Vaccines to Prevent Cancer
In 2002, we saw the first reports of a highly effective vaccine against the virus that causes almost all cases of cervical cancer. And American children already are vaccinated against another virus that is a leading cause of liver cancer. Is this the cancer vaccine boom that we've all been waiting for?
By Martin Downs
Reviewed By Michael Smith
From year to year, you can count on medical science for a few golden nuggets of good news in contrast to all the reports of disaster and impending doom. Among the happiest headlines of 2002 were those announcing that a vaccine protects against the virus that causes cervical cancer. Could this be the first in a long line of cancer vaccines?
In a study that appeared in the Nov. 21 issue of The New England Journal of Medicine, nearly 1,200 women received a vaccine against a type of human papillomavirus (HPV) that causes up to 50% of cervical cancers. The same number of women received a placebo vaccine.
More than 40 women who got the placebo were infected with HPV over the following 17 months, but no infections were seen in the women that received the HPV vaccine.
But it's highly doubtful that this vaccine would ever be made available to the public because it protects against only one type of HPV. Overall, all types of HPV account for 95% of cases of cervical cancer. Any vaccine used to inoculate the public would have to protect against all types. But this study, sponsored by drugmaker Merck & Co., showed that this type of vaccine can actually prevent cervical cancer. Merck has other vaccines in the pipeline.
Study researcher Laura Koutsky, MD says, "This has been a major effort, and there have been several players."
One of the other players is Louisa Villa, MD, of the Ludwig Institute for Cancer Research in Sao Paulo, Brazil. She sits alongside Koutsky on Merck's steering committee for HPV vaccine development. In early October, Villa announced the results of a phase II clinical trial on a Merck HPV vaccine, which may actually be marketed if all goes well in the final phase of clinical testing.
These results got much less attention in the popular press than Koutsky's did -- perhaps because they were reported at an obscure conference in Paris, not in a leading American medical journal.
Villa's vaccine is designed to protect against several strains of the papillomavirus: HPV types 6, 11, 16, and 18. Types 6 and 11 cause genital warts. Together, types 16 and 18 are to blame for about 70% of all cervical cancers.
In this study, more than 1,000 women got the vaccine or a placebo three times over six months. All the women who got the vaccine became immune to the virus, whereas none of those who got the placebo did.
The vaccine could be put into use long before today's infants and toddlers grow up to become sexually active -- at which time they become vulnerable to HPV. Ian Frazer, MD, director of the University of Queensland Centre for Immunology and Cancer Research in Brisbane, Australia, told WebMD in October, "All the data to date show that this is going to be an effective vaccine."
Nevertheless, it's not a magic bullet.
Women who are already infected with HPV will still be at risk for cervical cancer. In countries like the U.S., where women routinely get Pap smears to screen for abnormal cells in the cervix, the number of deaths from cervical cancer is low (4,400 deaths in 2001, compared with 40,200 for breast cancer). But in the developing world, cervical cancer kills more women than any other cancer.
With that in mind, Frazer is working on a vaccine that not only prevents infection but also cures it. "To get a therapeutic effect is obviously very desirable in the developing world because you're not going to be able to screen people to see if they're already infected," he says.
But he says it may take more than a decade to develop this kind of vaccine.
HPV isn't the only virus that's been linked to cancer. A common virus, called Epstein-Barr, seems to play an important role in Hodgkin's disease, Burkitt's lymphoma, and nasopharyngeal cancer. Much more commonly, Epstein-Barr causes mononucleosis, or "mono," the miserable illness that strikes many of us in our teen years.
Several Epstein-Barr vaccines are being developed around the world. In October 2002, the American company MedImmune announced that their phase II vaccine trial, which was carried out in Belgium, had been a success. "We intend to take it to full clinical development," says Richard Spaete, a company executive.
Then there's the vaccine against the hepatitis B virus, which is known to cause liver cancer. The World Health Organization estimates that, globally, more than 2 billion people are infected with this virus. American children are already vaccinated against this virus in hopes that cases of hepatitis B and resulting liver cancer will become a thing of the past in years to come.
Most countries in the Western Hemisphere give the hepatitis B vaccine to infants. However, the larger part of Africa, where the virus runs rampant, still doesn't have access to the vaccine.