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Article Excerpt
Introduction
Cervical cancer is a gender-specific disease that disproportionately affects women in the lowest socioeconomic classes throughout the world. A meta-analysis of 57 studies revealed that there was an estimated 100% increased risk of invasive cervical cancer for women in low social class categories when compared with those in high social class categories; this difference reflects a lack of access to screening and treatment services. (1) Likewise, these differences also occur between developed and developing countries, translating inequity in access to inequity in the quality services.
In 2004, the 57th World Health Assembly adopted WHO's global reproductive health strategy, which identified five priority areas including "combating sexually transmitted infections"; the strategy also specifically addressed cervical cancer prevention. (2) In addition, a resolution on cancer prevention and control was adopted by WHO's Member States, and a new vision and strategy for global immunization that aims to ensure equal access to immunization for every child, adolescent and adult was endorsed during the 58th World Health Assembly in 2005. With the upcoming introduction of a vaccine to prevent human papillomavirus (HPV) infection, a comprehensive approach to preventing cervical cancer--which incorporates vaccination, screening and early treatment--opens up new opportunities for strengthening reproductive health services and building interdisciplinary links.
Cervical cancer: burden of disease
Cervical cancer remains the second most common cancer in women worldwide and the primary cause of cancer-related deaths among women in developing countries. (3) Screening programmes have successfully reduced disease rates in developed countries that support cytology-based services; these services are too complex for most developing countries to implement. More than 80% of the estimated 500 000 incident cases annually and more than 90% of the 257 000 deaths caused by cervical cancer occur in developing countries (Fig. 1). (4) This disparity is due in large part to the fact that a majority of women in these countries have never been screened for cervical cancer.
[FIGURE 1 OMITTED]
HPV infection
HPV is a sexually transmitted infection, recognized as the necessary cause of 99% of all cervical cancers. More than 100 types of HPV have been identified, including at least 13 types that may cause cervical cancer: these are termed "high-risk" types. Of these, HPV types 16 and 18 cause approximately 70% of cervical cancer worldwide. (5) There is geographical and country-specific variability; in sub-Saharan Africa and Latin America types 16 and 18 account for only 65% of invasive cancers. Other, "low-risk" types, mainly 6 and 11, cause genital warts in men and women but not cervical cancer. In most studies, the age-specific peak prevalence of HPV infection occurs among those aged < 25 years, and the peak incidence of cervical cancer occurs at around age 50. (5,6) Although 90% of all HPV infections are cleared, persistent infection in some women leads to the development of cancer 20 or 30 years later. This prolonged latent phase allows for screening of the cervix to detect precancerous abnormalities.
Cervical cancer screening: secondary prevention
Cervical cancer prevention programmes have been cytology-based, but their success depends upon having high rates of coverage of women in the right age group, implementing repeated quality-controlled screening and developing excellent recall services for treating precancerous abnormalities. In low-resource settings, the capacity to implement this complex, high-resource protocol to cover entire populations has been limited.
Alternative cost-effective screening and management options include visual inspection with acetic acid (VIA), with immediate cryotherapy of visible cervical lesions, and testing for HPV DNA; (7,8) these options also improve efficiency by limiting the steps a woman needs to take to access treatment. (9) When compared with cervical smear methods, the DNA screening test appears to be cost-effective, is more objective and less labour-intensive, and has high sensitivity and specificity. (10) Although the current DNA test is too expensive for use in developing countries, lower-cost tests are being developed.
HPV vaccines
HPV vaccines are prepared from virus-like particles produced by recombinant technology. The quadrivalent vaccine (Gardasil, Merck and Co., Whitehouse Station, NJ, USA) has recently been licensed, and a bivalent vaccine (Cervarix, GlaxoSmithKline Biologicals, Rixensart, Belgium) is in advanced stages of clinical testing. These HPV vaccines are designed to prevent infection with and disease from HPV 16 and 18; the quadrivalent vaccine also protects against low-risk genotypes 6 and 11. The vaccines are not designed to treat people who have already been infected with these genotypes. The results from phase III trials of Gardasil, show that it provides almost 100% protection against moderate and severe cervical intraepithelial neoplasia (CIN 2 and CIN 3) caused by the genotypes in the vaccine among women who have not previously been infected with these genotypes. (11) Gardasil...
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