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By the way, doctor: Should I be vaccinated against cervical cancer?

By the way, doctor

Should I be vaccinated against cervical cancer?

Q. Recently, I read about a vaccine against cancer of the cervix. Is this something I should consider?

A. You're referring to two vaccines in development as of spring 2006 for use against the human papilloma virus (HPV), a virus that causes most cases of cervical cancer. Neither is on the market yet, but they are an exciting development in science and medicine.

Of the 100 types of HPV, 30–40 of them are sexually transmitted and cause genital HPV infection. Some cause genital warts, while others trigger changes in the cells of the cervix that can progress to cervical cancer. Genital HPV is very common — 5.5 million new cases occur each year, and about 20 million men and women are thought to have active HPV infection at any given time.

HPV is spread through contact with infected genital skin or mucous membranes. The body's immune system usually eliminates the virus within months, but occasionally it persists. Women over age 30 have more trouble getting rid of it than younger women.

Routine screening with Pap smears vastly reduces the risk of an HPV infection causing cervical cancer. Because the cancer grows slowly, Pap testing can identify early changes in cervical cells, and the cells can be removed before they cause trouble. In the United States, Pap tests have dramatically reduced the rate of cervical cancer. Between 1975 and 2000 alone, the annual rate of invasive cervical cancer fell by 50%, from 14.8 cases per 100,000 women to 7.6 cases per 100,000 women.

Still, there are new cases of invasive cervical cancer every year. The American Cancer Society estimates that close to 10,500 women were diagnosed with cervical cancer in 2005 and nearly 4,000 died of it. In developing countries, where Pap test screening is not in place, cervical cancer remains a common cancer and significant cause of death.

Scientists have determined that 13 of the 30–40 sexually transmitted types of HPV are associated with cervical cancer. Two particular types, types 16 and 18, account for 70% of all cervical cancer. Two manufacturers have developed vaccines against them. Merck's vaccine, called Gardasil, targets not only types 16 and 18 but also types 6 and 11, which are major causes of genital warts. GlaxoSmithKline's version, Cervarix, targets only types 16 and 18.

Merck is further along in testing its vaccine. In the FUTURE II trial, more than 12,000 women ages 16–23 were randomly assigned to receive three doses of Gardasil or placebo over six months. During the 18 months that followed, more than 99% of vaccinated women produced antibodies to the targeted HPV types. And none of the vaccinated women developed HPV infection, compared to 21 who did so in the placebo group. The vaccine was found to be very safe: Side effects were the same in both the vaccinated and placebo groups. The FDA is expected to make its decision by early June 2006.

The possibility of a vaccine that would protect against 70% of cervical cancer–causing HPV has special significance for developing countries, which lack the infrastructure to support routine Pap testing. However, questions remain. We don't know how long the vaccine is protective. To find out, Merck will keep track of a group of FUTURE II participants for several years. Also, the vaccine doesn't protect against all cervical cancer–causing HPV. Those who received it would still be vulnerable to other types, which cause 30% of all cases of cervical cancer. That's why even vaccinated women would need to continue to be screened. Critics are concerned that introduction of the vaccine will induce women to skip routine Pap smears.

Young women and women with several sexual partners are most at risk for HPV infection. Target groups for the vaccine are 13-year-old girls (to protect them before they start sexual activity) and possibly older women who are newly sexually active. It remains to be seen whether parents of early adolescent girls will be willing to have their daughters vaccinated.

Even if the vaccine is widely accepted, it may be decades before we see a vaccine-related reduction in cervical cancer, because it takes so long for cancer to grow following infection. But the prospect of having a vaccine that might eliminate most HPV-related cervical cancer has major implications for the future of cancer prevention in women worldwide.

— Celeste Robb-Nicholson, M.D. Editor in Chief, Harvard Women's Health Watch

Last updated:	September 05, 2008