Gene May Tell Who Is Likely to Get Breast Cancer

Health contributor Dr. Bernadine Healy talks about a new gene study that could eventually lead to a simple blood test--a test allowing women (and men) to learn whether they have a genetic profile that puts them at risk for breast cancer.

In today's New England Journal of Medicine, the lead article is "Gene-Expression Profiles in Hereditary Breast Cancer." In simple terms, researchers examined the genes in breast cancer tumors from 21 subjects (including one man) to find gene "profiles" for the cancers. Essentially, the researchers found three types of breast cancer, based on three different gene-protein patterns.

Currently all breast cancer is treated with the same therapies. Now that we know there are at least three different types of breast cancer, researchers can focus on therapies that are specific to the particular gene-protein pattern behind that particular breast cancer.

Interview with Dr. Bernadine Healy

This is an intriguing study in the context of the human genome. We learned that we only have 30,000 genes, not the 100,000 we expected. We have only twice as many genes as a worm, and only a small multiple of the number of genes a flea has.

A key element in understanding genes is the proteins they encode. We've been hunting for the breast cancer gene for years. In 1994, we hoped we could instantly apply this to clinical care--hoped it would instantly enable us to come up with treatments and gene therapies. What we've learned since is that just knowing a gene is many steps from understanding how that mutated gene produces the proteins that lead to a cell becoming cancerous.

Last week everyone said we were moving from genomics to proteomics. Protein is what genes encode: Proteins are the actors, the hormones, the growth factors. They form receptors. They are the molecular operators of our cells and tissues

What does the study tell us?

What this article says is that you can't just look at a mutation: You have to understand the gene expression profile. What do these genes direct in terms of proteins in that cell? In some cases, the gene-gene team produces something that could be aggressive cancer, or can be modified or corrected by the other, so the outcome is that you will not get cancer. Remember that none of these is 100% sure. Even the highest estimate is 80%.

The bottom line--this tells us that just because you have the gene doesn't mean you'll have cancer, but the downstream process of creating proteins within the cell will determine if the cell will be healthy or not healthy. That gives the opportunity to predict but also to come up with specifically tailored angles. When you understand that it's not just the genes, but the protein they produce that determine the cancer, you can understand why two women can have the same gene but one has cancer and the other not.

You can't do anything about your genes. But it's useful to know if you have a genetic endency, because it makes you more vigilant. Most of the reduction in mortality relates to what women are doing: breast exams and mammograms. And if a woman does get breast cancer, a woman's chance of surviving goes up.

We talk about two genes for breast cancer discovered in 1994. But this shows us that these mutations influence distinct patterns. Everybody with breast cancer genes doesn't have the same outcome. It's not just one gene, one protein and you get the disease. Rather you have the gene, and there is a whole array of patterns that will differ from one another.

Does it matter what your profile looks like if you know you've got breast cancer?

Yes, because not all breast cancer is the same. There are many different types, and they affect how aggressive the cancer is, how rapidly it spreads, its likelihood of coming back, whether or not it is hormone sensitive. And all of those will influence therapeutic decisions. So the notion that all breast caners are the same is wrong.

This research involved 21 subjects: seven women with a breast cancer 1 gene mutation, seven with a breast cancer 2 mutation, and seven with "sporadic" breast cancer. Is that a wide enough sampling?

These were very complex genetic studies, so they actually got a lot of data from each of these tumors. And it was a wide enough sampling to answer the questions they were trying to answer: Not all the patterns were the same. This opens many lines of investigation for drug therapy.

Will this research ultimately lead to a genetic "screening" test that will warn women they may get breast cancer?

In all likelihood it will. There will be molecular patterns directed by these mutations that may signal that you carry this gene. A simple blood test may be developed to show whether you have that mutation or are at risk.

Isn't all breast cancer hereditary?

No, only 10%--about 90% are sporadic. The hereditary forms teach us a lot about breast cancer. The hereditary types tend to occur in younger women. They are more likely associated with gene abnormalities. As women get older, it tends to be sporadic, but also more frequent. About 20% occur under the age of 50 and 80% occur over the age of 50.

Usually breast cancer is more aggressive in younger women, but not always. Familial breast cancer genes are also associated with ovarian cancer, and in some cases in men with prostate cancer.

Knowing you have the breast cancer gene can lead to implications for the entire family, possibly also colon cancer. The genes can be a "marker" for being more susceptible to certain cancers.

What is the prevalence of "sporadic" cancer?

In the study, someone with sporadic cancer had a pattern of proteins that looked like the mutation. An interesting subset that suggests if you come up with a treatment for that pattern, it may be applicable to the sporadic cases as well

STRONG>Is one gene mutation "worse" than the other is as far as "severity" of breast cancer is concerned?

It's not that one is worse. One is more likely to be associated with colon cancer, or ovarian cancer. There are distinctive patterns, but also overlaps.

Does this new research provide a magic bullet?

What it provides is an understanding that points the way to more targeted anticancer treatment. We now tend to use the same drugs for all breast cancer. But this study opens the exciting possibility of having different drugs for different molecular patterns.

Essentially the researches have created three subsets of breast cancer. So from there you could have three or four different drugs that behave differently on these patterns. For example, Herceptin is a receptor drug that came on the market last year. It's a very targeted molecular drug that focuses on a receptor related to one gene. So it's not so far away.

One of the patients was a man. Does this mean men carry the gene and can get breast cancer?

Men can get breast cancer. But the numbers are way under 10%. These genes are associated with male breast cancer. It's very rare because they don't have estrogen.

What other genetic traits did these patients have in common?

Mainly the X chromosome and female patterns of estrogen metabolism. There are many other genes interacting or modifying that may affect receptor molecules. The biochemical patterns are just starting to be filled in.

Proteins more important than genes

Scientists mapping the human genome were surprised to find a human has only twice as many genes as a worm, but their findings open up a whole new frontier for public and corporate researchers alike--the study of proteins.

Apparently, people have only 30,000-40,000 genes instead of the 60,000-100,000 originally predicted. Significantly, it seems that each gene may be responsible fr several different proteins. And interactions of genes and proteins they control are far more important than the actions of a single gene.

What does that mean for the doctors and scientists and researchers who were hoping the gene map would aid them in curing illnesses, creating custom-made drugs and predicting who is most at risk of certain conditions such as heart disease? More work! Instead of having to understand 30,000-40,000 genes, researchers have to learn about 250,000 different proteins and their various profiles.

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