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Genetic test to classify tumours

Friday 19 February 2010

A new genetic test could be used to detect cancer cells lingering after treatment, according to several newspapers. They also say the technology could be used to tailor treatments to each patient’s genetic cancer profile.

This story is based on a press release highlighting the development of a blood test that is able to detect DNA released by tumours in the bloodstream. The test screens a patient’s whole genome and looks for changes in large sections of DNA rather than looking for single mutations in a specific gene.

It is hoped that this test will provide an alternative method to detect whether tumours are still present after treatment, a task currently performed using CT scans. The experimental test may also allow researchers to screen for the variety of genetic changes that are present in tumour cells, mapping how these cells will respond to different treatments.

Where did this story come from?

News reports on this technology are based on a press release from Dr Victor Velculescu and colleagues at John Hopkins University. Their press release discusses forthcoming research, which will be presented at a US conference and published in a medical journal next week.

In the research the scientists made use of new genome sequencing techniques to look for large changes in the DNA released by tumour cells. The aim of the research was to say whether these tests could be used to detect specific biological markers for cancer in each patient’s blood.

How was the research performed?

The study compared six sets of cancerous and normal tissue from patients with colon or breast cancer. The researchers scanned all of the DNA in each sample and looked for DNA rearrangement, repetition or deletions of DNA sequences They also checked whether DNA sequences had the correct ordering, orientation or spacing.

The researchers then amplified the levels of normal and tumour DNA in the blood in order to determine whether these tests were sensitive enough to detect the presence of rearranged tumour DNA in these samples. They found that in one patient they could use this technique to detect that not all of their tumour had been removed during surgery.

What is the theory behind a blood test to measure cancer?

This news story is based on research that has studied the genetic profile of patients with cancer in order to develop individualised blood tests that may help doctors to tailor patients' cancer treatments.

One of the properties of tumours is that they can differ from normal tissue in the amount of different types of protein that they produce. They can also vary in their genes and the proteins that are produced on the surface of different tumours, even between patients with the same type of cancer. These genes and proteins may determine how effective a particular cancer treatment will be in destroying the cancer cells and preventing them from spreading.

The genetic changes in tumours can be small alterations in the sequence of genes, but are also thought to include changes in large sections of DNA. In these large changes whole sections of DNA may be repeated, deleted or appear in the wrong order.

Currently CT scans are used to visually detect the presence or absence of tumours after treatment. However, very small tumours may not be detectable by this method. As tumours release small quantities of their DNA into the bloodstream, it may be possible to devise a blood test that will  chemically measure the presence of abnormal DNA. Theoretically, measuring this tumour DNA in the blood may also make it possible to monitor whether a treatment has been effective in fully destroying a tumour.

Will this research lead to personalised cancer care?

It is already established that changes found in specific genes of tumours can govern how the tumour responds to different types of cancer treatment. This is preliminary research shows the potential to use this property to aid detection of the cancerous cells that may persist after treatment. However, the researchers would need to assess the technology in a larger number of patients with different types of tumours in order to know how well the blood test can predict the presence or absence of a tumour. This would be especially true in smaller tumours that may be harder to detect or remove.

Another potential problem would be the cost of any tests developed from this research. The technology currently used to examine the patients' genes is more expensive than CT scans, and is estimated to be in the region of $5,000 per patient.  

Also, as preliminary research, this technology does not appear to have assessed how strongly large DNA changes affect a tumour’s response to treatment. Therefore, it is too early to say that doctors are close to being able to provide made-to-measure cancer treatments based on the genetic make-up of an individual’s tumour. However, this development may be an important early step in that direction.

Analysis by Bazian
Edited by NHS Website