GALLERI: The Holy Grail for cancer diagnosis?

We all know that there are multiple challenges to the early diagnosis of cancer for us in primary care, one of the big ones being a lack of access to accurate tests for cancer. There are obviously exceptions (the FIT test has undoubtedly helped bowel cancer diagnosis), but the majority of tests we have access to generally have low sensitivity and specificity, and our secondary care colleagues are left making a difficult judgement on when to use more invasive tests that are either unpleasant, expensive or both. But what if we had access to a simple blood test that could give a signal to 50 different cancers on the one test? 

Well, (cue gruff TV personality intro): Welcome to the Galleri test, designed by GRAIL. This test caused quite a stir last year when the NHS-Galleri screening trial was announced, but what is it and why all the fuss? Now I’m no genetics expert, so apologies to any of you with greater knowledge and skills than me! But my take on it is this: DNA methylation (the process of methyl groups attaching to DNA) is one process that causes activation or repression of genes (i.e. it helps govern whether the gene is switched on or off). Cancer cells have abnormal patterns of methylation which then promote/switch on tumour growth. All cells shed DNA into the blood stream (cell free DNA/cfDNA) including cancer cells. The Galleri test is a novel test (via a single blood test) that identifies patterns of methylation of cfDNA, and it is these abnormal methylation patterns of the cancer cfDNA that the test can identify. Pretty neat! 

Sounds pretty good already but there are two big differences with this test compared to the current blood tests we have available in primary care for cancer screening or diagnosis. The first is that it is known as a Multi Cancer Early Detection (MCED) test, so it is not just looking at one cancer type but can pick up abnormal cfDNA methylation patterns for multiple cancers (about 50 currently) and can then give an indication as to which cancer is present. Second, if the preliminary data is to be believed, (and this is a big ‘if', and one that we will only know after more data comes out) the test has a very low false-positive rate with current claims that the false positive rate is <1%, making it a highly specific test for cancer. Compare that to the current blood tests we have for cancer detection in primary care - PSA has a false positive rate of ~75% and Ca125 somewhere in the region of 50-70% (albeit this will vary considerably depending on the population looked at and whether they are symptomatic or not) and you can see why everyone is getting so excited about the Galleri test. 

So this test could (potentially) be used for both population screening (which neither PSA nor Ca125 are effective for) and for people presenting with non specific symptoms which may be due to cancer, and indeed early data suggests this test may be able to pick up some of those difficult to diagnose cancers at earlier stages. We have two trials in the UK which are investigating Galleri. First the SYMPLIFY study, which will recruit 6000 symptomatic people and analyse and validate Galleri compared to standard cancer tests. The second is a screening RCT, the NHS-Galleri trial, which will recruit 140,000 asymptomatic people aged 50-77 to assess if Galleri is a useful and accurate screening test. Cancer Research UK have more information here. 

So potentially exciting times in the world of cancer diagnosis! It will obviously be a while till we know how effective and accurate Galleri is, but in the mean time if you need a review of everything cancer related - everything from updates on screening programmes and the latest evidence and guidance for early cancer diagnosis, to cancer related complications and end of life care, why not join Kate and Sarah and myself this Saturday 5th February for our comprehensive LIVE Cancer Course Webinar.