A blood test to find over 50 cancers could be the future of early diagnosis

Source: Tim Peacock, the MIT Technology Review.

This blog was written by Mairéad Lyons. Mairéad is a Senior Consultant to YouScreen the HPV Self-Sampling study.  She has been working in healthcare for over 30 years, first as a nurse, then in health promotion before moving into public policy research and service improvement.  The last ten years she has worked to improve patient outcomes through earlier diagnosis and standardisation of cancer service provision in Ireland and England.

Last week’s headlines (BBC, independent) about a new test that could detect up to 50 cancers in blood made for a welcome reprieve from coronavirus debates.  It is an exciting breakthrough and one that we, in the health and science community, are following closely.  It left me wondering what could it mean for the early detection of cancer or the future of cancer screening in the population.

Like the many thousands, indeed millions of people who are stuck at home during the Coronavirus lockdown, I started tackling the spring clean, a job no longer avoidable.  In a file heading for the bin, I found a list of family members and one friend, who had been diagnosed with or died from cancer.  There were seven blood relatives (5 now deceased), a sister-in-law and my best friend both of whom died in their 40s.  How would this test have changed their lives, how could it change mine in the future?

If this test can find cancer at an early stage then it will undoubtedly save lives.  Finding cancer early not only saves lives, it can also improve quality of life for patients, extending survival in many cases and reduce the need for intensive and complex treatments.  Earlier diagnosis has become the cornerstone of NHS efforts to improve cancer outcomes. The NHS Long Term Plan has set a goal that by 2028, 75% of people with cancer will be diagnosed at an early stage (stage one or two).

Of the family and friend above who have died from cancer, their diagnosis occurred when they were symptomatic, acutely unwell and admitted to hospital.  Then began the diagnostic process of multiple investigations, emergency surgery in two instances, radiotherapy and intensive chemotherapy in all cases.  The cancers – Lymphoma of the intestine, Bowel Cancer, Leukaemia (AML), Prostate Cancer, Oesophageal Cancer and Uterine Cancer – were advanced in all but one case.

Using Artificial Intelligence, the new blood test can detect up to 50 cancers in the blood.  The overall specificity of the Grail test was 99.3%.  This is important as specificity is the ability of the test to correctly identify those without cancer.  We know that in 0.7% of cases it wrongly detected (a false positive) cancer.  The sensitivity of the test (the ability to correctly detect cancer when it is present) was better in late-stage disease than earlier stages; only 18% of the stage 1 cancers were found versus 93% of stage IV.

In some specified cancers (anus, bladder, colon/rectum, oesophagus, head and neck, liver/bile duct, lung, lymphoma, ovary, pancreas, plasma cell neoplasm and stomach) this detection rate was better with 39% of stage I and 92% of stage IV identified. In 93% of positive samples from patients with cancer, the Tissue of Origin was correctly identified.  (Figure 5 in the paper).  Results showed an overall sensitivity of 55% for all cancers (stage I-IV) and 78% (stage I-IV) for a pre-specified list of 12 cancer with a specificity of 99.3%.

This study looked at blood samples from 6,689 participants (2,482 with cancer and 4,207 without).  The computer programme was trained, using an algorithm or code that told it to look for methylation changes and classify the samples as cancer or non-cancer in one set of samples, the training set.  Then the results were checked in another group of blood samples, the validation set.  The researchers found that the test when searching for these classifiers had a false positive rate of less than 1% across more than 50 cancers in both training and validation groups.

The promise is there. The Grail test may be even more useful for cancers that are difficult to find early such as pancreatic cancer.  The study showed the detection rate for pancreatic cancer was 63% for stage 1, 83% for stage II, 75% for stage III and 100% for stage IV.  The Grail test has potential to transform outcomes for pancreatic cancer patients.  Less than 5% of patients with pancreatic cancer survive 5 years or more, this could change significantly in the future.

A simple blood test could be a very useful cancer screening tool if effective at finding cancer before symptoms develop.  Many of the challenges we face with trying to detect cancer before it becomes symptomatic (screening) is getting the population to take up the offer.  For many critics of population screening doing more harm than good is a key concern.  Population screening aims to strike a balance between overdiagnosing or overtreating benign or non-cancer conditions and detecting sufficient numbers of cancers that make a meaningful difference to mortality rates and survival.  Simply put, it must save lives and cause little harm.

People might go to their GP or to a screening centre that offered one blood test that could find bowel, breast and cervical cancer instead of having to participate in multiple screening programmes.  An Australian study reported that 78% of study participants would prefer a blood test for screening of cancer.  Our knowledge of the gains to be achieved by these screening programmes could make one blood test a highly valuable tool for implementation.  Depending on how it would be deployed, it could address many of the barriers to participation. It could lead to significant cost reductions, making resources available for use elsewhere in the system.  The Grail test holds such promise and potential.

If its accuracy is developed further to detect cancers at stage I or stage II, then it could enhance the work of GPs to rule in cancer when assessing the patient presenting with vague symptoms.  GPs could more easily identify the specific investigations for which they should refer the patient, reducing the flow of patients into hospitals for unnecessary tests and ease pressure on our otherwise bursting NHS.  It is a test that could also be used in association with a risk assessment tool that could screen or select patients who, due to family or lifestyle histories, may be at increased risk of developing cancer.

It is exciting, hopeful and fills me with optimism that this discovery will transform our experience of cancer in the future.

The views expressed are those of the author. Posting of the blog does not signify that the Cancer Prevention Group endorse those views or opinions.

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