... amit nem Dana irt, de onnan kaptam.
Cancer Study Deemphasizes Genes' Role
By Rick Weiss
Washington Post Staff Writer
Thursday, July 13, 2000; Page A01
The vast majority of cancers are caused not by inherited defects in
people's genes, as many have come to believe in this age of genetics, but
by environmental and behavioral factors such as chemical pollutants and
unhealthy lifestyles, according to the largest cancer study ever to enter
the "nature versus nurture" debate.
"Environmental factors are more important than gene factors, and that's
important to remember, especially since everyone thinks that everything is
solved now that we have the human genome in our computers," said Paul
Lichtenstein of the Karolinska Institute in Stockholm, who led the giant
study of 89,576 twins that is reported in today's issue of the New England
Journal of Medicine.
Scientists have long recognized that environmental factors play a notable
causal role in many cancers. People from rural Asia, where breast and colon
cancers are rare, gradually grow more likely to get those diseases after
moving to the United States--the result of mostly unidentified
environmental factors. People from Japan, where stomach cancer is common,
see the risk of that disease decline after living in the United States for
All told, however, the environmental contribution to cancer has been
presumed by many experts to be as low as 50 percent. And given the recent
revolution in molecular biology, much of the modern search for the causes
of cancer has focused on genes.
To assess genetic and environmental contributions with unprecedented
precision, Lichtenstein and co-workers from Finland and Denmark used
detailed government records from their three countries to compare the
incidence of 28 different kinds of cancer in identical and nonidentical
twins. Identical twins share the same genes while nonidentical twins, on
average, are just 50 percent genetically identical--the same level of
relationship between most siblings and between parents and their offspring.
For every individual who had a cancer, the team checked whether his or her
twin ever had the same kind of cancer. The difference between the identical
and nonidentical twins gave a measure of the extent to which genes were to
blame for each kind of cancer.
On average, environmental factors caused about twice as many cancers as
inborn genetic factors. The study did not identify what exactly in the
environment put people at risk for specific types of cancer, but
researchers said cigarettes, poor diet, lack of exercise, radiation and
pollution were among the prime culprits. Prostate cancer had the strongest
genetic component, accounting for 42 percent of the risk, followed by
colorectal (35 percent) and breast cancer (27 percent).
"In the current climate, there is this sense of fatalism on the part of the
public with respect to genes. If your brother or mother has cancer, then
you feel doomed," said Robert N. Hoover of the National Cancer Institute.
However, Hoover said, the new data show that even an identical twin has
about a 90 percent chance of not getting the same cancer as his or her
affected twin. "I think that's a useful piece of information from this
study, to get away from this fatalism."
At the same time, experts noted, the few genes that so far have been
clearly linked to cancer account for just a small fraction of the 20
percent to 40 percent genetic contribution seen in the new study. That
suggests that many cancer susceptibility genes have yet to be found--and
that each probably contributes a small amount of risk to an individual, and
so may be difficult to discover.
"This raises the question of why aren't we doing more to identify avoidable
risk factors for cancer, including occupational exposures," said Devra Lee
Davis, a cancer epidemiologist at Carnegie Mellon University in Pittsburgh.
"You can't choose your parents. What you can do is control your exposures
in your environment."
But geneticists said they see a glass one-third full, not two-thirds empty.
"It's certainly true that if you're in a deterministic camp, and many
people have been migrating in that direction lately, it gives pause to see
that . . . cancer is not hardwired in the genes," said Francis Collins,
chief of the National Human Genome Research Institute. "But that should not
make people believe that the genetic approach is not going to be useful.
It's going to be incredibly useful."
Collins emphasized that all cancers are ultimately genetic in nature, since
they all are caused by cells whose genes have become disrupted, either by
inherited or acquired mutations. Thus, gene studies promise to shed
important light on the basic mechanisms of cancer.
"Even a gene that makes a small contribution," Collins said, "might be the
light bulb we've been waiting for to help us understand how cancer
(c) 2000 The Washington Post Company
Csak azert valaszolok, mert lathatolag egyikunk sem ert a visszavalthato
palackokhoz, es ez biztos jele egy kis jo parazs vitanak! -:) !
>... de ha vegignezzuk a teljes eletciklusat egy muanyag
>illetve egy uvegpalacknak, vajon melyik lesz olcsobb? Mert en nem
>tudom! Azonkivul hogy vagyunk ellatva a ketfele termek alapanyagabol?
>Mibol van tobb:homokbol vagy koolajtermekbol?
(Az utolso mondatodnak nem tudok ellenalni: a homok issza a sort, nem
tartja... Az uveg, az tenyleg homokbol van de a sor utan a homok a legolcsobb
Ha hovel akarod sterilizalni az uveget, akkor lassan kell melegitened majd
lassan hutened, vagy feledd el az egeszet es ujraolvasztasz mindent. Azt
hiszem ha csak siman raereszted a forro gozt, ugy elcsattan a sorosuveg mint
a farsangi csok. A masik gond az lehet az uveggel, hogy nagy a tomege. Egy
kilo uveget nemigen olvasztasz meg egy kilo olajjal, viszont egy kilo olajbol
tobb kilo uveggel egyenerteku palackot tudsz csinalni. (a multkor csak a
szallitasi koltseget rottam fel az uvegnek). A muanyagpalackot olyan 200C
homersekleten ujraformazod ES fertotlenited.
A kertemben hatul olyan komposztalo doboz van, ami ujradaralt zacskobol
keszult, a tereftalat palackok sokszorosan vissza lehet forgatni, hazugsag,
hogy muanyag hegynek kell elboritani a Foldet. Es trehany lustasag, ha ez
megis megtortenik! Az mas kerdes, hogy a pillanatnyi arstruktura olyan, hogy
olajbol olcsobb csinalni, mint ujrahasznositani a muanyagokat. Meg azokat is,
amelyek nagyon jol ujraforgathatok!
Ebbe az iranyba nem merek tovabb menni. Eleg szeles velemenyskalat
meglengethetnek az okok firtatasaval...