Kaposi's sarcoma produces pink, purple, or brown tumors on the skin, mucous membranes, or internal organs. It was a very rare form of cancer, primarily affecting elderly men of Mediterranean and eastern European background, until the 1980s, when it began to appear among AIDS patients. Milder forms of the disease can be managed successfully with topical agents and therapies; widespread disease requires chemotherapy.
Investigators recognize four distinct forms of Kaposi's sarcoma (KS). The first form, called classic KS, was described by the Austrian dermatologist Moriz Kaposi more than a century ago. Classic KS usually affects older menof Mediterranean or eastern European backgrounds by producing tumors on the lower legs. Though at times painful and disfiguring, they are not generally life-threatening. The second form of the disease, African endemic KS, primarilyaffects boys and men. It can appear as classic KS, or in a more deadly formthat quickly spreads to tissues below the skin, the bones and lymph system, leading to death within a few years of diagnosis. Another form of KS, iatrogenic KS, is observed in kidney and liver transplant patients who take immunosuppressive drugs to prevent rejection of their organ transplant. Iatrogenic KSusually reverses after the immunosuppressive drug is stopped. The fourth formof KS, AIDS-related KS, emerged as one of the first illnesses observed amongthose with AIDS. Unlike classic KS, AIDS-related KS tumors generally appearon the upper body, including the head, neck, and back. The tumors also can appear on the soft palate and gum areas of the mouth, and in more advanced cases, they can be found in the stomach and intestines, the lymph nodes, and thelungs.
A variety of factors appear to contribute to the development of KS:
- Genetic predisposition. People with classic KS, and those who develop the tumors after transplantation, are more likely than others to possess a geneticallydetermined immune factor called HLA-DR. Cases of KS that run in families, however, are rare.
- Sex hormones. The fact that the disease is more likely to afflict men than women suggests sex hormones, such as testosterone inmen, may stimulate the growth of KS tumors, and that estrogen in women may retard their growth.
- Immune suppression. Liver, kidney, and bone marrow patients who take immunosuppressive drugs to prevent transplant rejection frequently develop KS lesions. Similarly, KS has been observed in patients receiving systemic treatment with high-dose corticosteroids, which also suppresses the immune system. Immune suppression is the hallmark of AIDS.
- Infectious, sexually transmitted agent. AIDS-related KS is ten times more likely to appear in homosexual or bisexual men with AIDS than it is to appear in IV drug users, hemophiliacs, or women. In addition, the proportion of AIDS patients who develop KS has decreased markedly as safer-sex practices have become more widespread. A number of viruses have been proposed as possiblecauses. They include cytomegalovirus and human papilloma virus, fragments ofwhich have been found in KS tumor specimens. A more likely candidate, however, is a new herpes virus that has been called human herpes virus 8 (HHV-8) orKS-associated herpes virus (KSHV). Since fragments of the virus were first disclosed in KS samples in 1994, they have since been found in KS samples takenfrom patients with classic KS, African endemic KS, and KS in transplant patients. Fragments of HHV-8, however, have also been found in patients who haveother skin diseases but who do not have KS.
Many physicians will diagnose KS based on the appearance of the skin tumors and the patient's medical history. Unexplained cough or chest pain, as well asunexplained stomach or intestinal pain or bleeding, could suggest that the disease has moved beyond the skin. The most certain diagnosis can be achievedby taking a biopsy sample of a suspected KS lesion and examining it under high-power magnification. For suspected involvement of internal organs, physicians will use a bronchoscope to examine the lungs or an endoscope to view the stomach and intestinal tract.
There is no single best treatment for KS. Treatments range from topical agents for mild disease with few tumors to more aggressive systemic chemotherapy for more serious KS that has spread to large areas of skin or the internal organs. Physicians will frequently combine topical, radiation, and various systemic chemotherapy drugs, depending on the sites of the body affected, the speed at which it is progressing, and the patient's overall health, among other considerations.
When the number of KS tumors is small and the disease appears to be progressing slowly, physicians will consider destroying the lesions with cryotherapy (using a liquid nitrogen spray or probe to freeze the tumor); injections directly into the tumor of vinblastine (a drug also used for systemic chemotherapy); or radiation therapy targeted at the tumor sites.
With widespread KS lesions over the body surface, or evidence of spread to other parts of the body, physicians will consider systemic chemotherapy drugs,either alone or in a variety of combinations. Combination therapy generally produces a better response, with fewer toxic side effects associated with large doses of any single drug. Among the chemotherapy agents that physicians will consider using are vinblastine, bleomycin, and doxorubicin. A new class ofchemotherapy drugs, called liposomally encapsulated drugs, appears to producegood results with fewer toxic side effects than do more conventional chemotherapy drugs.
Evidence suggests that for some individuals, the class of AIDS drugs called protease inhibitors, in combination with other anti-HIV drugs, can reduce thelevels of detectable HIV in the blood to nearly zero, and in some patients stabilize or reverse KS tumors. More research is needed in this area. Since thediscovery of HHV-8, interest in an antiviral approach to KS has increased. There is no evidence, however, that two antiviral drugs commonly prescribed for herpes, acyclovir and ganciclovir, have any effect on the disease. One study of 20,000 patients with HIV and AIDS found that those who took foscarnet, another antiviral medication that works in a different way than acyclovir andganciclovir, were less likely to develop KS tumors.
A number of other treatments for KS are under investigation, including:
- Interferon-alpha. Interferon-alpha is made by the body and has powerful effects on the immune system. Investigators have tried injecting it directly into lesions, and also in combination with other anti-HIV drugs such as zidovudine, with some success.
- Retinoids. These derivatives of vitamin A have long been used to treat acne and other skin diseases. Investigatorsare evaluating both topical preparations of these drugs as well as systemic versions.
- Laser therapy. In patients with small tumors, some investigators report success using lasers to destroy KS lesions. The reappearance ofnew tumors, may be high, however.
The prognosis for patients with classic KS is good. Tumors can frequently becontrolled and patients frequently die of other causes before any serious spread. African endemic KS can progress rapidly and lead to premature death, despite treatment. In AIDS-related KS, milder cases can frequently be controlled; the prognosis for more advanced and rapidly progressing cases is less certain and dependent on the patient's overall medical condition. There are indications that KS can be stabilized or reversed in patients whose level of HIV inthe blood is reduced to undetectable levels via antiretroviral therapy.
Safer sex practices may help to prevent AIDS-related KS by decreasing the risk of transmission of HHV-8. Treatment with antiretrovirals and protease inhibitors may help to preserve the function of the immune system in HIV patientsand delay the appearance and progression of KS lesions.