AIDS Has Helped to Prove Link Between Viruses and Cancers
Scientists since the turn of the century have suspected--but never quite proven--that viruses cause human cancers.
But recent research, inspired largely by the worldwide epidemic of AIDS, has shown that human viruses and some forms of cancer are, indeed, very intimately associated.
The recent discoveries that AIDS and a rare but deadly form of adult T-cell leukemia are caused by two newly discovered viruses belonging to the same family have once more heightened scientific interest in the role viruses seem to play in causing many types of malignancies, primarily cancers that seem to be sexually transmitted.
Franco-American Sponsorship
“There is a great sense of interest and concern in viruses and cancer. Viruses and cancer have come of age,” Dr. Peter Fischinger, deputy director of the National Cancer Institute, told an international conference here last week.
The conference, sponsored by the French Assn. for Cancer Research and the U.S. National Institutes of Health, was attended by scientists from Asia and both sides of the Atlantic who have spent decades tracking down evidence to link viruses to some forms of cancers, including liver cancer and cancer of the genitals.
Researchers now believe that most cancers of the cervix and genital cancers in males are closely associated with certain types of papilloma virus, the virus that causes warts.
Scientists also believe that the virus that causes hepatitis B, once known as serum hepatitis, very likely plays a major role in liver cancer, the principal cancer killer in much of Africa and Asia.
In addition, they believe that the Epstein-Barr virus, which is responsible for mononucleosis or “kissing disease” in the United States, is a triggering factor for a lethal lymphoma in African children and naso-pharyngeal cancer in China.
And finally, scientists here said, HTLV-I, the virus that causes adult T-cell leukemia in Southern Japan and the Caribbean, appears to contribute to a form of paralysis that strikes people in widely scattered parts of the world.
Like AIDS, each of these viruses, except the Epstein-Barr virus, can be transmitted sexually. “Cancer can now be considered to be sexually transmitted,” said Harvard’s Dr. William Haseltine.
According to Franco Rilke of Italy’s National Cancer Institute, papilloma virus infection of the genital tract is now the most common venereal disease.
Although at least 40 types of pappiloma are known, including the one that causes warts, only certain types have been associated with cancers of the cervix, vulva, penis and anus.
A Common Female Cancer
In the case of cervical cancer, one of the most common female cancers worldwide, scientists have detected portions of the pappiloma virus’ genetic material in the cancer cells of more than 90% of cervical cancer cases studied. This is taken by medical experts as strong evidence that the virus causes that disease.
Nevertheless, infection by the virus does not necessarily mean that cancer will occur. As with the AIDS virus, other factors--personal hygiene, for example, in the case of pappiloma viruses--may be involved, experts say.
While the deadly acquired immune deficiency syndrome is not itself a malignant disease, it is accompanied in 30% of cases by a skin cancer called Kaposi’s sarcoma. And the virus that causes AIDS (HTLV-III/LAV) shares characteristics with some of the other suspected tumor viruses.
One such characteristic is a tendency to remain dormant in cells for years before symptoms appear. The AIDS virus can have a latency period of three to five years while the HTLV-I, the adult T-cell leukemia virus, may take up to 30 years to cause disease.
Another similarity appears to be the need for some additional circumstance--called a co-factor--to be present, in addition to the virus, before cancer can occur.
For AIDS, no co-factor has yet been identified. But persistent infection by another virus--such as the hepatitis B virus--is strongly suspected.
The reason that Epstein-Barr virus causes the lethal lymphoma in young African children but less severe mononucleosis in American adolescents is believed to be due to co-factors present in Africa, according to Dr. A. Olufemi Williams of the Organization for African Unity. One such co-factor may be malnutrition, which is known to reduce the ability of the immune system to fight infection, he said.
“Almost never is this virus operating alone. It is almost always in association with other factors,” added Dr. Maurice Tubiana, a French authority from the Institute Gustave Roussy.
Grows on Peanuts
The same is also believed to be true for the hepatitis B virus in causing liver cancer in Africa. The chief co-factor suspected in that case, according to Williams, is aflatoxin, a carcinogenic mold that grows on peanuts, a chief food crop in Africa.
Liver and nasopharyngeal cancer also are among the leading types of cancer in China, where studies are under way to learn the roles played by the hepatitis and the Epstein-Barr viruses, said Dr. Y. Zeng of China’s National Center for Preventive Medicine.
It could be, some scientists say, that some individuals are genetically susceptible to specific types of cancer that are associated with viruses. These susceptibilities are related to so-called tissue types which, among other things, are involved in regulating the body’s immune system.
According to Dr. Walter Bodmer of Britain’s Imperial Cancer Research Fund Laboratories, the best known such association is between a certain tissue type and nasopharyngeal cancer occurring in southern China. Tissue types have also been associated with Burkitt’s lymphoma in Africa and Kaposi’s sarcoma, he said.
Human Vaccine
Of all the cancer-associated viruses, a human vaccine exists only for hepatitis B. As a preventive of hepatitis-associated liver cancer in the Third World, however, this vaccine is of limited use because of its excessive cost--about $100 per person.
A less expensive genetically engineered hepatitis B vaccine is now being developed and soon will be tried in Africa, according to Dr. M. A. Epstein of the University of Oxford.
Epstein, for whom the Epstein-Barr virus is named, is developing a vaccine for that virus which he said protects test animals against massive doses of the virus.
The hope, he said, is to vaccinate young African children in order to prevent Burkitt’s lymphoma.
Hopes for Protection
“Burkitt’s lymphoma is a multi-factorial disease like cigarettes and lung cancer,” he said. “We hope that by removing the virus, the vaccine will protect, like removing cigarettes does for lung cancer.”
Any vaccine or effective therapy for AIDS may be years away, although American researchers said headway is being made.
Fischinger, the National Cancer Institute deputy director, said that, although no vaccine has yet reached the animal stage of testing, an international team of investigators is working on one that should be ready for animal trials within months.
And Dr. Samuel Broder of the National Cancer Institute said an experimental drug called AZT also appears to be promising. While it is too early to know if AZT has therapeutic effect, in a test on 15 patients, it did result in an increase in the number of immune system cells of the type that are destroyed by the AIDS virus, he said.
