Progress on Cancer

Most researchers have long believed that viruses play some crucial role in causing human cancers. The source and precise function of these viruses (tiny packets of nucleic acids and protein) in cancer are still obscure, and no one knows how to control them. Dramatic progress cannot be made until cancer viruses are clearly identified in humans, as has already been done in animals. Now that vital next step has apparently been taken.

Because false grails have been hailed in the past, the U.S. scientists reporting the new development this week used guarded language. Further tests are scheduled to confirm the find, details of which are scheduled for publication in the British journal Nature. Still, Drs. Robert McAllister and Murray Gardner are willing to say: "We're almost certain that this is the virus we're after."

Self-Doubt. McAllister, of the Childrens Hospital of Los Angeles, and Gardner, of the U.S.C. School of Medicine, led the California team participating in the experiments. The National Cancer Institute also took part. The West Coast phase started in 1968 with the study of tissue from a seven-year-old girl suffering from rhabdomyosarcoma, a rare, generally fatal cancer that attacks the body's voluntary muscles. Though the child died, the doctors did manage to take a sample of her tissue and keep it growing in culture. Suspecting that these cancer cells contained viruses, the researchers tried to coax them out of the tissue with radiation, cancer-producing chemicals and even exposure to other viruses. These efforts proved unsuccessful.

The pace of the experiments picked up last spring when a solution made from the malignant cells was injected into unborn kittens. Four of the animals, all from different mothers, developed tumors. In effect, the cancers created were almost entirely of human cellular composition. One of the tumors was shedding C-type virus particles, similar to those known to cause cancer in animals, at a prodigious rate.

Despite these results, the researchers remained skeptical of their own evidence. "We thought it was just a feline leukemia virus," explained McAllister. But further experiments showed that the virus was chemically different from all previously identified mammalian viruses. Gardner still feels a "small nagging doubt--the remote possibility that it's a strange new type of cat virus." To rule out this possibility, the researchers plan an additional series of laboratory experiments, including attempts to produce viral antiserum from guinea pigs and rabbits. The antiserum could then be used in human cancer tissue to test for the presence of the newly discovered virus.

Earlier Detection. Viruses and virus-like particles have also been found in other forms of human cancer--in the breast, cervix and lymphatic system, for instance. But scientists thus far have been unable to determine whether any of these particles could cause cancer; this is what sets the new find apart from earlier ones and makes scientists hopeful of further progress. "If this proves to be a true human virus," says Dr. Robert Huebner of the National Cancer Institute's viral carcinogenesis branch, "it will mean that we're light-years ahead of where we've been. It means we've reached a point that we didn't expect to reach for years."

Huebner believes that identification of the virus can lead to development of tests for earlier detection of cancer. Firm identification can also help the investigation of complex molecular questions concerning the genetic origin of cancer viruses, how they may be activated by such environmental factors as cigarette smoke and radiation and how they trigger the uncontrolled cellular growth of cancer.

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