Viruses and the Cancers of Poverty

By George Johnson | July 25, 2013 8:47 pm

In an earlier post, “The Most Powerful Carcinogen is Entropy,” I included a pie chart that breaks down cancers in the United States according to their causes. The numbers almost always take people by surprise, mostly because of the very small percentage of cases attributed to synthetic chemicals in the environment. But it is also striking that relatively few cancers, at least in the developed world, are caused by viruses.

They seem like such likely culprits. Here is how I describe them in The Cancer Chronicles:

Existing on the boundary between chemistry and life, viruses are packets of information— streamlined sequences of DNA or RNA wrapped in a protective sheath. They are wandering genomes so simple that some consist of only three genes. Like the handmade Internet viruses they later inspired, they infiltrate their hosts (the biological computers called cells) and commandeer the internal machinery. There the invader’s genes are dutifully duplicated and repackaged again and again, the viral copies spreading to other cells where they robotically carry out the same routine—life itself stripped of its capacity to do anything except reproduce.

Since cancer is a disease of genes gone mad, it is natural to suspect that viruses would be a primary cause of cancer. But they appear to be involved in only a few varieties. The most prominent, by far, are liver and cervical cancer, and the problem is especially fierce in the poorer parts of the world, which account for about 80 percent of all cases.

Overcrowding and poor sanitation, intravenous drug use, unprotected sex — all of these are vectors of infection. The lack of medical care — especially early screening– adds another layer to the problem. While in the U.S. and other wealthy countries viruses appear to be involved in about 5 percent of all cancers, in some countries the number can be as high as 20 percent. (The worldwide average is about 13 percent.)

These maps, from the World Health Organization, illustrate the divide between rich and poor. The darker the red, the higher the cancer incidence.

Incidence of cervical cancer

Incidence of liver cancer in men

Incidence of liver cancer in women

The most distressing part of the story is that so many of these cancers are preventable.

The main cause of cervical cancer is human papilloma virus. The widespread use of pap smears has beaten back the disease in the richer countries. Abnormal, “dysplasic” cells can be identified in the gynecologist’s office and removed before they mutate further. The HPV vaccine is set to deliver the final blow.

Liver cancer is a trickier matter. A primary factor is infection by hepatitis B and C. Those can be targeted through public health programs, and there is a vaccination for hepatitis B. But early detection of the cancer itself is highly unlikely. By the time liver cancer manifests itself, it is usually too late. Another complicating factor — a huge one — is alcoholism. The scarring of liver tissue from cirrhosis and the invasion of hepatitis viruses is an especially deadly combination. Aflatoxin, which is produced by Aspergillus molds, is another important factor.

Of the hundreds of kinds of cancers, six are responsible for killing the most people worldwide. The top one is lung cancer caused by cigarettes. Like cervical and liver cancer it is also preventable. That leaves stomach cancer, colorectal cancer, and breast cancer. The latter two might be called cancers of affluence, for they tend to be most prominent in the wealthier parts of the world. But that is another story.

 

For a preview of The Cancer Chronicles, including the table of contents and index, please see the book’s website.

@byGeorgeJohnson

  • Lisa Petrison

    There’s not one word in this article about aflatoxin, even though it is well-established in the literature with regard to its role in liver cancer. Apparently it is related to HIV/AIDS too: a new paper (link below) suggests that it causes the virus to proliferate in newly diagnosed patients, and a previous study from the same group of researchers suggested that HIV+ people had much higher levels of the toxin than matched HIV- people. Discover is really missing the boat by neglecting to cover this new development, and it’s even more peculiar that you wouldn’t bring the toxins up in this blog in liver cancer, when there is a voluminous literature about their role in it.

    Then again, it’s harder to blame people for getting sick from eating moldy grain than for getting sick from having sex or drinking alcohol. If the sufferers are blameless, then maybe we would be obliged to do something to help fix the problem — especially since a lot of the moldy grain is likely coming from the U.S.

    http://www.nytimes.com/2013/07/23/health/mold-toxins-tied-to-aids-epidemic.html?_r=3&

    • http://talaya.net/ George Johnson

      Thank you for your comment. I hadn’t meant to leave out aflatoxin as a factor for liver cancer. I’ve now included a mention of it and hope to write more about it in the future.

  • Buddy199

    The most distressing part of the story is that so many of these cancers are preventable.
    —————
    Actually, that’s the good news. We now know there are simple steps that can be taken to reduce our individual risk at least.

  • http://blogs.discovermagazine.com Carol Thompson

    That’s the story according to the charlatans who use defective studies that fail to identify many cases of infection, such as liver cancer studies that ignore occult HBV (absence of circulating HBsAg in individuals positive for serum or tissue HBV DNA, irrespective of other HBV serological markers) and HCV. Their stooge at the National Cancer Institute, Welzel, pretends that hepatitis viruses are involved in less than 30% of liver cancers in the US, because they have an agenda to blame smoking and obesity. But a recent more reputable study found that markers of hepatitis viruses B and C were not found in only 6.2% of American cases, and about 5% overall. Alcohol and aflatoxin are not important in comparison.

    http://www.smokershistory.com/hepatiti.htm

    Stomach cancer can be caused by both a bacterium, Helicobacter pylori, and a virus, Epstein-Barr virus.

    http://www.smokershistory.com/heliquot.htm
    http://www.smokershistory.com/EBVgc.htm

    Epstein-Barr virus is also implicated in breast cancer.

    http://www.smokershistory.com/EBVother.htm#Breast_Cancer

    And international investigators have found human papillomavirus in about a quarter of lung cancers.

    http://www.smokershistory.com/hpvlungc.htm

    And there are many more examples. The claim that “relatively few cancers, at least in the developed world, are caused by viruses” is the party line of politically connected frauds, spread by their media toadies who refuse to critically examine any of their claims.

    • http://talaya.net/ George Johnson

      I encourage readers to look at the main page of the disreputable website the commenter is relying on for her information: http://www.smokershistory.com/. I’ll be writing more about cancer conspiracy theories in the future.

      • George
        • http://blogs.discovermagazine.com Carol Thompson

          That Brinton study dates from 1986!!! They didn’t even HAVE good technology to identify HPV then, and this study doesn’t even mention HPV anyhow. So, they did not (because they could not) account for earlier and/or more frequent HPV infection. As I have pointed out, the magnitude of confounding is proportional to the magnitude of the true cause, which in the case of HPV and cervical cancer is nearly infinite (it is involved in at least 99.7% of cases). The purported “adjustment” such as age at intercourse and number of partners quite simply doesn’t work.

          Cigarette smoking as a potential cause of cervical cancer: has confounding been controlled? AN Phillips, GD Smith. Int J Epidemiol 1994 Feb;23(1):42-49.

          http://www.ncbi.nlm.nih.gov/pubmed/8194922

          The authors and their correspondents are all anti-smokers, and so they have studiously kept their mouths shut about the fact that confounding hasn’t been controlled by those vaunted “adjustments.”.

          • George

            What about lung cancer? Is that caused by HPV?

          • http://blogs.discovermagazine.com Carol Thompson

            Yes, it can be caused by HPV, in about a quarter of cases. Needless to say, while the establishment admits the involvement of HPVs recurrent respiratory papillomatosis, and the occasional transformation of these to cancer has been recording a number of times, they don’t want to admit that other types could be involved in lung cancer as well.

            http://www.smokershistory.com/hpvlungc.htm

          • George

            The attempt to demonize cannabis smoking through biased science has been intense, and much less scrupulous than the investigation into tobacco (a legal drug, source of tax revenue, and no threat to the social order).
            Yet cannabis science has consistently drawn null or very weak correlations to the diseases associated with smoking (cigarettes), and even uncovered what may be useful anti-cancer pathways.
            This makes accusations of bias in tobacco science, especially in the early days, unconvincing, and insufficient to account for the massive correlations and many mechanical links between tobacco and cancers.

          • http://blogs.discovermagazine.com Carol Thompson

            The persecution of tobacco has been the most unscrupulous of all. Anti-smoking is not just by a few zealots, largely outside of medicine (such as religion or law enforcement), it’s by a powerful, politically connected, and unaccountable clique who have systematically corrupted health research. The anti-marijuana junk is just an imitation of anti-tobacco, using the same fraud of ignoring the role of infection (although sometimes with less impressive results because marijuana has many fans among the privileged classes.) This fraud is more than sufficient to account for anti-smoking claims. Those studies are mere comparisons of smokers versus non-smokers, therefore it is not necessary that all instances of a disease by caused by infection, but only that there be a differential of exposure between smokers and non-smokers. And the “mechanical links,” such as the vaunted claims by the Surgeon General, consist of ascribing the effects of infection to smoking!

            http://www.smokershistory.com/SGlies.html

            And, while in the early days the anti-smokers could hide behind the excuse of ignorance, today they CANNOT.

      • http://blogs.discovermagazine.com Carol Thompson

        Those who trot out worthless old junk from the 1980s have no business accusing other people of being “disreputable.”

      • Heimdall222

        For completeness, let’s note that the proprietor of the website is “Carol AS Thompson”.

        A question, though. Didn’t she leave out an “S”?

  • George

    In animals, if NAFLD progresses to NASH and cirrhosis, cases of hepatocellular cancer will appear. Neither viruses, alcohol, or toxins are required, just dietary models; a “diabetogenic” diet, usually high in sugar and a fat rich in linoleic acid (a highly saturated fat such as butter or coconut oil won’t work) produces fatty liver; adding 2% cholesterol, or restricting choline and methionine, or disrupting the intestinal wall to allow excessive gram -ve LPS into the bloodstream, will promote progression to NASH and cirrhosis (in human populations there is a positive association between pork and cirrhosis, a negative association with beef – pork, like beef, is rich in cholesterol, but its fat is not highly saturated, supplying at least 5x as much lineolic acid).
    Another factor is selenium status; selenium deficiency favours the survival of hepatoma cells over healthy hepatocytes. HCV sequesters selenium and HCV infected individuals will have lower selenium levels than their uninfected compatriots. China and Sub-Saharan Africa have low selenium soils. So does much of Europe and Australasia, but livestock is supplemented in those countries.
    “Adjusted odds ratios of HCC for subjects in increasing quintiles of plasma selenium were 1.00, 0.52, 0.32, 0.19, and 0.62, respectively.”
    http://ntur.lib.ntu.edu.tw/bitstream/246246/158938/1/25.pdf

  • Heimdall222

    George, good article, well-presented!

    As a side comment, conspiracy theorists are unfortunately always with us, sitting at their keyboards in their aluminum-foil hats (so the gubmint cain’t read ther minds), tapping away.

    Tap, tap, tap. Tap, tap, tap.

    Conspiracy theory, IMO, can be thought of as the product of weak, sick minds, or at least those with too much free time. Politics is usually a major component of any conspiracy theory rant, with a healthy side of nut-cult religion – all together now, let’s say **demagoguery**. (Yeah, yeah, I know that a certain poster here doesn’t know what that means, and I invite her to Google it!)

    As we are all aware, the world is flat, there’s no such thing as global warming or evolution, and the world was created less than 5000 years ago….

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Fire in the Mind

Whether a subtle new pattern shows up in an experiment on the Higgs boson, an epidemiological report about a suspected cancer cluster, or a double-blind trial purporting to demonstrate ESP, it can be maddeningly difficult to distinguish between what we see and what we think we see. "Fire in the Mind" takes a look at the big questions behind today’s science news.

About George Johnson

George Johnson writes about science for the New York Times, National Geographic Magazine, Slate, and other publications. His nine books include The Cancer Chronicles: Unlocking Medicine's Deepest Mystery (August 2013), The Ten Most Beautiful Experiments, A Shortcut Through Time, and Fire in the Mind. He is a winner of the AAAS Science Journalism Award and has twice been a finalist for the Royal Society science book prize. Co-founder and director of the Santa Fe Science Writing Workshop, he can be found on the Web at talaya.net. Twitter @byGeorgeJohnson.

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