Study unravels breast cancer code

By Steve Connor

Photo / Thinkstock
Photo / Thinkstock

Cancer is the quintessential genetic disease, so it comes as little surprise to find it has benefited most from the unravelling of the human genome - the blueprint of life written in the digital DNA code of the cell's chromosomes.

It is now more than 10 years since the full DNA sequence of the human genome was first published and the benefits of that understanding are now apparent in a remarkable breakthrough in breast cancer genetics.

For the first time, scientists have been able to tease apart differences in the DNA of breast cancer patients that go far beyond the results of classical medical science, based on the tradition of analysing tumour tissue under a microscope.

Researchers have used advances in genetics to determine 10 subtypes of breast cancer, each of which has a unique genetic fingerprint that could in the future determine a patient's tailor-made treatment - or cure.

At present, breast cancers are classified according to the presence or absence of a few "markers" or proteins found on the surface of tumour cells.

In future, doctors will classify breast cancers based on the presence, absence or even activity of the smallest bits of DNA code.

The power of the latest study, published in the journal Nature, resides in the ability to retrospectively analyse some 2000 frozen samples of breast-tumour tissue collected from women in Britain and Canada between five and 10 years ago.

Using powerful new developments in DNA analysis, such as computer-controlled "micro arrays" that can automatically scan the entire three-billion-letter code of the human genome for the smallest of mutations, scientists were able to confidently pigeonhole each tissue sample into one of 10 subtypes.

Each subtype had defined characteristics in terms of DNA variations and gene activity. The scientists could also show that each subtype displayed subtle but important features in terms of a patient's prognosis - in other words the DNA differences mattered.

Instead of looking at breast cancer as a single disease with a limited range of treatments, the scientists believe that their breakthrough demonstrates a range of cancer subtypes that can and should be treated differently.

"Our results will pave the way for doctors to diagnose the type of breast cancer a woman has, the types of drugs that will work, and those that won't, in a much more precise way than is currently possible," said Professor Carlos Caldas of Cambridge University, a senior member of the Anglo-Canadian research consortium.

"Essentially we've moved from knowing what a breast tumour looks like under a microscope to pinpointing its molecular anatomy - and eventually we'll know which drugs it will respond to."

It would mean that breast cancer patients in the future would have a genetic test before doctors decide on which treatment options to consider. This would end the blunderbuss approach of past therapy, leading to custom-designed "silver bullets" to treat cancer subtypes.

"This has the potential to change the face of breast cancer; from how we diagnose and treat it, to how we follow it up," said Julia Wilson, head of research at the charity Breakthrough Breast Cancer.

At present, some patients are receiving treatment that serves no benefit and is likely to have harmful side effects.

The DNA revolution could change this, although scientists emphasised it will take many years before patients experience the benefits first-hand.

"I want to be very cautious here. This is a very important first step, and now what follows is to validate its clinical use," Caldas said.

One of the first groups to benefit, he said, would be patients who are currently being "over treated" with potentially toxic drugs because current tests do not distinguish between those patients who will benefit from a particular drug and those who do not.

The study, carried out in co-operation with the University of British Columbia in Vancouver, also discovered that certain genes are involved in either driving breast cancer or holding it back from spreading.

Some of these genes are known to be involved in the production of enzymes within human cells, which will make them attractive targets for the development of new anti-cancer drugs, said Sam Aparicio of UBC, the study's co-leader.

- Independent

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