Cancer vaccine shows promise

U.S. researchers have successfully tested a vaccine against human papilloma virus, a feat many consider the first step toward the eventual prevention of most cases of cervical cancer, which is caused by the virus.

Widespread use of the vaccine, which could occur in as little as five years, could eventually result in an 85 percent reduction in the worldwide toll of 450,000 cervical cancer cases annually and 250,000 deaths. Papilloma infections could eventually fade away like polio, smallpox and diphtheria.

Another team reports today that a vaccine against herpes simplex virus 2, the primary cause of genital herpes, is 75 percent effective in women who have not previously been exposed to a herpes virus. Genital herpes afflicts one in five Americans over the age of 12.

"This is the first clinically relevant success we have had in the entire field," said Charles Ebel of the American Social Health Association, which has been leading anti-herpes campaigns. "Nothing has worked at all until now."

Some data suggest that herpes also contributes to cervical cancer, so the development of a vaccine against it would provide a double whammy. "This is the first time that this type of therapeutic intervention is available for a cancer that affects hundreds of thousands of women worldwide," said Dr. Beth Carlin of the Cedars-Sinai Medical Center in Los Angeles.

Both vaccines are now entering larger clinical trials. The herpes vaccine also could be available for clinical use in as little as five years.

Since human papilloma viruses, or HPVs, were first discovered two decades ago, researchers have identified 20 of them, five of which are involved in triggering cervical cancer. But one, HPV-16, is by far the most common, infecting an estimated 20 percent of the population and causing at least half of the cancer cases. The new vaccine is targeted specifically against HPV-16.

The vaccine is composed of virus-like particles, grown in yeast, that contain all the surface proteins of the virus but none of its genetic information. It is manufactured by Merck Research Laboratories and administered in three injections over a six-month period. Merck paid for the new study.

In the study, a team led by Dr. Laura Koutsky of the University of Washington enrolled nearly 2,400 women between the ages of 16 and 23. Half received the vaccine and half a placebo. The women were studied for an average of two years, and will be followed for an additional two.

The team reports in today's New England Journal of Medicine that 41 women in the placebo group developed HPV-16 infections during the course of the study, but none of the women receiving the vaccine. Nine cases of HPV-16-related cervical intraepithelial neoplasia — a precursor of cervical cancer — occurred among women who received the placebo, but none among those who received the vaccine.

The group is now starting trials of a vaccine that targets not only HPV-16, but also three other papilloma viruses. The four viruses account for 70 percent of cervical cancers and 90 percent of genital warts.

"The implications of having a vaccine are enormous," Koutsky said. Screening for cervical cancers with Pap smears has reduced the yearly number of deaths in the United States to about 4,100, but the tests are too expensive for most developing countries. "A vaccine could make a real impact in those countries," she said.

It could have a different kind of effect in this country, Carlin said. Many women with a curable form of cervical cancer must undergo hysterectomies, leaving them infertile. Preventing infections would eliminate most of those cases, she said.

A majority of positive Pap smears, furthermore, are associated with an HPV infection rather than cervical cancer, and each positive test requires expensive and time-consuming follow-up tests to rule out disease, Crum said.