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On 6/18/14 1:10 PM, DW via Marxism wrote:
Louis, it's quite well established how a carcinogen and a tumor relate
medically. Both modern science and medical statistics (the latter is how
they proved conclusively that tobacco is carcinogenic but now they have the
actual mechanisms involved).
That is not true whatsoever. I suggest you have a look at Robert N.
Proctor's "Cancer Wars: How Politics Shapes What We Know And Don't Know
About Cancer" that has a chapter on the problem of linking environmental
factors to cancer. I have tried to keep up with the literature ever
since I worked as a database administrator at Sloan-Kettering in the mid
1980s. When I was there, I read Samuel S. Epstein "The Politics of
Cancer", a book with a somewhat different angle than Proctor's. Both are
very good.
http://www.scientificamerican.com/article/how-many-cancers-are-caused-by-the-environment/
The old two percent estimate for environmentally induced cancers is
still commonly used – despite advances in modern cancer biology.
New areas of cancer research are focusing on the potential for
pollutants to interact with one another and with genetic factors.
Carcinogens can act by damaging DNA, disrupting hormones, inflaming
tissues, or switching genes on or off.
Also, exposure to hormonally active agents during critical periods of
human development – particularly in the womb or during childhood – may
trigger cancer later in life. For example, the risk of breast cancer
could be influenced by exposures during puberty.
All these elements make it tricky to calculate the magnitude of
environmentally induced cancers.
Scientists now know that getting cancer is like being attacked by a
multi-headed monster: How can you really be sure which part did the most
damage?
Schettler said “we now know from cancer biology that multiple
interacting factors” are involved so it’s impossible to assign
percentages to certain causes.
“It’s really important that we understand the limits of this notion. We
have to be humbled by this and know that our estimates may be way off,”
he said.
Margaret Kripke, a professor at University of Texas' M.D. Anderson
Cancer Center and co-author of the President’s Cancer Panel report, said
the idea that cancer biologists can put a number on the environmental
component of cancer is fraught with limitations.
She uses the example of a person who is genetically predisposed to lung
cancer, but also smokes and lives in an area with high air pollution. If
this person develops cancer, it is almost always attributed to smoking
because almost 90 percent of lung cancer deaths are caused by tobacco.
But researchers can't simply dismiss the remaining 10 percent. The way
these fractions are teased apart is crucial, and important contributors
are easily overlooked by limitations in study design.
There is substantial evidence that synergism between two different
exposures can cause some cancers. Asbestos, for example, enhances the
carcinogenicity of tobacco smoke, so the rate of lung cancer was
especially high among people who smoked and also were exposed to
asbestos in their workplaces.
The major reason that it’s so difficult to pin down how many cancers are
due to environmental factors is that studies that allow epidemiologists
to link human cancers to an environmental pollutant are rare opportunities.
Scientists need a setting where they can be absolutely certain about
what and when people were exposed to something, and then be able to
follow up with the patients many years later, since cancer takes decades
to develop. Yet this is hardly ever possible, said Dr. Richard Jackson,
former director of the federal Centers for Disease Control and
Prevention’s National Center for Environmental Health.
Humans aren't lab rats; they tend to move around, so they don't know
what they were exposed to, said Jackson, who is now a UCLA professor.
Also, tracking systems for environmental exposures and chemicals are
inadequate.
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