News reports on this technology are based n a press release from Dr Victor Velculscu and colleagues at John Hopkins University. Their press release discusses forthcoming research that 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 this blood test?
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 patient’s 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 changes in the sequence of genes but are also though to include changes in large sections of DNA. In these large changes whole sections of DNA may be repeated, deleted or in the incorrect 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 destroying 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 potential to use this property 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 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 patient’s genes is currently more expensive than CT scans, 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.