When it comes to cancer research, we regularly hear good news about the number of people benefiting from advances in treatment. But there is one bad news story about the condition that gets little attention. For three decades, there has been a gradual rise in the number of people under 50 being diagnosed with cancer – and we don't entirely know why.
The rise is steepest in bowel cancer, but an increase in incidences is happening with tumors of nearly all the major organs of the body. It is so alarming that it was made a top priority for research in a joint UK-US cancer funding review earlier this month. So, what might the causes be?
The incidence of cancer rises with age, mainly because the cells of older people have had longer to acquire the genetic mutations that cause tumors.
Around 9 in 10 cancerous tumors occur in people over 50, so the increasing incidence in people younger than this isn't making a big impact on the total number of cases. "It's important to remember that the vast majority of cancer cases are diagnosed in people over 50," says Alice Davies at Cancer Research UK (CRUK).
Yet the trend is worrying, partly because it shows no signs of stopping. Young people should be in the prime of their lives and are often caring for children, says Marios Giannakis at the Dana-Farber Cancer Institute in Boston, Massachusetts.
"It's an absolutely devastating day when you see young patients diagnosed with cancer," he says. Giannakis called for an investigation into the reasons behind the rise in bowel cancer specifically in an opinion article in the journal Science on March 16.
For most types of tumor, their increase in people under 50 has been relatively modest so far. For instance, the incidence of all cancers combined among 25 to 49-year-olds in the UK rose by 22 percent between 1993 and 2018, from 133 cases per 100,000 people to 162 per 100,000.
But the fact that the same trend is being seen in many different cancer types in high, middle and low-income countries suggests that it should be seen as an emerging global epidemic, said Shuji Ogino at Harvard Medical School in a review of World Health Organization figures last year. "I believe the trend won't stop anytime soon and it may accelerate," he says.
The figures for bowel cancer are the most alarming, with about a 50 percent rise in people aged 25 to 49 since the 1990s in the UK, for example. There is a similar pattern in the US, Canada, Australia, South Korea and several European countries, including Sweden, Finland and the Netherlands.
At first glance, the phenomenon might be ascribed to the relatively recent practice of cancer screenings finding tumors that wouldn't otherwise have been noticed, but this could only be causing some of the increase. In the majority of countries, screening is only offered to people from about the age of 50, depending on the tumor type. Most of the cancers that are rising also can't be screened for.
In addition, the rise in bowel cancer seems steepest among those in the youngest age bands, who are rarely offered screening. Across 20 European countries, the rise has been by about 2 per cent per year in people in their 40s, 5 per cent in those in their 30s and 8 per cent in those in their 20s.
This suggests that whatever the cause is, it is intensifying, says Manon Spaander at Erasmus University Medical Center in Rotterdam, the Netherlands, who helped to demonstrate this decade-based pattern in a 2019 analysis.