Research eyes HPV vaccine effectiveness

Results from a new international meta-analysis study of Gardasil (Merck & Co.; Whitehouse Station, NJ), the cervical cancer vaccine, indicate the shot is nearly 100% effective against the two types of the human papillomavirus (HPV) responsible for most cases of cervical cancer.1

To perform the meta-analysis, researchers combined and analyzed data from four randomized trials that involved 20,583 women ages 15 to 26 from more than two dozen countries across Europe, North America, Latin America, and Asia. Participants were randomly assigned to receive the HPV vaccine or placebo and followed for an average of three years. Results of the analysis indicate that prophylactic administration of the vaccine was highly effective in preventing pre-malignant changes of the cervix.

3.1 million abnormal Pap smears

There are about 50 million to 60 million Pap smears performed each year in the United States, and an estimated 3.1 million are read as abnormal,2 says Kevin Ault, MD, associate professor of obstetrics and gynecology at Emory University School of Medicine and lead author of the meta-analysis. By preventing precancerous growth, not only will cervical cancer cases be reduced, but the number of abnormal Pap smears will be lessened as well, he notes.

Researchers at the Johns Hopkins University's Kimmel Cancer Center now have conclusive evidence that HPV causes some throat cancers in men and women. According to new research, oral HPV infection is the strongest risk factor for the disease, regardless of tobacco and alcohol use, and having multiple oral sex partners tops the list of sex practices that boost risk for the HPV-linked cancer.3

Study author and cancer virus expert Maura Gillison, MD, PhD, first reported the connection between HPV and specific throat cancers in 2000, which supported previous work by other investigators.4 In the current study, researchers looked at 100 men and women newly diagnosed with oropharyngeal cancer. Those who had evidence of prior HPV infection were 32 times more likely to develop the cancer, much higher than the rate increase for smokers and drinkers. Study participants who reported having more than six oral sex partners in their lifetime were 8.6 times more likely to develop the HPV-linked cancer, data show.3

HPV-linked oral cancers have been on the rise since 1973, and Gillison expects the trend to continue to a point when HPV-associated cancers will outpace those caused by tobacco and alcohol use. They currently account for 60% of oropharyngeal cancers and about one-third of all oral cavity and pharynx cancers in the United States.5

With the HPV link now established, what is the next step in research when it comes to use of HPV vaccines in prevention of oral HPV infection? Gillison says randomized, placebo controlled clinical trials are needed to evaluate whether vaccination will prevent oral HPV infection.

Check data on Cervarix

New research continues to emerge on GlaxoSmithKline's experimental HPV vaccine, Cervarix. Results of Phase III data show that at 18 months after the first of a three-dose regimen, 100% of women up to age 55 vaccinated with the candidate vaccine had antibodies present against the two most common cancer-causing HPV types: 16 and 18.6 The company awaits FDA approval of the vaccine. Its application was submitted in March 2007.

The new study looked at healthy women from Germany and Poland, ages 15 to 55. Immuno-genicity and safety were assessed at 18 months after the first dose of a three-dose vaccination regimen.

While prevalence of oncogenic HPV infection is highest in women younger than age 25, incident infection is estimated to occur in 5%-10% of women ages 25-55, state researchers in the new study. New infections decrease with age, but the proportion that persists is higher; therefore, women older than age 25 also may benefit from HPV vaccination, they conclude. [Editor's note: Access HPV vaccine patient handouts developed by the Centers for Disease Control and Prevention.]

References

  1. Ault KA; Future II Study Group. Effect of prophylactic human papillomavirus L1 virus-like-particle vaccine on risk of cervical intraepithelial neoplasia Grade 2, Grade 3, and adenocarcinoma in situ: A combined analysis of four randomised clinical trials. Lancet 2007; 369:1,861-1,868.
  2. Sirovich BE, Welch HG. The frequency of Pap smear screening in the United States. J Gen Intern Med 2004; 19:243-250.
  3. D'Souza G, Kreimer AR, Viscidi R, et al. Case-control study of human papillomavirus and oropharyngeal cancer. N Engl J Med 2007; 356:1,944-1,956.
  4. Gillison ML, Koch WM, Capone RB, et al. Evidence for a causal association between human papillomavirus and a subset of head and neck cancers. J Natl Cancer Inst 2000; 92:709-720.
  5. Johns Hopkins University. HPV Infection Linked To Throat Cancers. Press release. June 2007. Accessed at: www.hopkinskimmelcancercenter.org.
  6. Schwarz TF, Dubin G, HPV Vaccine Study Investigators for Adult Women. Human papillomavirus (HPV) 16/18 l1 AS04 virus-like particle (VLP) cervical cancer vaccine is immunogenic and well tolerated 18 months after vaccination in women up to age 55 years. J Clin Oncol 2007; 25:18s.