In the news this week we’ve heard about a new trial that will look at developing a blood test to detect cancer. Consultant Breast Surgeon and Head of our Medical Advisory Board, James Harvey, shares his thoughts:
‘It is fantastically exciting that the NHS is trialling blood tests as potential screening procedures for detecting cancers. The NHS is committed to using the tests on approximately 140,000 patients on a trial basis. The technology is essentially looking for cell-free DNA in the bloodstream; this means that it is looking for the genetic material that has been released from cancer cells that can be present in the blood.
The test is screening for 50 different cancer types. There has been a lot of excitement in the scientific community on the potential to detect cancer DNA on a blood test for some time. The process of testing for DNA has become more accurate and cheaper meaning that it is now potentially feasible as an affordable method of screening.
Does this mean we will be able to detect cancer on a blood test?
Yes, the test can definitely detect cancers. In early studies, the test was able to detect up to 2/3rds of cancers of the oesophagus, liver and pancreas, compared to 1/3rd of breast, bowel and prostate cancer. The test is also accurate because the false positive rate is very low (i.e. the number of people who have a positive test result but don’t actually have cancer).
So the test will be able to screen for cancers?
This is a more subtle question. Certainly, the test is able to detect cancers. One of the most important considerations is that the higher the stage of the cancer, the more likely the test is to detect a cancer i.e. the larger the cancer and the further it has spread, the more likely it is to have been diagnosed.
For instance, in early studies the test detects 1 in 6 stage I cancers, but 90% of stage IV (metastatic) cancers. Clearly, the higher the stage of the cancer at the time of diagnosis, the less likely the patient is to be cured long term. This makes sense – if the patient has cancer cells or cell-free cancer DNA in the bloodstream it is more likely that some cancer cells will be spreading in the bloodstream to other parts of the body. The idea of a screening programme is to detect cancers at an early and curable stage. Detecting them at a later stage still has potential benefit for patients in having an earlier diagnosis but may make little difference to cure rates.
Currently breast cancer screening with mammograms is relatively good at detecting precancerous cells and Stage I disease compared to a blood test as the vast majority of these patients do not have cancer DNA in their bloodstream.
Having said this the use of the test in the NHS will give this technology a huge boost, it will enable thousands of patients to be assessed and for the tests to be improved using the data collected as part of this study. It will enable the company involved and the NHS to get much more information about which cancers this may be useful for and in which patients.
I am certainly excited by this large study and what it will mean for cancer patients in the future. I think one group of patients that will potentially get huge benefit and reassurance from this technology is primary and secondary breast cancer patients. This technology can potentially be used to track patients who are in remission and a regular blood test every few months may be a way of detecting early recurrent disease. This may mean an earlier diagnosis and earlier access to treatment.