwest Asian, Eastern European, or Ashkenazi Jewish descent have higher rates of the classic form of Kaposi’s sarcoma.^[2][3]

Geographic location plays a crucial role in risk. People living near the equator in Sub-Saharan Africa face much higher rates of both HHV-8 infection and Kaposi’s sarcoma. This endemic form can affect both children and adults in these regions, suggesting that environmental factors or practices specific to these areas may contribute to transmission and disease development.^[2][10]

Sexual activity patterns influence risk as well. Unprotected sex increases the chances of contracting HHV-8 and HIV, as these viruses spread through bodily fluids exchanged during sexual contact. This explains why certain sexual practices are associated with higher rates of infection.^[2]

Recognizing the Symptoms

The symptoms of Kaposi’s sarcoma vary considerably depending on where the lesions appear in the body. Many people first notice changes on their skin, which is the most common location for this cancer to appear. These skin changes typically begin as small, flat spots that don’t cause pain or itching. They might seem harmless at first glance, resembling ordinary bruises.^[6]

However, these spots differ from regular bruises in important ways. When you press on them, they don’t lose their color as a normal bruise would. The lesions can appear in various colors, including purple, red, brown, or blue. As they grow over time, they may begin to rise above the surrounding skin and can merge together to form larger areas. Eventually, some lesions develop into raised bumps or nodules that can become ulcerated and bleed.^[1][6]

The face, arms, and legs are the most frequent locations for these skin lesions to first appear, though they can develop anywhere on the body. They may also form in the genital area or inside the mouth. The speed at which these skin changes progress varies greatly. Some people experience very slow growth with no visible changes for months, while others see rapid progression with new lesions appearing weekly.^[1][6]

When lesions form inside the mouth, eating can become painful. This can lead to difficulties maintaining proper nutrition if the condition progresses. Lesions in the digestive system can cause belly pain, blood in the stool, constipation, diarrhea, or vomiting. These symptoms occur because the abnormal growths interfere with the normal functioning of the digestive organs.^[2][9]

Kaposi’s sarcoma affecting the lungs produces respiratory symptoms. People may experience shortness of breath, persistent coughing, or even coughing up blood. These symptoms develop when lesions grow inside the airways or lung tissue, blocking normal breathing or causing bleeding.^[2][9]

Swelling represents another important symptom. When Kaposi’s sarcoma lesions form in or near lymph nodes, they can block the normal flow of lymph, the clear fluid that circulates through the body’s lymphatic system. This blockage causes fluid to build up in tissues, creating painful swelling called lymphedema. This swelling most commonly affects the arms or legs and can become quite uncomfortable. The earlier this complication is identified and addressed, the easier it is to manage.^[2][6]

Preventing Kaposi’s Sarcoma

While there is no guaranteed way to prevent Kaposi’s sarcoma, certain actions can significantly reduce your risk of developing this cancer. Prevention strategies focus primarily on avoiding HHV-8 infection and maintaining a healthy immune system.

The most important preventive measure involves protecting yourself from HIV infection. Since HIV weakens the immune system and allows HHV-8 to cause cancer, following safe practices to prevent HIV transmission can indirectly protect against Kaposi’s sarcoma. This includes practicing safe sex through consistent condom use and avoiding sharing needles if using drugs.^[1]

For people who are already living with HIV, taking antiretroviral medications as prescribed is crucial. These treatments keep the HIV virus under control, allowing the immune system to function more normally. When HIV is well-controlled through medication, the risk of developing Kaposi’s sarcoma drops dramatically. In fact, highly active antiretroviral therapy both prevents and often successfully treats Kaposi’s sarcoma in people with HIV/AIDS.^[5][8]

People who have received organ transplants face a unique situation. They need immunosuppressant medications to protect their transplanted organ, but these same drugs increase their risk for Kaposi’s sarcoma if they carry HHV-8. In some cases, doctors may reduce or adjust these medications if Kaposi’s sarcoma develops, though this must be balanced carefully against the risk of organ rejection. Research has shown that switching from certain immunosuppressants to alternative drugs may help, as some medications appear to have protective effects against the cancer.^[3][15]

Avoiding practices that could transmit HHV-8 is important, though this can be challenging since the virus spreads through bodily fluids, including during sexual contact. Being aware of this risk and discussing it with healthcare providers can help people make informed decisions about their health.^[2]

Regular medical checkups are valuable for people at higher risk. Those with HIV, organ transplant recipients taking immunosuppressants, and people from high-risk ethnic backgrounds or geographic regions may benefit from regular skin examinations. Early detection of lesions allows for prompt treatment, potentially preventing more serious complications.^[2]

How the Disease Affects the Body

Understanding how Kaposi’s sarcoma changes normal body functions helps explain why the disease causes its particular symptoms and complications. The cancer begins at the cellular level when HHV-8 infects the endothelial cells that form the inner lining of blood vessels and lymphatic vessels throughout the body.

The virus carries genetic material that interferes with how these cells normally operate. HHV-8 produces proteins that disrupt the cell’s usual controls on growth and division. In a healthy cell, various mechanisms ensure that growth occurs only when needed and stops when appropriate. The virus essentially breaks these safety mechanisms, allowing cells to multiply uncontrollably.^[3]

As these infected cells multiply, they don’t form normal blood vessel tissue. Instead, they create abnormal growths composed of cancerous cells, newly formed blood vessels that don’t function properly, red blood cells that leak out of these malformed vessels, and white blood cells that respond to the abnormal tissue. This mixture creates the characteristic purple, red, or brown color of Kaposi’s sarcoma lesions, caused by blood and iron pigments accumulating in the tissue.^[8]

The abnormal blood vessels in these lesions are fragile and poorly constructed. They can break easily, which explains why the lesions sometimes bleed. These malformed vessels also leak fluid into surrounding tissues. When lesions form near or within lymph nodes, they can physically block the lymphatic channels, preventing the normal drainage of lymph fluid. This blockage causes fluid to accumulate in tissues, producing the painful swelling of lymphedema.^[6]

When lesions develop in internal organs, they disrupt normal organ function through several mechanisms. In the digestive system, growths can physically block the passage of food or cause bleeding when the fragile abnormal vessels break. In the lungs, lesions can interfere with gas exchange, making it harder for oxygen to enter the bloodstream and carbon dioxide to be expelled. They can also obstruct airways, causing breathing difficulties and coughing.^[2]

The disease behaves differently from many other cancers because it can start in multiple locations simultaneously rather than spreading from a single original tumor. This happens because HHV-8 can infect vessel-lining cells anywhere in the body, and in someone with a weakened immune system, multiple infected sites can progress to cancer independently.^[8]

The immune system’s state dramatically influences disease progression. In people with relatively preserved immune function, the body can sometimes control the cancer’s growth, leading to slow progression or even periods of stability. However, in severely immunocompromised individuals, such as those with advanced AIDS or those taking high doses of immunosuppressants, the disease can progress rapidly and aggressively because the immune system cannot mount an effective response against the abnormal cells.^[1]

Complications arise when the cancer interferes with vital functions. Extensive lymphatic involvement can cause severe swelling and discomfort. Widespread lung involvement can lead to life-threatening breathing problems. Digestive tract lesions can cause dangerous bleeding or obstruction. The cancer can also cause anemia, a condition where the body doesn’t have enough healthy red blood cells, either through chronic bleeding or through the effects on bone marrow where blood cells are made.^[2]