Kaposi sarcoma is a cancer that forms in the lining of blood vessels and lymph vessels, producing distinctive reddish-purple or dark brown skin lesions. It is caused by infection with human herpesvirus 8 (HHV-8), but the virus alone isn’t usually enough to trigger the disease. Kaposi sarcoma develops when HHV-8 infection combines with a weakened immune system or chronic inflammation, making it unusual among cancers in that it doesn’t arise from a single transformation event but from the combined effects of a virus with blood-vessel-growing properties and an inflammatory environment.
How HHV-8 Leads to Cancer
HHV-8, sometimes called Kaposi sarcoma-associated herpesvirus, infects the cells that line blood and lymph vessels. Once inside, the virus produces proteins that stimulate three processes at once: inflammation, the growth of new blood vessels, and the conversion of normal lining cells into abnormal spindle-shaped cells. These spindle cells are the hallmark of Kaposi sarcoma tissue under a microscope.
What makes this cancer biologically unusual is that the tumor cells may not grow entirely on their own. They appear to depend on ongoing viral activity and the surrounding inflammatory signals to keep multiplying. This is one reason that restoring immune function, particularly in people with HIV, can sometimes cause lesions to shrink or disappear without direct cancer treatment.
The Four Types of Kaposi Sarcoma
Kaposi sarcoma isn’t a single disease profile. It occurs in four distinct clinical settings, each affecting different populations and behaving differently.
Classic Kaposi Sarcoma
This form appears primarily in men over 50 of Eastern European or Mediterranean descent, with a male-to-female ratio of about 17 to 1. Lesions typically develop on the lower legs and feet and tend to grow slowly over years. It is the least aggressive form and rarely spreads to internal organs.
Endemic (African) Kaposi Sarcoma
Found in sub-Saharan Africa, this type has an unusual predilection for children, in whom it often presents as generalized lymph node involvement rather than skin lesions. Its geographic distribution mirrors the high rates of HHV-8 infection in the region. Incidence is strikingly high in countries like Namibia, where the age-standardized rate reaches 21.2 per 100,000 men and 11.1 per 100,000 women, and Zambia, at 15.7 and 9.5 respectively.
AIDS-Related Kaposi Sarcoma
This is the most well-known form and the second most common tumor in people living with HIV. It is classified as an AIDS-defining illness, meaning its appearance signals advanced immune suppression, typically when a specific type of immune cell (CD4 T-cells) drops below 200 per cubic millimeter of blood. Unlike the classic form, AIDS-related Kaposi sarcoma can appear anywhere on the skin and frequently involves internal organs including the lungs, mouth, and digestive tract.
Iatrogenic (Transplant-Related) Kaposi Sarcoma
People taking immune-suppressing medications after organ transplantation face a 400- to 500-fold increased risk of developing Kaposi sarcoma compared to the general population. Over 5% of transplant patients who develop any new cancer will develop this one. The male-to-female ratio is about 3 to 1, and like the AIDS-related form, it can involve both skin and internal organs.
What the Lesions Look Like
Kaposi sarcoma lesions are among the more visually distinctive of any cancer. They typically appear as flat spots that are violaceous (a deep purple), reddish-blue, or dark brown. Over time, these lesions progress through three recognizable stages.
In the patch stage, lesions are flat with well-defined edges and may have a slightly scaly surface. They can be mistaken for bruises or other minor skin conditions. As they progress to the plaque stage, they become thicker and firmer, developing a violaceous-brown color that reflects the increased blood vessel growth underneath. On areas with thicker skin, like the soles of the feet, plaques can become notably scaly with tightly adherent white scales on top.
In the nodular stage, lesions become raised bumps that may grow outward from the skin surface, ulcerate, or bleed. Multiple lesions can appear simultaneously, and they may merge into larger areas of involvement. The progression from patch to nodule can take months to years depending on the type and the person’s immune status.
When It Spreads Beyond the Skin
Kaposi sarcoma can involve internal organs, particularly the gastrointestinal tract and lungs. GI involvement is especially tricky to detect because it often causes no symptoms at all. When symptoms do appear, they tend to be vague: nausea, vomiting, abdominal pain, or diarrhea. In severe cases, GI lesions can cause internal bleeding, bowel obstruction, or perforation.
Pulmonary involvement carries the most serious prognosis. Lung lesions can cause coughing, shortness of breath, or bloody sputum, and they are associated with significantly higher mortality. For people who have skin lesions or symptoms suggesting internal disease, endoscopy with biopsy is the primary tool for confirming whether the cancer has spread to the GI tract.
How It’s Diagnosed
Experienced clinicians can often recognize Kaposi sarcoma from its appearance alone, particularly in a patient with known HIV or immune suppression. However, a biopsy is needed for a definitive diagnosis. Under a microscope, the tissue reveals characteristic features: spindle-shaped cells forming slit-like spaces filled with red blood cells, scattered inflammatory cells, and deposits of iron-containing pigment from broken-down blood.
Early patch-stage lesions can be the hardest to confirm because they resemble other inflammatory skin conditions or minor blood vessel abnormalities. In uncertain cases, pathologists look for proteins produced by HHV-8 within the tissue to confirm the virus is present and driving the disease. Additional imaging or endoscopy may be performed to check for internal organ involvement, especially in the AIDS-related and transplant-related forms.
Treatment and What to Expect
Treatment depends heavily on which type of Kaposi sarcoma a person has and how far it has spread.
For AIDS-related Kaposi sarcoma, the most important first step is starting or optimizing antiretroviral therapy for HIV. Restoring immune function can produce dramatic results on its own. In one study, six of eleven patients with progressive Kaposi sarcoma achieved complete disappearance of their lesions after starting antiretroviral therapy, with complete responses occurring in a median of about six months. Three others had partial improvement. This makes immune restoration the foundation of treatment for anyone with HIV-associated disease.
For transplant-related cases, doctors may reduce or change the immune-suppressing medications when possible, balancing the risk of organ rejection against the need to let the immune system fight the cancer.
When the disease is widespread or progressing despite immune recovery, systemic chemotherapy becomes necessary. Two drugs are currently approved specifically for Kaposi sarcoma: a liposomal form of doxorubicin (a chemotherapy agent encapsulated in tiny fat particles to reduce side effects and improve delivery) and paclitaxel. These are used for advanced disease involving multiple skin sites or internal organs.
For limited skin disease, local treatments including radiation therapy, surgical removal, or injection of medication directly into lesions can control individual spots without the need for body-wide chemotherapy. Classic Kaposi sarcoma, because of its slow growth, often needs only local management or careful monitoring.