Scientists Get Handle on Kaposi's Sarcoma
Herpes virus infects body before cancer takes hold
FRIDAY, Feb. 4, 2005 (HealthDay News) -- In a potential bit of good news for people with AIDS, researchers think they're coming closer to understanding how a virus attacks the immune system and sets the stage for the disfiguring kind of cancer called Kaposi's sarcoma.
The cancer, which can be fatal, was rare until the 1980s, when it began to take advantage of the weakened immune systems of AIDS patients. The telltale Kaposi's lesions frequently appear on the face, often making it obvious that someone has AIDS.
The findings, reported in the Feb. 3 issue of Science, won't immediately lead to a new treatment for Kaposi's sarcoma, said study co-author Dr. Don Ganem, a professor of medicine at the University of California at San Francisco. However, "this is the beginning of understanding," he said.
Few AIDS patients in the United States and Western European countries develop Kaposi's sarcoma anymore because a new generation of powerful drugs helps boost weakened immune systems, Ganem said. But Kaposi's sarcoma continues to threaten AIDS patients in Africa and other parts of the world where the drugs are as not widely available. Also, Kaposi's sarcoma continues to infect elderly men in the Mediterranean region who are not HIV-positive, Ganem said.
The cancer can strike the skin, causing ugly lesions, or -- more dangerously -- attack the lungs and internal organs.
Before Kaposi's sarcoma develops, a person must be infected by a germ called Kaposi's sarcoma-associated herpesvirus, which is related to the virus that causes genital herpes. It isn't clear how the virus spreads; it's more common in gay male AIDS patients than in heterosexuals, suggesting that homosexual sex may play a role.
The herpes virus often doesn't cause any symptoms and can remain dormant in the body for a long time, like the germs that cause shingles several decades after someone has a case of chicken pox, said Dr. Henry B. Koon, an instructor of medicine at Beth Israel Deaconess Medical Center/Harvard Medical School who studies Kaposi's sarcoma.
However, AIDS infection seems to wake up the herpes virus, and the cells that house the germs "not only make more virus, but they also form tumors," Koon explained.
Ganem and his colleague, Craig McCormick, investigated how the virus takes hold in the body. Although some of the virus's strategies remain a mystery, the researchers think they've discovered a communications pathway that helps the germs call in elements of the immune system known as cytokines.
In the immune system's intricate military operation, the cytokines serve a variety of roles, Ganem said. They act as a signal corps, directing soldier cells to the sites of problems, and also serve as a kind of weapon that can be used to attack enemies, he said.
The virus boosts the production of cytokines, Ganem said. This may seem like an odd approach, but it might serve to call in other immune system cells that the virus wants to hijack, he said. "It may be that it's just trying to attract more uninfected cells to the neighborhood and take them over," he added.
The next step in research is to gain more understanding of how the virus leads to cancer and to develop better treatments to stop it from spreading throughout the body, Ganem said.
While doctors can often easily treat Kaposi's sarcoma tumors in the skin, they sometimes must turn to chemotherapy and radiation. "The chemotherapy is pretty toxic, and not always effective," said Ganem, adding that a treatment to block the communications pathway could help patients.
To learn more about Kaposi's sarcoma, try the American Cancer Society.