TOPICS > Science

Genetic Map of Certain Cancers Discovered; Cancer Rate Drops

September 7, 2006 at 6:40 PM EDT

JEFFREY BROWN: The news is promising on two fronts. The
journal Science reports that researchers have made important discoveries about
the genetic underpinnings of cancer.

Meanwhile, an annual report indicates, the death rates from
cancer in the United States
continue to fall. And new diagnoses of some cancers, notably breast cancer, may
have leveled off.

Here to tell us more is health correspondent Susan Dentzer. Our
Health Unit is a partnership with the Robert Wood Johnson Foundation.

Susan, let’s start with the genetic research here. Now, the
background to this is new awareness that cancer is, at its core, a genetic
disease, right?

SUSAN DENTZER: That’s right, Jeff, that it starts with
changes in genes, mutations or other changes that take place. And that’s the
premise behind something called the Cancer Genome Atlas, which is a large
federally funded project getting under way, under the auspices of the National
Institutes of Health, to essentially draw up a catalogue of all of the genetic
changes that can take place that can lead to cancer.

We know we have about 30,000 genes in the human body. Some
unknown, but meaningful percentage of those can mutate or undergo other
changes, which, in turn, lead to changes in cells, which, in turn, leads to

So, if we can come up with this giant catalogue, we can
really develop a very thorough understanding of what really causes cancer, at
its genetic roots, and then come up with very targeted therapies to attack
those things that are actually matched to the genetic roots of an individual

Tailoring cancer treatments

JEFFREY BROWN: All right. So, tell us about this particularresearch. What did scientists do?

SUSAN DENTZER: These scientists actually showed that thatstrategy underlying the Cancer Genome Atlas could work.

They took 11 different breast cancer tumors and 11 differentcolon cancer tumors. These are tumors that, collectively, represent about oneof every five cancer diagnoses a year in the country. So, it's a significantspread of cancer.

JEFFREY BROWN: That's why they chose those two cancers?

SUSAN DENTZER: That's why they chose those, yes, and thoseparticular subtypes of cancers in those tumors.

They looked at those. They performed a very, very high-techscreening process, in effect, and essentially found, at the end of thatprocess, that there were almost 200, 189, genetic mutations, most of which werepreviously unknown, that actually were contributing, if not in fact causingthose cancers.

So, it's almost a way of saying they came up with a littletiny paragraph in this long catalogue that will ultimately be developed. Butthey showed that, in fact, through this process, you really can come up withmeaningful discoveries.

And, in fact, one researcher described these as a treasuretrove, in and of themselves, with respect to these two different types ofcancer.

JEFFREY BROWN: So, the way for the rest of us to think aboutthis, maybe, is that it's a strategy for how to develop what?

SUSAN DENTZER: It's -- in the end, it will be a strategy fordeveloping very sophisticated, so-called targeted therapies, that actually lookat the actual genetic changes that lead to a cancer.

What we have now to fight cancer, once we have diagnosed it,are very blunt instruments. We have chemotherapy. We have radiation. They comein, irrespective of what is causing your cancer genetically, and they wipe outlots of cells, including the cancer cells.

So, they're very blunt instruments. What the future holds,and what we see now in certain drugs, like the breast cancer drug Herceptin, isa drug that is specifically matched to the set of genetic changes that happenthat trigger a particular subtype of cancer.

We know that there are many, many different types of breastcancer. If we could figure out specific, targeted therapies, something thatgets in, that either switches a gene on or off, blocks a protein that a mutatedgene might contribute to the body, whatever, we will be able to come up withthings which will be much more effective, probably much less toxic toindividuals than chemotherapy or other things are.

Now, it's important to say, these things are not going to beflying off the shelf tomorrow.

JEFFREY BROWN: Right. That was the next question.

SUSAN DENTZER: This is a long, long process.

JEFFREY BROWN: I mean, this is -- as you said, this is justpart of mapping this atlas. So, that's...


JEFFREY BROWN: ... where the research continues?

SUSAN DENTZER: That's right.

And then, of course, we have a long path ahead of us, interms of developing these therapies, testing them for their safety, etcetera. Butwhat it tells you is that, over the next 20 and 30 years, the strategy forfighting cancers is going to change remarkably, both in terms of preventingthem and getting them very early on in the process, and, in effect, treatingthem very effectively.

Successes against cancer


So, the second bit of news involves data from what'shappening in the last few years. Let's just look at a snapshot of right now. Generallyspeaking, cancer rates are on the decline, continuing to decline, correct?

SUSAN DENTZER: Cancer death rates.


SUSAN DENTZER: And, of course, that's the gold standard.


SUSAN DENTZER: That really shows that progress has been madeagainst fighting cancer, if you have fewer people dying. And, in effect, therates...

JEFFREY BROWN: Death rates, as opposed to incidence?

SUSAN DENTZER: Incidence, that is to say, new diagnoses ofnew cancers.


SUSAN DENTZER: And, in fact, cancer death rates overall havebeen declining since the 1990s. And the trend is being perpetuated into thepresent, across the board in the major cancers that affect both men and women,and across all races. So, that's very good news.

One of the big drivers of that, for example, is lung cancerdeclining in men, because fewer and fewer men are smoking. So, those areimportant trends.

The other trend, though, is the one you alluded to, which isincidence, that is to say, new diagnoses of cancers. And, across the board,we're seeing many of those rates stabilize, or, in some cases, drop.

Now, it's not everything.


SUSAN DENTZER: For women, for example, incidence of melanomais going up; incidence of lung cancer is going up. So, again, it's notuniversal.

But the big one that people were getting quite excited aboutwas that new diagnoses of breast cancers seem...


SUSAN DENTZER: ... to be leveling off. And that's important,because those rates were climbing in the 1980s, and giving people a lot ofconcern.

If we get more evidence in future years that those rates arecontinuing to stabilize, or even decline, that will be very good news, indeed.

Meaning behind the data

JEFFREY BROWN: So, that is great news, for the moment, onbreast cancer. But you're saying that it's -- still, the jury is out on whetherhow meaningful that is.

SUSAN DENTZER: Right. You really want to see several yearsof data cropping up, showing the same thing.

And, also, frankly, there are other things in theenvironment, we know, which could drive things the other way.

We know that rates of obesity among adult women are rising. Obesityis correlated and linked to breast cancer rates. So, we can't pop the champagnebottle yet. We will have to see how these trends play out over time. But, atleast for now, there's some sense that the rates -- that new diagnoses arestabilizing.


And is there any thinking on why that is happening?

SUSAN DENTZER: Very speculative at this point, but one ofthe points of speculation, for example, is that hormone therapy use among womendropped off sharply once, in 2002, it was reported, the major federal studyreported, that there were higher breast cancer risks attendant using hormonetherapy.

A lot of women went off it at that point. It could be thatwe're beginning to see some signs, in terms of the cancer diagnoses, that thattrend in fact played out.

But, again, it's speculative. And, really, it will takeseveral more years of data to find out what really happened.

JEFFREY BROWN: All right, Susan Dentzer, thanks again.

SUSAN DENTZER: Thanks, Jeff.