February 23, 2007

Cervical cancer and the HPV vaccine

By Phuong H Nguyen MD, FACOG
Chief of Gynecology
Santa Clara Valley Medical Center
Special to the Times

Cervical cancer is cancer of the lower part of the womb. In 2006, the American Cancer Society estimated that about 9,700 women were diagnosed with cervical cancer and 3,700 died from it.

Cervical cancer incidence is higher among certain ethnic groups and geographic regions. For instance, African American and Vietnamese American women have a higher rate than the general population. Hispanic women living along the US-Mexico border areas also have higher rates of cervical cancer.

Virtually all cervical cancers are causally related to human papillomaviruses (HPV) infections. These viruses are very common, primarily transmitted sexually and have the ability to infect epithelial cells. There are over 100 known strands of HPV. Of these, 40 HPV types can infect the genital areas.

In the United States, it is estimated that 20 Million people (15 percent of the population) are currently infected with HPV as detected by HPV DNA. Of these, over 6 million people are infected with genital HPV and about 1.4 million people have genital warts.

HPV 6 and 11 are responsible for 90 percent of anogenital warts. Some HPV types are carcinogenic (cause cancer). These HPV cause the epithelial cells to change in ways that, if left untreated, can progress from the precancerous states (CIN2/3) to cervical cancer over time. HPV 16 and 18 cause about 70 percent of all cervical cancers.

Until recently, Pap smear screening with or without high risk HPV typing is the mainstay of cervical cancer prevention. Since the implementation of population-based organized and opportunistic Pap smear screening in 1949, the incidence of cervical cancer and its morbidity in the United States have decreased by 70 percent. This is a significant accomplishment.

However, Pap smear screening alone can not eradicate cervical cancer. One reason is that the Pap test has limited sensitivity. This means that even with adequate collection of the exfoliated cervical epithelial cells, the Pap test can miss some lesions. Secondly, women with abnormal pap results do not always follow up as recommended. Thirdly, many women do not obtain pap screening. It is estimated that one half of all women with cervical cancer have never been screened and 10 percent have not had a pap within five years prior to the diagnosis and treatment of cervical cancer.

In June of 2006, the Food and Drug Administration (FDA) approved the use of the quadrivalent HPV vaccine (Gardasil) for the prevention of infection with HPV 6, 11, 16 and 18 in girls and women between the ages of 9 to 26 years. This came about after studies, which showed the vaccine is 95-100 percent effective in preventing the acquisition of the above mentioned HPV strands. In addition, the vaccine’s side effect profile is excellent with the most common side effects being those related to injection site, i.e. erythema, pain and swelling. Of note, the vaccine does not contain mercury or thimerosal. A second vaccine, Cervarix, is anticipated to be available in the U.S. in the near future.

Because the primary mode of HPV infection transmission (how it passes from one person to the next) is sexual contact, the best time to give the vaccine is before the onset of sexual activity. However, women who are sexually active may still benefit. This is because the majority of women in this age group have not been exposed to all four strands. The vaccine is give as a series of three shots. The cost is about $360 for the series.

HPV vaccine does not treat already established infection and does not protect against other HPV strands. Because of this, women should still continue with Pap smear screening. Efficacy trials of HPV vaccine in young men are ongoing and results are expected later this year.

For more information on HPV, HPV vaccine and cervical cancer please speak to your pediatrician, primary physician, gynecologist or go to www.cdc.gov, http://caonline.amcancersoc.org/cgi/content/full/57/1/7.