Viruses and Cancer

Doctors have long known that viruses can cause cancers in mice, cats and other animals. But can these microscopic packets of nucleic acids* also cause cancers in humans? Last week virologists attending a science writers' seminar sponsored by the American Cancer Society in St. Augustine, Fla., offered new arguments that they could. They provided no definite proof, but they did succeed in establishing a case of guilt by association.

Virologists offered as a prime suspect the herpes simplex Type 2 virus, a variant of the virus responsible for cold sores. Herpes 2, which causes infections in the genital tracts of both sexes, has been under intense scrutiny by scientists since 1966, when findings by Dr. Andre Nahmias of Atlanta's Emory University suggested that it might be involved in human cancer. Nahmias has since found high levels of antibody to the virus (which can transform normal cells into malignant ones in the test tube) in women with cervical cancer. He also established that women who have been infected with genital herpes--which can be transmitted during sexual intercourse --are eight times more likely to develop cervical cancer than women without such infections. (Women whose husbands suffer from cancer of the prostate also run an increased risk of developing not only uterine but breast cancers, according to researchers from New York's Columbia-Presbyterian Medical Center. They urged these women to undergo frequent checkups that would detect any malignancies early, when they can be most successfully treated.)

Outlaw Genes. Additional evidence against the herpes virus was offered last week by Dr. Albert Sabin, developer of the first live-virus polio vaccine. He has found antibodies specific to both the Type 2 and the cold sore (or Type 1) herpes simplex viruses in 183 patients suffering from 14 different cancers that account for about 25% of all human cancer deaths. These include malignancies of the skin, lip, larynx, kidney, prostate and cervix. Sabin could find no evidence of such viruses in 175 patients with such systemic cancers as leukemia and lung cancer or with malignancies of the breast, lung and stomach.

Others believe that viruses may cause systemic cancers too. Dr. Robert Gallo of the National Cancer Institute reported that his laboratory had succeeded in isolating from human leukemic cells an enzyme produced by a virus. The enzyme is not usually detectable in normal cells.

Other evidence implicating viruses was offered by Dr. Sol Spiegelman, director of the Institute of Cancer Research at Columbia University. His findings seem to prove that some cancers are caused by infectious--though probably not contagious--viruses rather than by hereditary factors. (Cancers can also be caused by such chemicals as asbestos and the tars in cigarette smoke and exposure to radiation.) Spiegelman first identified strands or sequences of leukemia-causing nucleic acids in the genetic material of eight leukemic patients and found that normal patients did not carry such abnormal DNA sequences in their cells. He then conducted an experiment to determine if the outlaw genes were inherited. Reasoning that identical twins would have identical genetic sequences, he searched until he found two sets of twins in which one partner was leukemic, the other not. In both cases, only the leukemic twin carried the abnormal DNA--a finding that convinced Spiegelman that whatever caused the disease was acquired after conception, probably by means of a virus.

Devil's Advocate. Spiegelman's findings--and those of fellow virologists --failed to persuade at least one of his colleagues at the seminar. Playing devil's advocate, Dr. Paul Black of the infectious-disease unit at Massachusetts General Hospital cautioned that the case against viruses was far from complete. Describing prevailing virus theories as "presumptuous," Black questioned whether the presence of a virus in tumor cells proved anything. Said he: "We still can't be sure whether viruses cause cancer or cancers cause viruses." He noted that some viruses not even suspected of causing cancer exist in close association with cancer cells. Mumps viruses, for example, have been found in the cells that result from Hodgkin's disease, a cancer of the lymphatic system; there is no evidence, however, that they cause the condition. Other viruses, he pointed out, persist in their hosts without causing cancer. Most people, after all, carry latent herpes simplex Type 1 viruses; yet only a small minority of the millions who suffer from cold sores at some time in their lives ever develop cancer.

Despite Black's warning, most virologists feel that their research is on the right track. They are confident that it could lead at the very least to methods for earlier detection of cancer through identification of viruses associated with specific malignancies. Spiegelman was encouraged enough about progress in virology research to make a bold prediction: that 1974 will bring the isolation and identification of two viruses that cause specific human cancers.

Doctors have been using a live-bacteria anti-tuberculosis drug called BCG to stimulate the body's natural defenses against skin and other easily reached tumors for several years. Last week a British physician reported that he has found the drug useful against acute myelogenous leukemia, a cancer of the blood-forming tissues that afflicts two out of every 100,000 adult Americans annually. Dr. Ray Powles of St. Bartholomew's Hospital in London injects into patients already treated with drugs a mixture of BCG and killed cells from other leukemic patients. The BCG alerts the patients' immune systems to the presence of both the tuberculosis bacilli and the foreign cells, stimulating the systems to destroy cancerous cells at the same time. The result has been to prolong remissions by killing off residual cancer cells. Of 21 patients who received only drugs at St. Bartholomew's since the beginning of Powles' study, only four are still alive, with an average survival time of ten months. Of 32 patients on BCG, 14 are still alive, with an average survival of 18 months.

* Similar to the strands of DNA found in the chromosomes.

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