Unlike other viruses that have a direct oncogenic effect (e.g. human papilloma virus and Epstein-Barr virus), HIV‚s oncogenic role appears to be rather limited. HIV is thought to facilitate, through the suppression of the immune system, the occurrence of several cancer types caused by other infectious agents, although not to affect per se the probability of cancer occurrence among infected individuals. In western countries, numerous studies have been conducted to identify the spectrum of such cancers, and to quantify their associations with HIV. Although these cancers are generally rare in the age groups affected by HIV and AIDS, sufficiently strong evidence has accumulated, since the beginning of the epidemic, for Kaposi‚s sarcoma, and non-Hodgkin‚s lymphomas. More recently, an increased risk for two other cancers has been ascertained, i.e., for Hodgkin‚s disease, and for leiomyosarcoma in children[1,2]. Cancers for which, in western countries, excesses have been suggested, although not demonstrated, include invasive cervical cancer (ICC), liver cancer, lung cancer, anal cancer, testicular cancer, oropharyngeal cancer, mieloma, and non-melanoma skin cancer[1,2].
Two papers published in the current issue of this journal, one by Parkin et al. and the other by Chokunonga et al., cover an important aspect of the epidemiology of AIDS-associated cancers: the African scenario. In accordance with previous work from Rwanda, South Africa, and Uganda, time trends in cancer incidence rates from the Kampala Cancer Registry Uganda (Parkin et al.) and from the Harare Cancer Registry, Zimbabwe (Chokunonga et al.) concur with the indication that the effect of the AIDS epidemic on Africa‚s cancer profile is restricted to three cancer types, namely, Kaposi‚s sarcoma, non-Hodgkin‚s lymphoma and squamous cell tumor of the conjunctiva.
Interestingly, Parkin et al. and Chokunonga et al. each offer the opportunity to broaden the debate on whether, in western countries, HIV-infected women are at a higher risk for ICC than uninfected women[1,2,6-10].
Relative risks (RR) for Kaposi‚s sarcoma, non-Hodgkin‚s lymphoma, ICC and Hodgkin‚s disease (i.e., cancers for which an infectious aetiology has been ascertained) derived from studies conducted among HIV-infected individuals in Africa, Australia, Europe and the United States are listed in Table 1. For Kaposi‚s sarcoma, non-Hodgkin‚s lymphoma and Hodgkin‚s disease, the RR were lower in Africa than in Australia, Europe, and in the United States. No increase in RR for ICC was registered in either Africa or in a study conducted in Australia. In contrast, a nearly 15-fold elevation in the RR for ICC was reported in Italy and in France[7,8]. The RR for ICC among women with HIV infection or AIDS in the United States contrast more sharply: RR was higher in the pre-AIDS period than after AIDS diagnosis  whereas, in another study, death rates for ICC were higher among HIV-infected women.
The RR estimates shown in Table 1 reflect the observation that, overall, infections account for 21% of cancers in developing countries and for 9% of cancers occurring in developed countries. As the prevalence of human papilloma virus, the infectious agent known to cause ICC, is higher in developing than in developed countries, this virus is responsible for a higher proportion of cervical cancers (91%) occurring in developing countries than that (82%) reported for developed nations. Thus, if HIV enhances the risk of ICC, this effect should be more evident in areas such as Italy which have a lower prevalence of the causal agent (i.e. human papilloma virus ) and lower disease rates.
HIV and human papilloma virus infections share the same risk factors, and a causal interpretation of HIV‚s association with the risk of ICC is rendered difficult by confounding from sexual promiscuity. However, HIV‚s contribution to the occurrence of infection-related cancers in Africa is, overall, less than in western countries. Thus, an underestimation of the increased ICC risk among HIV-infected women in western countries based on data from Africa may be misleading. Careful consideration should be made for the resulting public health implications, particularly with regard to high risk groups such as women who use intravenous drugs.
This work was supported by I.S.S. National AIDS Project, and by Ricerca Corrente 1998.
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