More than half a million Americans die of cancer each year, matching the toll of Covid-19 to date on an annual basis and making it one of the nation’s biggest killers. But now there’s hope that a simple blood test could change that by detecting tumours earlier, when they’re easier to treat. 

Grail, a biotechnology start-up, launched a blood test called Galleri in the US in June and published data validating its ability to detect otherwise hard-to-find tumours. While blood tests already exist for individual cancers, Grail’s caught 29 different types of the disease in a real-world experiment. If these tests prove effective, they could slash cancer’s burden, so unsurprisingly the news received a lot of attention. But is it more hype than hope? There’s promise, for sure. It’s essential, though, to acknowledge some realities of cancer screening that may hold these tests back. ..