The need for preventive drugs and vaccines in global cancer

Factors decrease the risk especially adequate intake

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factors decrease the risk, especially adequate intake of fruit and vegetables (IARC, 2003). One rando- mized intervention trial carried out in Colombia showed that eradication of the H. pylori infection resulted in a statistically significantly increased rate of regression of precursor lesions in stomach (Correa et al. , 2000). This trial was also able to demonstrate that dietary supplementation for six years with either ascorbic acid or beta-carotene in subjects with atrophic (non-metaplastic) gastritis also increased the risk of regression of lesions. Immunization for cancer prevention Hepatitis B vaccination can be expected to prevent liver cancer in high risk countries with a high prevalence of infection. However, infants need to be vaccinated, and a major impact on liver cancer incidence cannot be expected for about 40 years, although there are other, more immediate non- cancer benefits from vaccination. Hepatitis B im- munization in children has already reduced the incidence of infection in China, Korea and West Africa. IARC, in collaboration with the Govern- ment of the Republic of Gambia and the labora- tories of the United Kingdom Medical Research Council (MRC) has conducted a large-scale hepa- titis intervention study. The first phase of the study involved the introduction over a five-year period of a vaccine against hepatitis B virus (HBV) into the expanded programme of vaccination of the Gam- bia, so that about one-half of the children born between the years 1986 and 1990 received the vaccine, while an equal number did not. The vaccine proved to have 95% efficiency in protecting against chronic HBV infection. The cancer inci- dence among vaccinated and control individuals is now being followed (IARC, 2001). Cancer of the cervix, the most common female cancer in parts of India and Latin America, is clearly associated with certain subtypes of human papillomaviruses (HPVs). Prophylactic vaccines may soon become available against oncogenic papillomaviruses. Of the more than 30 types of HPV known to infect human genitalia, HPV type 16 (HPV-16) is most commonly linked with cancer, since it is present in 50% of cervical cancers and high-grade cervical intraepithelial neoplasias (Bosch et al. , 1995). A double blind, randomized clinical trial has shown that HPV-16 L1 virus-like particle vaccine reduced the incidence of both HPV- 16 infection and HPV-16-related cervical intrae- pithelial neoplasia (Koutsky et al. , 2002). If the promise implicit in the study by Koutsky and coworkers is realized, we could in our lifetime see a gradual but progressive dismantling of barriers to preventing cervical cancer. However, we have to realise that even if a vaccine for HPV-16 and HPV- 18 became widely available soon, it would take at least 30 years from vaccination before there was a clear effect on invasive cancer of the cervix. In Preventive drugs and vaccines in cancer control H Vainio 86
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contrast, screening and/or treatment, if effective, can have a rapid impact. For some time, the incidence and mortality associated with cancer of the cervix has been falling in developed countries.
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