More than 350,000 people are diagnosed with cancer each year in the UK.

But this number is changing.

New figures we’ve released today estimate that by the year 2035, half a million people could be diagnosed with cancer each year in the UK. To think about it another way, that’s equivalent to the population of Liverpool hearing the words ‘you have cancer’ every year.

So what’s behind this staggering figure? It’s a complex picture. And – crucially – there are ways we could stop the number of cases of cancer ever reaching this much. We’ll discuss more on this later.

But, first, to understand what the numbers really mean, you have to get your head around the difference between cancer cases and cancer rates.

Rates and cases – what’s the difference?

Cancer cases are the number of people in a population who are diagnosed with cancer in a particular year – as mentioned, there were over 350,000 cases of cancer in the UK in 2014.

You would think this is basically all we need to know about cancer numbers. But changes in cases over time can be misleading. That’s because the population of a country also changes massively over time – both in number, and in the proportion of people in different age groups.

Here in the UK, the population has grown a lot in recent years because people are living longer.

So there are more people around, and also the proportion of older people in the population is growing. And as we get older, our risk of cancer increases. This, as our graphic below shows, accounts for most of the forecasted increase in cancer cases.

This is important information for people involved in running the NHS, as more investment will be needed to diagnose, treat and care for all these extra cases of cancer. But it doesn’t quite get to the bottom of how we can limit our own chances of getting cancer.

It’s not just changes in the population that affect the number of cases. Our risk of getting cancer is also is influenced by being exposed to things that cause cancer, for example smoking.

And that’s where cancer rates come in.

Rate calculations are based on a representative standard population that doesn’t change over time.

Using this artificial population means that without the confusion caused by changes in the actual population, researchers can begin to understand how changes in different causes of cancer – for example smoking rates or obesity – might affect how many people are diagnosed with cancer over time.

Cancer rates are increasing in women

Research based on data up to 2007 suggested that cancer rates for both sexes would stay the same over the 20 years that followed. And that holds true for men according to the new figures we’ve published today.

But a different picture has emerged for women; cancer rates are now projected to increase in the coming years.

This doesn’t mean that the previous research was wrong. Instead, in the years since it was carried out, women’s risk of getting cancer has increased.

But why is this? Let’s look at an example.

Women and smoking

If you want to understand lung cancer rates today, you have to look at smoking trends many years in the past. It takes time for damage to cells to accumulate, so it often takes many years of exposure before cancer develops.

In 1950, it became clear that smoking can cause lung cancer.

Following this, smoking rates in men have declined fairly consistently.

And since the 1970’s, lung cancer rates have also followed this trend in men. But the pattern looks different in women.

There were always a smaller proportion of women who smoked. But following the news that smoking causes cancer, smoking rates didn’t fall in women. In fact, they slowly but steadily increased, and didn’t begin to fall until the late 1960’s.

As a result, and as our graphic below shows, lung cancer rates in women have still not yet peaked. And today’s figures suggest that they won’t start to decline for several years.

So, is smoking the only problem?

Unfortunately not. Though smoking remains a massive problem, it’s not the only problem.

The number of UK adults who are overweight and obese has now crept up to just under two thirds of the population.

Being overweight or obese can cause 13 different types of cancer. And while there are slightly more overweight and obese men than women, this is a big problem for women as weight is linked to breast and womb cancers.

Today’s figures estimate that breast cancer will remain the most common cancer in women over the next 20 years, and that womb cancer is climbing towards the top of the list too.

The rates of cancers linked to infection with certain forms of the human papillomavirus (HPV), such as anal and oral cancers, are also among the fastest growing challenges.

We hope the figures are an over-estimate: the full benefits of the HPV vaccine programme for girls have yet to be realised. But today’s projections show that now is not a time to be complacent about controlling HPV. Policy makers must ensure girls are being vaccinated and – if evidence shows it’s cost-effective – boys too.

So what about men?

Despite the fact that women’s cancer rates will accelerate, by 2035 they still aren’t expected to be as high as for men, who will have almost 27,000 more cases.

This partly reflects the fact that men still smoke more, and are more likely to be obese than women, but there could be other explanations too.

What can be done?

Today’s figures show that cancer is primarily a disease of old age.

As more people live longer, more people will get cancer. And there isn’t much that can be done about that – although they can be given the best chance of survival through earlier diagnosis and access to treatments.

But, as we mentioned, there are ways we can stop cancer cases reaching the predicted 500,000 a year. Around four out of 10 cancers are preventable. And these latest projections reinforce that point, showing where the biggest challenges are likely to come from in the future.

Ditching the cigarettes, cutting down on alcohol, eating a balanced diet and exercising more are changes we can all make to live healthier lives and reduce our risk of getting cancer.

But the Government needs to make changes too, such as protecting children from being bombarded by junk food advertising, and ensuring smokers have access to high quality Stop Smoking Services.

So whether it’s cases or rates, we all have some control over how right, or wrong, today’s forecasts might prove to be.

Rebecca Smittenaar is a data analysis and research manager at Cancer Research UK

Reference

Smittenaar, C., Petersen, K., Stewart, K., & Moitt, N. (2016). Cancer incidence and mortality projections in the UK until 2035. British Journal of Cancer. DOI: 10.1038/bjc.2016.304