Vaccine prevents cervical cancer in tests

Early testing shows an experimental vaccine to be 100 percent effective against the virus that causes cervical cancer, raising doctors' hopes of someday sending the lethal disease into retreat in the same way as smallpox and polio.

"It appears to be the real thing," said Dr. Christopher Crum, a pathologist at Brigham and Women's Hospital in Boston. "You're looking at some very compelling evidence that this vaccine will prevent cervical cancer."

It remains unclear how long the protection might last. Even so, researchers say a vaccine could reach the market within five years or so.

The findings were published in today's New England Journal of Medicine. The issue also carries separate research findings showing potential value in an experimental vaccine for genital herpes.

Vaccines work by teaching the body's immune defenses to recognize invading viruses and bacteria. Most types of cancer, by contrast, are blamed largely on genetic mutations and environmental factors. However, virtually all cases of cervical cancer are caused by a sexually transmitted virus -- the human papilloma virus.

A vaccine for cervical cancer is urgently being sought because the disease strikes about 450,000 women worldwide each year, killing about half. It is the leading cancer killer of women in the developing world. In the United States, where Pap tests are widely used for screening, it develops in about 15,000 women annually and kills about a third.

The new vaccine, aimed at the viral strain Type 16 responsible for about half of the cases of cervical cancer, was tested on women ages 16 to 23 at 16 sites around the country in a study led by Merck & Co. and the University of Washington. Merck developed the vaccine and funded the research. The women were watched on average for almost a year and a half.

Of 768 women who got vaccine injections, none showed Type 16 infections or precancerous tissue. Of 765 who took dummy injections, 41 came down with persistent infections, and nine developed precancerous tissue.

Inoculated women built up almost 60 times the concentration of virus-fighting antibodies seen in naturally infected women. Some researchers had suspected that the mucous membrane on the cervix would pose a barrier to such antibodies.

"For us, this is proof of principle," said Merck researcher Kathrin Jansen. "There was a lot of doubt in the beginning -- not by me, but by others -- that said it would be very difficult to prevent infection."

Making medical history

In an accompanying editorial, Crum said the vaccines developed to fight diseases like smallpox and polio are now reference points in medical history.

"If the promise implicit in the study ... is realized, we could, in our lifetime, see the gradual but progressive dismantling to the barriers to preventing cervical cancer," he said.

However, in part because cervical cancer is caused by multiple strains, it is not clear whether the disease can ever be wiped out.

Laura Koutsky, a disease specialist at the University of Washington, also cautioned: "We really only know about the short-term duration of the antibodies. Whether the antibodies persist for five years or more is not known at this point."

Dr. Douglas Lowy, a National Cancer Institute researcher, agreed that patients must be tested over longer times. But he and others agreed that a vaccine -- probably one targeted at multiple viral strains encompassing the vast share of cases -- might reach market fairly quickly.

Such a vaccine could also stop other harm done by the virus, including genital warts in both men and women and rare forms of penile, anal, vaginal and oral cancer. Researchers said the vaccine might also be taken by men to keep them from infecting their female partners.

In a separate study, the herpes vaccine, under development by GlaxoSmithKline, was about 75 percent effective in warding off genital herpes sores. But it fails to protect men, and won't work on women who have had cold sores. They are caused by a different version of the same virus.

A vaccine is already used to combat the hepatitis B virus, a sexually transmitted agent blamed for some cases of liver cancer.