Download How often these days do you read that genes cause cancer

Genetic Seeds of Disease: How to Beat the Odds
BY: T. COLIN CAMPBELL, PHD
How often these days do you read that genes cause cancer? Probably nothing in
biomedical science deserves more attention. In my view, it even needs attention in
nutrition newsletters. Why? Because there's a peculiar line of reasoning going around
that goes something like this: If genes are primarily responsible for determining when
and what kinds of cancer we get, then what difference does it make what we eat?
Essentially, this is a very fatalistic view. Further, if this notion about genes is accepted
as being valid, then many may be tempted to simply trade in "bad" genes for "good"
genes. Regrettably, this is an idea that is very much alive in science and kicking up
considerable funding support. Rather than succumbing fatalistically to gene research
reports or trading our genes haphazardly, let's start to think more seriously about
preventing cancer, quite literally, by getting at its "root."
Where is the Money Going?
I've previously commented in this newsletter on some of my concerns about this
overemphasis on gene research (see August 1995 issue). While some of the new gene
discoveries may provide hopeful opportunities, many are clearly harmfulespecially
when people are not properly informed. Tragically, some people have become so
distraught after finding out that they or their loved ones have a particular bad gene, that
they then take unconscionable actionI've been called twice by mothers seeking advice
on possible mastectomies for their daughters.
Why do NIH and similar funding agencies provide far more research funding for
investigations on the genetic control of disease rather than for the nutritional control of
disease? Whose purpose is being served here? Consider this: Improper diets, when
compared to genetic backgrounds, are responsible for perhaps 30–40 times more
cancers (at least), yet genetic research, according to my estimate, gets 30–40 times
more funds.
On the more hopeful side, however, I would say this. If genes only indicate potential,
not certainty for disease, then knowledge of troublesome genes may motivate people to
be more careful about their dietary and lifestyle habits.
New Study Reveals Major Research Flaws
My reason for returning to this subject yet again in this newsletter is a very important
study published this past spring. The findings of this study make a particularly
compelling point that genes matter little, practically speaking, in the causation of
cancer. I can hardly imagine a study being more devastating to the idea that genes are
responsible for cancer risk. The study I have in mind was undertaken by scientists
within the National Cancer Institute (NCI) of the NIH. The study group was headed by
a very prominent and experienced senior investigator, Dr. Robert Hoover.
The investigators asked a very simple question about whether identical twins were
more likely to get cancers than were other sibling pairs. You see, identical twins have
essentially the same genes, thus they should get the same cancers if their genes are the
primary cause. According to this reasoning, if one member of the twin pair gets a
specific cancer, then the second member, who carries the same genes, should also get
it.
The extent to which the same cancers occurred for both members of an identical twin
pair (same genes) was compared with the extent to which both members of a nonidentical twin pair got the same cancer. The genes of non-identical twin pairs are no
more alike than any other pair of siblings.
The findings from this study are unusually revealing. First, this study was the largest of
its kind ever undertaken. Cancer deaths among 5,690 identical twin pairs were
compared with cancer deaths among 7,248 non-identical twin pairs. Second, careful
attention was given to include the details of record keeping so that only those records
with verifiable information would be used in the analysis. It was, in my view, a welldesigned and well-executed study.
Briefly, without getting into all the detailed findings, these scientists concluded that ". .
. knowledge of the cancer mortality experience of an individual will not commonly
have strong predictive value for the experience of another individual who has identical
genes."
Cancer Deaths in Twins
Selected
Cancers
One
Identical
Twin
Both
Identical
Twins
One NonIdentical
Twin
Both NonIdentical
Twins
Stomach
27
0
27
1
Colon or
rectum
90
1
109
2
Liver
10
1
21
0
Skin
18
0
28
0
Prostate
29
0
68
0
Brain or
nervous
23
0
40
0
Cancer Deaths in Twins
One
Identical
Twin
Both
Identical
Twins
One NonIdentical
Twin
Both NonIdentical
Twins
NonHodgkin's
lymphoma
41
0
53
0
Leukemia
17
0
45
1
Selected
Cancers
system
* Smoking-associated cancers not shown
Probabilities vs. RealitiesWhat this conclusion says, basically, is that genes do not
matter, at least for any significant proportion of cancers. To be specific, the probability
of both identical twins getting cancer was only 1.4 times that for both non-identical
twins getting cancer, a result of only borderline statistical significance. Even for one of
the cancers known to have a definite gene linkage from the mechanism point of view (a
certain type of colon cancer), there was essentially no evidence that the mere presence
of this gene actually caused the cancer.To put this 1.4 fold difference into further
perspective, smokers are 8–10 times more likely to get lung cancer than non-smokers,
while people chronically infected with hepatitis B virus are 20–40 times more likely to
get liver cancer than non-infected people. This small 1.4-fold increase, if real, might
even be due to the greater similarity of lifestyles for identical twins than for nonidentical twins. And finally this: these results essentially agree with the findings of four
other smaller studies previously published. In short, this difference, even if real, is so
small that it virtually eliminates genes as an important cause of human cancer.This
brings up some very practical questions. Why is so little attention given to the idea that
it is not the mere presence of "bad" genes but the expression of these genes that matters
most? For genes to cause something, they cannot lie dormant; they must be switched on
or expressed. Thus, why isn't gene expression, especially by nutritional means, given
more attention, both among researchers and between researchers and the general
public? Genetic Deceptions In conclusion, even though I had often thought that genes
might account for a small proportion of human cancers, I am surprised by this finding
showing that genes appear to contribute little or nothing to cancer risk. I would have
thought that we might have seen in this study at least a small genetic effect.The
subjects in this study were men who, in all likelihood, consumed a typical American
diet. With such a diet, whatever cancer-causing genes might have been present should
have been consistently and uniformly expressed as cancer. This was not seen.
Therefore, I must conclude on the basis of these and other data with considerable
confidence that differences in cancer rates between people or individuals cannot be
attributed simply to genes.Obviously, the "gene story" is about much more than genes.
It's about what we eat and what we don't eat. It is also about the great reluctance on the
part of so many of us to change our eating habits. Despite the fact that Americans are
more nutrition conscious than ever before, significant change is painfully slow to come.
During the past 30 years, and especially so in the last decade, the number of overweight
children has more than doubled.T. Colin Campbell is the Director of the CornellOxford-China Diet and Health Project. He was trained at Cornell (M.S., Ph.D.) and
MIT (Research Associate) in nutrition, biochemistry, and toxicology. He presently
holds the endowed chair of Jacob Gould Schurman Professor of Nutritional
Biochemistry at Cornell University.
REFERENCES
Braun, M. M., Caporaso, N. E., Page, W. F., Hoover, R. N. 1995. A Cohort Study of
Twins and Cancer. Cancer Epidemiology, Biomarkers & Prevention 4:469-473.