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Infectious Causes of Cancer: Targets for Intervention
  1. A Morris

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    James J, ed. ($110.00.) Humana Press, 2000. ISBN 0 896 03772 X.

    The most important advance in oncology ever is the understanding that cancers (mostly) have specific causes, and that these causes may be identified, leading (potentially) to control. The causes of some cancers are infectious agents. The proposal that cancers are caused by infectious agents has had a very up and down history: today we can be certain that many cancers, including several of the very common ones, have aetiologies with infectious agents as necessary (but usually not sufficient) factors. Where a cancer has an infectious “cause” we can in principle design control strategies based on ones for infectious disease—we know how to cope with infectious diseases (mostly).

    Looking world wide we can now point at the main infectious agents involved in cancer. These are human papillomavirus (HPV), which is recognised by the World Health Organisation as a cause (and probably the primary cause) of cervical carcinoma; hepatitis B and C viruses (HBV and HCV), which certainly contribute to hepatocellular carcinoma; and Helicobacter pylori, which most certainly contributes to gastric carcinoma. These four examples probably account for a fifth or more of cancer globally. In the developed world, the proportion is rather less because the hepatitis viruses are rare. In certain areas of the world, other infectious agents are major contributors to cancer causation—for example, in Egypt, Shistosoma haematobium and bladder cancer, and in parts of the Far East, Epstein-Barr virus (EBV) and nasopharyngeal carcinoma. Perhaps dozens of other cancers, some wonderfully rare and exotic, are associated with some sort of infection.

    This present book deals with the issue of infection and cancer. It is laid out in sections according to the different class of infectious agent, with a chapter giving an overview of the biology (including molecular aspects) of the different agents (such as herpes viruses) followed by individual chapters describing the involvement of these agents with specific cancers. There is also a fascinating introductory chapter dealing with the historical aspects of the topic, reminding us of the often bizarre ideas our ancestors had about the biology of disease.

    This is a multiauthored book with the accompanying strengths and faults. The strengths are of course that the chapters are written by experts and are authoritative. The weaknesses are that the chapters are perhaps not as well integrated as they might be. My experience of editing is that it is not easy to get contributors do what you want. It is a tough editor who strikes out parts of a chapter, or worse, asks for more material or a different slant, or worst of all, says that such and such is already covered (better, at least by implication) in another chapter. The editor, if he were to do this, would end up with no chapters.

    Therefore, there is inevitably some degree of overlap, particularly in the description of the biology of infectious agents as relevant to cancer. There are other problems, particularly with the balance of the topics covered.

    I feel quite strongly that the coverage should have been weighted towards the cancers that really are quantitatively important, leaving “less important” cancers to a short summary chapter. As I indicate above, perhaps three cancers with infectious aetiology contribute to a fifth of the world burden. These should have been starred for really in depth coverage. But—for example, leiomyoma and leiomyosarcoma get 15 pages and adult T cell leukaemia gets 19 pages, whereas hepatocellular carcinoma weighs in at 17. Surely this isn't quite right.

    Likewise, one topic that I think might have been dealt with more effectively (in the space generated by reducing the treatment of the more exotic diseases) is how the different agents discussed manage to evade the immune system and so set up the chronic infection. This surely is the necessary prodrome for cancer—which after all is not an acute disease. Why does the immune system not clear these agents effectively? This is a hard question, often with no answers, but needing consideration.

    Again, another topic that deserves more space surely is the issue of intervention (the subtitle of the book). Public health measures could to a large degree reduce the incidence of infection by at least some of these agents—safe sex in the case of HPV—for example. Vaccination is another intervention route—the effective elimination of HBV in Taiwanese children is expected to reduce hugely the incidence of hepatocellular carcinoma. Eradication of the infection is a third route—for example, H pylori. What then are the prospects, say, for an HCV vaccine? And what are the practicalities of vaccinating against HBV in the third world?

    Perhaps I have sketched out a different book, and it is not fair to criticise an editor for not preparing the book I want. On the positive side, this really is a very comprehensive account of the infectious agents and the cancers they cause. It is instructive to contrast this book with that by Christopher Andrews, entitled “Viruses and Cancer”, and published some 30 years ago—not that long. Nearly all of Andrews's book dealt with animal models: the only virus associated with human cancer then was EBV—and without any certainty of whether it had a role in cancer, never mind what that role might be. Times have changed!