Shortly after my 54th birthday, I received a package. The enclosed instructions told me that next time I emptied my bowels, I should scrape a bit of the stool into a small sample bottle, seal it in a pre-paid envelope and drop it into the post. I did the deed and, a few weeks later, was invited to hospital. My sample contained blood; a colonoscopy was ordered to rule out colorectal cancer.

I don’t, thankfully, have colorectal cancer, and a colonoscopy at 54 is a classic initiation into middle age. But in the coming years, this particular rite of passage might start happening much earlier. While rates of this cancer among people in my age group have been declining thanks to screening programmes like these, the story for the under-50s is far more troubling.

From being virtually unheard of in the 20th century, early-onset colorectal cancer (EOCRC), as it is called in people under 50, now accounts for around 10 per cent of all new cases worldwide. That number is predicted to more than double by 2030, and by then, EOCRC is expected to be the most common form of fatal cancer in Americans aged 20 to 49.

The reason why is uncertain, but an ambitious new project is exploring potential causes – as well as the idea that EOCRC may be a distinct and more aggressive form of the disease. Meanwhile, as routine screening is extended to younger groups – in January, England lowered its screening age to 50 – and new, less-invasive tests…