Magazine article Science News

Cancer Virus Redux; Viruses Were Once a Hot Subject of Cancer Research; after a Decade out of the Limelight, They're Back Again

Magazine article Science News

Cancer Virus Redux; Viruses Were Once a Hot Subject of Cancer Research; after a Decade out of the Limelight, They're Back Again

Article excerpt

When the U.S. government declared its "war on cancer" in 1971, viruses were considered to be among the most likely cancer-causing agents. The National Cancer Institute (NCI) in Bethesda, Md., had a special program to screen tumor cells for the presence of virus particles, but, says current NCI head Vincent T. DeVita, "it wasn't to be that simple."

Despite expense and effort, no one was able to isolate a cancer virus from human tumor cells during that initial push; there arose "a lot of skepticism about viruses as a cause of cancer," DeVita sys today. Some researchers dropped out of the field; others shifted their emphasis to basic virology research.

"Out of that [shift] emerged the basic ability to isolate viruses that we didn't have in the beginning," says DeVita. "We're now back in the business of finding viruses [as a] cause of cancer," he said at the recent American Cancer Society's science writers' seminar in san Diego. Researchers there described virus-cancer connections ranging from epidemiological links--coincident occurrences of a virus and a type of cancer in a given population--to direct laboratory observations of a virus transforming normal cells into cancerous ones.

Viruses have been fingered in liver cancer, the most common cancer in the world; cervical cancer; Burkitt's lymphoma; nasopharyngeal carcinoma; and an adult T cell leukemia. But researchers are quick to caution that though these cancers are believed to be caused by viruses, they don't spread as easily as common viruses spread--for example, with a sneeze. "We have not found that kind of transmission of cancer viruses," says DeVita. "You need very intimate contact to spread the viruses that we know can be spread. None of it seems to be easy, thank God."

Virus-associated cancers are more common in less developed nations, DeVita notes. Differences in hygiene may be one reason, he suggests, with individuals exposed at an earlier age, giving cancer viruses a longer time to act. The virus-associated cancers, which tend to occur earlier in life, also wind up representing a greater proportion of total cancers in these countries, possibly because people in less developed countries are more likely to die before getting the "old age" cancers like cancer of the urinary tract, bladder and gut wall.

Cervical cancer was an early candidate for a virus-caused cancer because it seems to be transmitted venereally. The most popular culprit was herpes simplex virus. But after years of failed attempts at isolating herpesviruses from cervical cancer cells, researchers discarded the herpes option in favor of the papillomavirus.

Papillomaviruses cause warts, from common skin warts to cervical and penile warts. But while warts on the hands and feet have never been known to progress to cancer, cervical warts can go on after many years to become cancerous, says Richard Schlegel of the NCI's Laboratory of Tumor Virus Biology.

The cervical warts are venereally transmitted, as the cancer appears to be--cervical cancer is associated with other venereal diseases, multiple sex partners and the early onset of sexual activity.

Schlegel and his colleagues tested cells from eight patients with cervical cancer and found that two particular members of the papillomavirus family predominated in six. The viruses were in an active state--the researchers found viral mRNA, indicating the viruses were directing protein production. When they screened cells from other types of cancer, they were unable to find the virus. One of the two viruses apparently disturbs normal cell division and in this way may lead to cancer, says Schlegel.

But the case isn't closed for the papillomaviruses. Many women with no tissue abnormalities harbor the virus in cervical cells; it could be that the virus is present in the tumor cells as an innocent passenger. "It's difficult to tell if it's a cause or latent infection," says Schlegel. …

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