Prevention of Cervical Cancer

Summary Type: Prevention
Summary Audience: Health professionals
Summary Language: English
Summary Description: Expert-reviewed information summary about factors that may increase the risk of developing cervical cancer and about approaches that may help in the prevention of this disease.

Prevention of Cervical Cancer

Summary of Evidence

Note: Separate PDQ summaries on Screening for Cervical Cancer and Cervical Cancer Treatment are also available.

Avoidance of Human Papillomavirus Infection

Based on solid evidence, the following measures are effective to avoid human papillomavirus (HPV) infection, and thus cervical cancer:

Abstinence from sexual activity

Description of the Evidence
• Study Design : Evidence obtained from cohort and case-control studies.
• Internal Validity : Good.
• Consistency : Good.
• Magnitude of Effects on Health Outcomes : Abstinence prevents HPV infection.
• External Validity : Good.

Barrier protection and/or spermicidal gel during sexual intercourse

Description of the Evidence
• Study Design : Evidence obtained from cohort and case-control studies.
• Internal Validity : Good.
• Consistency : Good.
• Magnitude of Effects on Health Outcomes : Total use of barrier protection decreases cancer incidence, relative risk of 0.4 (95% confidence interval [CI], 0.2–0.9)

Based on fair evidence, vaccination against HPV-16/HPV-18 is effective to avoid HPV infection, and thus cervical cancer.

Description of the Evidence
• Study Design : Evidence obtained from randomized controlled trials.
• Internal Validity : Good.
• Consistency : Not applicable.
• Magnitude of Effects on Health Outcomes : Vaccination against HPV-16 and HPV-18 reduces incident and persistent infections with efficacy of 91.6% (95% CI, 64.5–98.0) and 100% (45–100), respectively. Duration of efficacy is not yet known.
• External Validity : Good.

Screening via Gynecologic Examinations and Cytologic Screening

Based on solid evidence, screening via regular gynecologic examinations and cytologic test (Papanicolaou smear) with treatment of precancerous abnormalities decreases the incidence and mortality of cervical cancer.

Description of the Evidence
• Study Design : Evidence obtained from cohort or case-control studies.
• Internal Validity : Good.
• Consistency : Good.
• Magnitude of Effects on Health Outcomes : Estimates from population studies suggest that screening may decrease cancer incidence and mortality by more than 80%.
• External Validity : Good.

Cigarette Smoke

Based on solid evidence, cigarette smoking, both active and passive, increases the risk of cervical cancer.

Description of the Evidence
• Study Design : Evidence obtained from cohort or case-control studies.
• Internal Validity : Good.
• Consistency : Good.
• Magnitude of Effects on Health Outcomes : Among HPV-infected women, current and former smokers have approximately two to three times the incidence of high-grade cervical intraepithelial neoplasia or invasive cancer. Passive smoking is also associated with increased risk, but to a lesser extent.
• External Validity : Good.

Reproductive Behavior

High parity

Based on solid evidence, high parity is associated with increased risk of cervical cancer.

Description of the Evidence
• Study Design : Evidence obtained from cohort or case-control studies.
• Internal Validity : Good.
• Consistency : Good.
• Magnitude of Effects on Health Outcomes : Among HPV-infected women, women who have had seven or more full-term pregnancies have approximately four times the risk of squamous cell cancer compared with nulliparous women and two to three times the risk of women who have had one or two full-term pregnancies.^1,
• External Validity : Good.

Long-term use of oral contraceptives

Based on solid evidence, long-term use of oral contraceptives is associated with increased risk of cervical cancer.

Description of the Evidence
• Study Design : Evidence obtained from cohort or case-control studies.
• Internal Validity : Good.
• Consistency : Good.
• Magnitude of Effects on Health Outcomes : Among HPV-infected women, women who used oral contraceptives for 5 to 9 years have approximately three times the incidence of invasive cancer, and those who used them for 10 years or longer have approximately four times the risk.^2,
• External Validity : Good.

¹ Muñoz N, Franceschi S, Bosetti C, et al.: Role of parity and human papillomavirus in cervical cancer: the IARC multicentric case-control study. Lancet 359 (9312): 1093-101, 2002.

² Moreno V, Bosch FX, Muñoz N, et al.: Effect of oral contraceptives on risk of cervical cancer in women with human papillomavirus infection: the IARC multicentric case-control study. Lancet 359 (9312): 1085-92, 2002.

Significance

Incidence and Mortality

An estimated 11,150 new cervical cancers and 3,670 cervical cancer deaths will occur in the United States in 2007.¹ An additional 1,250,000 women will be diagnosed with precancers annually by cytology using the Pap smear. A continuum of pathologic changes may be diagnosed, ranging from atypical squamous cells of undetermined significance to low-grade squamous intraepithelial lesions (LSIL) to high-grade squamous intraepithelial lesions (HSIL) to invasive cancer. The precancerous conditions LSIL and HSIL are also referred to as cervical intraepithelial neoplasia (CIN) 1, 2, and 3. Lesions can regress, persist, or progress to an invasive malignancy, with LSIL (CIN 1) more likely to regress spontaneously and HSIL (CIN 2/CIN 3) more likely to persist or progress. The average time for progression of CIN 3 to invasive cancer has been estimated to be 10 to 15 years.^2,

The incidence of cervical cancer has decreased dramatically with the advent and widespread adoption of screening via gynecological examinations and Pap smears (refer to the PDQ summary on Screening for Cervical Cancer for more information). Regular screening, however, is associated with large numbers of diagnostic procedures to evaluate abnormal tests, and the treatment of low-grade lesions may adversely affect subsequent fertility and pregnancy. Prevention of cancer may be more efficient, with fewer adverse consequences.

Nearly all cases of cervical cancer are associated with human papillomavirus (HPV) infection,^3,4 which is transmitted during sexual activity. Therefore, cervical cancer is seen more frequently in women with sexual activity at an early age and with multiple partners. Barrier contraception and/or spermicidal gels may offer some protection (refer to the Human Papillomavirus section).

Cigarette smoking or exposure to environmental smoke is also associated with increased risk among HPV-infected women,⁵ suggesting that components of tobacco are promoters of abnormal growth of viral-infected cells.

¹ American Cancer Society.: Cancer Facts and Figures 2007. Atlanta, Ga: American Cancer Society, 2007. Also available online. Last accessed March 5, 2007.

² Holowaty P, Miller AB, Rohan T, et al.: Natural history of dysplasia of the uterine cervix. J Natl Cancer Inst 91 (3): 252-8, 1999.

³ zur Hausen H, de Villiers EM: Human papillomaviruses. Annu Rev Microbiol 48: 427-47, 1994.

⁴ Schiffman MH, Bauer HM, Hoover RN, et al.: Epidemiologic evidence showing that human papillomavirus infection causes most cervical intraepithelial neoplasia. J Natl Cancer Inst 85 (12): 958-64, 1993.

⁵ Ho GY, Kadish AS, Burk RD, et al.: HPV 16 and cigarette smoking as risk factors for high-grade cervical intra-epithelial neoplasia. Int J Cancer 78 (3): 281-5, 1998.

Evidence of Benefit

Human Papillomavirus

Epidemiologic studies to evaluate risk factors for the development of squamous intraepithelial lesions (SIL) and cervical malignancy demonstrate conclusively a sexual mode of transmission of a carcinogen.¹ It is now widely accepted that human papillomavirus (HPV) is the primary etiologic infectious agent.^2,3,4 Other sexually transmitted factors, including herpes simplex virus 2, may play a cocausative role.¹ The finding of HPV viral DNA integrated in most cellular genomes of invasive cervical carcinomas supports epidemiologic data linking this agent to cervical cancer;⁵ however, direct causation has not been demonstrated. More than 80 distinct types of HPV have been identified, approximately 30 of which infect the human genital tract. HPV types 16 and 18 are most often associated with invasive disease. Characterization of carcinogenic risk associated with HPV types is an important step in the process of developing a combination HPV vaccine for the prevention of cervical neoplasia. In a population-based study of HPV infection and cervical neoplasia in Costa Rica, 80% of high-grade squamous intraepithelial lesions (HSIL) and invasive lesions were associated with HPV infection by 1 or more of 13 cancer-associated types.⁶ In this study, the risk of about half of HSIL and invasive cervical cancer was attributable to HPV-16. HPV-18 was associated with 15% of invasive disease but only 5% of HSIL, suggesting that HPV-18 may have a role in more aggressive cases of cervical malignancy.

Barrier methods of contraception are associated with a reduced incidence of SIL presumptively secondary to protection from sexually transmitted disease.^7,8 The effectiveness of condom use for the prevention of HPV infections has been evaluated in a prospective study of women aged 18 to 22 years who were virgins.⁹ The number of vulvovaginal HPV infections was reduced with consistent condom use; HPV infection rate was 37.8 infections per 100 patient-years among women whose partners used condoms 100% of the time in the 8 months before testing, compared with 89.3 infections per 100 patient-years among women whose partners used condoms less than 5% of the time (P trend = .005). No cervical squamous intraepithelial lesions were detected among women reporting 100% condom use by their partner.⁹

Given the etiologic role of HPV in the pathogenesis of cervical neoplasia, vaccines to immunize against HPV infection would offer a primary prevention strategy for cervical cancer. Vaccines using HPV late protein (L1 and L2) constructs to induce antibody-mediated immunity are in clinical trials.^10,

Vaccine to prevent HPV infection

Persistent infection with oncogenic types of HPV such as HPV-16 and HPV-18 is associated with the development of cervical cancer.¹¹ A vaccine to prevent HPV infection with oncogenic-type viruses has the potential to reduce the incidence of cervical cancer. A vaccine against HPV-16 using empty-viral capsids called virus-like particles was developed and tested for efficacy in preventing persistent infection with HPV-16.

A multicenter, double-blind, placebo-controlled trial enrolled 2,391 women aged 16 to 23 years and randomly assigned them to receive either 40 µg of HPV-16 L1 virus-like particle (VLP) vaccine or placebo on day 1, at 2 months, and at 6 months. Pap tests and genital samples for HPV-16 DNA were obtained on day 1, at 7 months, and every 6 months for 48 months. Colposcopy and cervical biopsies were obtained when clinically indicated at study exit. Serum HPV-16 antibody titers were obtained at study entry, at 7 months, and then every 6 months. A total of 1,505 women (755 receiving vaccine and 750 receiving placebo) completed all three vaccinations and had follow-up after month 7. After immunization, HPV titers peaked at month 7, declined through month 18, and then stabilized in months 30 through 48. There were no cases of cervical intraepithelial neoplasia (CIN) in the vaccine-treated women, but there were 12 cases in the placebo group (6 CIN 2 and 6 CIN 3). HPV-16 infection that persisted for at least 4 months was seen in 7 vaccine-treated women versus 111 placebo-treated women.^12,

An international, double-blind, placebo-controlled trial of a bivalent HPV-16/HPV-18 virus-like particle vaccine was performed in 1,113 women aged 15 to 25 years.¹³ Women received either vaccine or placebo at 0, 1, and 6 months and were assessed by cervical cytology and self-obtained cervicovaginal samples for up to 27 months. Follow-up analysis of 776 women showed that vaccinated women had stable serum antibody titers at 4.5 years and continued protection against HPV-16/HPV-18 infection. Incident infections decreased from 28 of 277 control women to 1 of 310 vaccinated women, a decline of 96.9% (confidence interval [CI], 81.3%–99.9%). Persistent infections according to 12-month definition decreased from 10 of 340 control women to 0 of 357 vaccinated women, a decline of 100% (CI, 57.0%–100%). CIN 1+ and CIN 2+ associated with HPV-16/HPV-18 were reduced from 13 of 470 control women to 0 of 481 vaccinated women. Incident infections with HPV-45 and HPV-31 were reduced by 94% and 54%, respectively. Adverse events, serious adverse events, and new-onset chronic disease were similar in vaccinated and placebo-treated women.

The type-specific vaccines, if successful in preventing invasive cancer, will offer protection for only a subset of cases, the proportion of which will vary worldwide.¹⁴ Using data from a multicenter case-control study conducted in 25 countries, it was estimated that a vaccine containing the seven most common HPV types could prevent 87% of cervical cancers worldwide. A vaccine with HPV-16 and HPV-18 types, the two most common strains, would prevent 71% of cervical cancers worldwide.^14,

Cigarette Smoking

Cigarette smoking by women is associated with an increased risk for squamous cell carcinoma.^1,15,16 This risk increases with longer duration and intensity of smoking and may be present with exposure to environmental tobacco smoke, being as high as four times that of women who are nonsmokers and are not exposed to environmental smoking.¹ Case-control studies of women infected with HPV have examined the effect of various types and levels of tobacco exposure and found similar results.^16,17,

Reproductive Behavior

High parity has long been recognized as a risk factor for cervical cancer, but the relation of parity to HPV infection was uncertain. A meta-analysis of eight case-control studies on invasive cervical cancer and two studies of in situ cancer was performed, using only those women who were positive for HPV DNA by polymerase chain reaction (PCR)-based assays. The study included 1,465 women with squamous cell invasive cancers, 211 with in situ cancers, 124 with adenocarcinomas or adenosquamous invasive cancers, and 255 controls. Squamous cell cancer risk was associated with the number of full-term pregnancies. The odds ratio (OR) for women with seven or more full-term pregnancies was 3.8 (95% CI, 2.7–5.5) compared with nulliparous women. The OR for women with seven or more full-term pregnancies was 2.3 (1.6–3.2) compared with women with one or two full-term pregnancies.^18,

Long-term use of oral contraceptives has also been known to be associated with cervical cancer, but its relation to HPV infection was also uncertain. A pooled analysis of HPV-positive women from the studies described above was undertaken. Compared to women who have never used oral contraceptives, those who have used them for fewer than 5 years did not have an increased risk of cervical cancer (OR = 0.73; 95% CI, 0.52–1.03). The OR for women who used oral contraceptives for 5 to 9 years was 2.82 (1.46–5.42), and for 10 or more years the OR was 4.03 (2.09–8.02).^19,

Dietary Factors

Multiple case-control studies show an association between intake of some micronutrients and lower risk of cervical cancer, but results are conflicting and difficult to control for other risk factors. Two randomized trials of oral folate as a chemopreventive agent have shown no protective effect.

¹ Brinton LA: Epidemiology of cervical cancer--overview. IARC Sci Publ (119): 3-23, 1992.

² Schiffman MH, Bauer HM, Hoover RN, et al.: Epidemiologic evidence showing that human papillomavirus infection causes most cervical intraepithelial neoplasia. J Natl Cancer Inst 85 (12): 958-64, 1993.

³ Ley C, Bauer HM, Reingold A, et al.: Determinants of genital human papillomavirus infection in young women. J Natl Cancer Inst 83 (14): 997-1003, 1991.

⁴ Muñoz N, Bosch FX, de Sanjosé S, et al.: The causal link between human papillomavirus and invasive cervical cancer: a population-based case-control study in Colombia and Spain. Int J Cancer 52 (5): 743-9, 1992.

⁵ Reeves WC, Rawls WE, Brinton LA: Epidemiology of genital papillomaviruses and cervical cancer. Rev Infect Dis 11 (3): 426-39, 1989 May-Jun.

⁶ Herrero R, Hildesheim A, Bratti C, et al.: Population-based study of human papillomavirus infection and cervical neoplasia in rural Costa Rica. J Natl Cancer Inst 92 (6): 464-74, 2000.

⁷ Parazzini F, Negri E, La Vecchia C, et al.: Barrier methods of contraception and the risk of cervical neoplasia. Contraception 40 (5): 519-30, 1989.

⁸ Hildesheim A, Brinton LA, Mallin K, et al.: Barrier and spermicidal contraceptive methods and risk of invasive cervical cancer. Epidemiology 1 (4): 266-72, 1990.

⁹ Winer RL, Hughes JP, Feng Q, et al.: Condom use and the risk of genital human papillomavirus infection in young women. N Engl J Med 354 (25): 2645-54, 2006.

¹⁰ Schiller JT: Papillomavirus-like particle vaccines for cervical cancer. Mol Med Today 5 (5): 209-15, 1999.

¹¹ Wallin KL, Wiklund F, Angström T, et al.: Type-specific persistence of human papillomavirus DNA before the development of invasive cervical cancer. N Engl J Med 341 (22): 1633-8, 1999.

¹² Mao C, Koutsky LA, Ault KA, et al.: Efficacy of human papillomavirus-16 vaccine to prevent cervical intraepithelial neoplasia: a randomized controlled trial. Obstet Gynecol 107 (1): 18-27, 2006.

¹³ Harper DM, Franco EL, Wheeler CM, et al.: Sustained efficacy up to 4.5 years of a bivalent L1 virus-like particle vaccine against human papillomavirus types 16 and 18: follow-up from a randomised control trial. Lancet 367 (9518): 1247-55, 2006.

¹⁴ Muñoz N, Bosch FX, Castellsagué X, et al.: Against which human papillomavirus types shall we vaccinate and screen? The international perspective. Int J Cancer 111 (2): 278-85, 2004.

¹⁵ Hellberg D, Nilsson S, Haley NJ, et al.: Smoking and cervical intraepithelial neoplasia: nicotine and cotinine in serum and cervical mucus in smokers and nonsmokers. Am J Obstet Gynecol 158 (4): 910-3, 1988.

¹⁶ Brock KE, MacLennan R, Brinton LA, et al.: Smoking and infectious agents and risk of in situ cervical cancer in Sydney, Australia. Cancer Res 49 (17): 4925-8, 1989.

¹⁷ Ho GY, Kadish AS, Burk RD, et al.: HPV 16 and cigarette smoking as risk factors for high-grade cervical intra-epithelial neoplasia. Int J Cancer 78 (3): 281-5, 1998.

¹⁸ Muñoz N, Franceschi S, Bosetti C, et al.: Role of parity and human papillomavirus in cervical cancer: the IARC multicentric case-control study. Lancet 359 (9312): 1093-101, 2002.

¹⁹ Moreno V, Bosch FX, Muñoz N, et al.: Effect of oral contraceptives on risk of cervical cancer in women with human papillomavirus infection: the IARC multicentric case-control study. Lancet 359 (9312): 1085-92, 2002.

Changes To This Summary (02/20/2007)

The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Significance

Updated text on incidence and mortality estimates for 2007 (cited American Cancer Society as reference 1).

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