Abstract CN01-02: Challenges and opportunities in reducing disparities posed by human papillomavirus

The association of cervical cancer with sexual behaviour has been known for more than a century and has led to the study of different sexually transmitted infections as possible causes of the disease. Ultimately, some types of human papillomavirus (HPV), especially HPV16 and 18, have been firmly established as responsible for cervical cancer, thus paving the way for the development of a vaccine (1).

Cervical cancer has also been known for decades to have one of the strongest socio-economic gradients among all cancer sites, both between, and within countries. A large part of the socio-economic gradient currently seen is due to differences in the availability and quality of cervical cancer screening programmes. Nevertheless, socio-economic disparities in cervical cancer incidence and mortality were present well before cervical cancer screening began to spread to different parts of the world, and can still be found in countries in Asia and Africa where screening is not yet available to the vast majority of the population.

To elucidate the reasons for such disparities, we took advantage of two large series of studies coordinated by the International Agency for Research on Cancer (IARC) in the last two decades. The first, the IARC Multicentric Cervical Cancer Study (2, 3) included approximately 2,000 women with cervical cancer and the same number of cancer-free control women from 11 countries (Spain, Brazil, Colombia, Paraguay, Peru, India, the Philippines, Thailand, Algeria, Morocco and Mali). The second, the IARC HPV Prevalence Surveys (4, 5) is still on-going. At present, it includes complete information on population-based samples of approximately 18,000 women 15–64 years of age from 17 world areas (Poland, Spain, Argentina, Colombia, Chile, China - three areas, Korea, Mongolia, Thailand - two areas, Vietnam - two areas, Guinea and Nigeria).

The availability of validated information on HPV infection from both studies allows us, for the first time, to try to disentangle the extent to which socio-economic disparities in cervical cancer risk can be explained by variation in the frequency of HPV infection and/or by other known or possible correlates of low socio-economic level also associated with cervical cancer risk, e.g., number of sexual partners and age at first sexual intercourse, husband's extra-marital sexual relationships, parity and age at first birth, smoking habits, use of oral contraceptives and condom, and history of Pap smear.

In principle, opportunities to reduce disparities in cervical cancer have never been so good, as a highly effective vaccine against HPV has become available. Many different combinations of screening programmes (using Pap smear, visual inspection methods and steadily improving HPV tests) and immunization campaigns can be conceived according to the resource levels available in different parts of the world. A high-coverage vaccination programme can improve cervical cancer prevention even in the best-screened populations, and curb by two-thirds the cancer burden in unscreened women. The worst-case scenario would be that HPV vaccinations fail to reach these very same women, as well as, on a world scale, the populations most likely not to undergo adequate cervical cancer screening in their lifetime.