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COLON CANCER PREVENTION?
AUGUST 26, 1997
TRANSCRIPT
The Human Genome Project reports that it uncovered a new mechanism by which misspelling a gene can confer risk to cancer. This misspelling is reported to be very common among people of Jewish Heritage.
ELIZABETH FARNSWORTH: Now, new findings on colon cancer. Charles Krause has that.
CHARLES KRAUSE: The new research provides new clues to explain why Jews of Eastern European origin are especially prone to inherit colon cancer. First reported in today's issue of "Nature Genetics," the research may also have broader implications for finding the causes of other types of cancer as well. To tell us more, we're joined by Dr. Francis Collins, director of the Human Genome Project at the National Institutes of Health. Dr. Collins, welcome.
DR. FRANCIS COLLINS, Human Genome Project: Thank you.
CHARLES KRAUSE: What is this new discovery and why is it so significant?
DR. FRANCIS COLLINS: Well, these findings reported by Bert Vogelstein and his colleagues at Hopkins are sort of a double whammy. First of all, they uncovered a new mechanism by which a misspelling in a gene can confer a risk to cancer, one that we hadn't suspected before and which will probably turn out to be generally interesting in other types of cancer as well. But secondly, and maybe more importantly for immediate implications for clinical medicine, this particular misspelling turns out to be very common, found in about 6 percent of Jewish individuals.
Those individuals face approximately a two-fold elevation in their risk of colon cancer, which is a preventable disease. So we have sort of moved from a hypothetical to a real situation where a genetic test might be capable of predicting the risk of a treatable disease in a fairly large number of individuals. That's exciting, and this is sort of the beginning of a new era. It will apply to lots of individuals as time goes on. We've learned about it in the Jewish race initially for this disease, but we're all at risk for things. This is a start down that path, and it should be exciting.
CHARLES KRAUSE: A couple of real quick definitions. You say misspelling. It's not a literally--literal misspelling of the gene, is it?
DR. FRANCIS COLLINS: It's not so different. DNA has its own alphabet. A, C, G, and T are the only letters in it. In this particular instance it's pretty subtle. Where you should have had a T, there was an A. And that single letter out of place seems capable of conferring this approximately twofold increased risk of this dreadful disease, colon cancer.
CHARLES KRAUSE: Second definition. Colorectal cancer--exactly what is it, and where does it develop in the colon?
DR. FRANCIS COLLINS: Well, the colon is the large intestine. It has various parts with various names. Most colon cancer occurs in the distal part, the descending colon, the rectum, which is just beyond that, or in the anal canal. About 2/3 of cancers are in that position. This is a very common disorder. It's the second most common type of cancer after lung cancer. Fifty-five thousand people will die of colorectal cancer in the U.S. this year and a hundred and thirty-five thousand people will be diagnosed. Now, this doesn't sort of strike out of the blue, however. These colon cancers begin initially as benign growths that we call polyps, which if you discover them and remove them, that also removes the risk of developing the cancer. And you've got a number of years to find the polyps before they become evasive and spread elsewhere and threaten your life.
CHARLES KRAUSE: Now, it's not just Jews of Eastern European origin who develop this kind of cancer, is it?
DR. FRANCIS COLLINS: Absolutely not. The risk of colon cancer appears to be about the same in all ethnic groups in the U.S. About 6 percent of us will get this disease at some time. It seems that even in the Jewish population this particular genetic alteration that's been discovered only accounts for a minority of cases. But it is a particular situation where you can identify a subset of folks who are at increased risk. And that might be good for you. Again, if you knew that you had a polyp in there and could get it out, you might prevent the risk of dying of colon cancer.
CHARLES KRAUSE: Did the researchers figure out why it is that the link that they found is only apparently between the variant gene and cancer, is only found in Jews of Eastern European origin--why is that?
DR. FRANCIS COLLINS: The Jewish population has descended from a fairly small pool of founder individuals. And presumably, one of those founders had this misspelling. And it has now been propagated through the generations to modern day Jewish individuals; whereas, many other races are much more outbred, there's much more heterogeneity. But make no mistake, mutations, variations of this sort are present in all of us. Estimates are that we carry from five to as many as fifty significant misspellings in our DNA, each one of us. There are no perfect specimens. It turns out from a scientific point of view it's somewhat easier to find these in a circumscribed group like Jews, or people who live in Finland or Iceland, another favorite topic of geneticists. But that doesn't mean that there is an increased incidence of such alterations in those groups.
CHARLES KRAUSE: There are about 6 million Jews in the United States, most of them of Eastern European origin. Based on the research finding, what percentage of them would carry this variant gene?
DR. FRANCIS COLLINS: Roughly 6 percent seem to carry this, and their risk of getting colon cancer doubles from about the normal 6 percent to perhaps 12 percent. I should say these are very tentative early numbers from a relatively small study. Larger studies will need to be carried out and will be shortly to try to pin them down better.
CHARLES KRAUSE: Quickly, based on--the researchers have developed a blood test to detect this variant gene. Who should be tested?
DR. FRANCIS COLLINS: I think those who ought to be most interested are Ashkinasi Jews, that is, Jews from Eastern European background, who have a family history of colon cancer, because the chances are greatest of finding the alteration there. Even then, individuals interested in that test should have the full facts laid in front of them as part of the process of genetic counseling before deciding whether or not they want to undergo the test.
CHARLES KRAUSE: Now, if they are found to have or carry the gene, does that mean they're going to get colon cancer at some point?
DR. FRANCIS COLLINS: No. It increases the risk, but actually, there's a very good chance--about 88 percent chance--that somebody with this variant will not get colon cancer. And one needs not to sort of assume all of this is a done deal--I know I'm going to get it. It's fairly likely you won't.
CHARLES KRAUSE: At the same time if you take the test and you come up negative, in effect, does that mean you won't get colorectal cancer?
DR. FRANCIS COLLINS: That's a very important point because people might be misled by negative tests into thinking, well, there's a disease I don't have to worry about. In fact, the risk is still the same as everybody else. That base line doesn't go away. And you should still follow the same recommendations. But if you have this variant sequence and your risk is increased, you probably want to start the process of checking out your colon using a procedure called colonoscopy at maybe age 35 instead of age 50 and looking a little more often.
CHARLES KRAUSE: Because this kind of cancer, in fact, is curable, if detected?
DR. FRANCIS COLLINS: Absolutely. That's the good news. This is the kind of cancer, which if you can find it while it's still early, you can snip it out of there and it never goes on to turn into this terrible disease.
CHARLES KRAUSE: Right. Dr. Collins, thank you so much for joining us. Thank you.
DR. FRANCIS COLLINS: Thank you.
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