Keeping a healthy weight can help cut your risk of cancer.
Cancer rates in the UK have been steadily increasing over the last few decades, largely because people are living longer. Now, 1 in 2 of us born after 1960 will be diagnosed with cancer in our lifetime.
That’s the picture for all cancers combined. But look a little closer at the numbers for individual cancers and a more complicated picture emerges.
This is the case for kidney cancer.
In the UK, around 5,500 people were diagnosed with kidney cancer each year in the mid-1990s, but this has now more than doubled, hitting about 11,900 a year.
In part, this increase in cases reflects changes in the overall population over time. But worryingly, our projections of what future numbers may look like position kidney cancer rates as among the fastest growing.
There isn’t a clear answer to why this is the case, but some theories are starting to appear.
Kidney cancer usually comes in 1 of 2 forms: transitional cell carcinoma and renal cell carcinoma.
And when we look at the number of people diagnosed with each of these types over time the story becomes more interesting.
In England, cases of transitional cell carcinoma have stayed relatively stable over the last decade.
But the number of people diagnosed with renal cell carcinoma has risen. It now accounts for just over 8 in 10 kidney cancers.
There’s no clear answer why this pattern has emerged. But renal cell carcinoma is linked to smoking and obesity, offering a couple of avenues for further investigation.
So while understanding all the factors behind this surge isn’t an easy task, it may be that in some cases our lifestyle is catching up with us.
Setting the scene
It’s important to remember that not all cases of cancer are preventable.
As with most cancers, part of the rise in kidney cancer rates is down to an ageing population who are at a higher risk of developing the disease because genetic mistakes build up in cells over time, which can lead to cancer.
But some cases could be prevented.
There’s no doubt that smoking has left an indelible mark on world health. But according to our stats smoking can’t entirely explain the rising rates of kidney cancer because of other factors at play.
More and more, public health campaigns have highlighted the rising problem of obesity. And the UK Government’s childhood obesity plan, released last summer, outlined the epidemic that we are facing as a nation.
The International Agency for Research on Cancer (IARC) first reported the link between obesity and kidney cancer 15 years ago. And research since then has helped establish a stronger connection between the two.
So perhaps obesity offers a possible explanation for rising kidney cancer rates?
Almost 2 in 3 people in England are now overweight or obese, a record high.
So the rise in kidney cancer does reflect the surge we are seeing in obesity.
But to explain this link, we first need to try and understand what excess body fat might be doing to the kidneys.
Fuelling kidney cancer – what’s fat got to do with it?
Although we’re certain that obesity causes 13 types of cancer, research has yet to unravel the exact mechanisms at play.
This is what IARC’s Dr Mattias Johansson, and other researchers around the world, are determined to crack. And although his research is at an early stage he has some interesting ideas.
“Unpublished data from our group suggest that high levels of insulin in the body due to excess weight may be one of the drivers of kidney cancer,” he says.
Insulin is a hormone that helps break down carbohydrates and fats, and the kidneys help process this hormone in the body.
Excess weight can lead to cells becoming resistant to insulin, which can cause levels of the hormone to rise and cells to divide more rapidly.
Researchers think that an increase in insulin has an effect on another molecule too, called insulin-like growth factor-1 (IGF-1).
Some studies have shown that IGF-1 encourages kidney cell growth in the lab and in mice, potentially telling cells to divide, and in some cases, leading to cancer.
“Another interesting hypothesis is that sex hormones may play a role in kidney cancer, but there are still few studies on the topic,” says Johansson. Changes in sex hormones, such as oestrogen, have been linked with obesity, and studies suggest that they may influence risk of womb cancer.
In womb and breast cancer the theory is that having excess fat changes the levels of these hormones in your body. Fat cells can become the chief source of oestrogen in women after the menopause, leading to higher levels of this hormone that can tell cells to multiply faster, increasing the risk of cancer.
Although the exact mechanisms linking obesity to kidney cancer are still to be confirmed, researchers are also looking at large population studies to try and identify who could be more at risk, and by how much.
Similar to smoking, where damage to cells builds up over time and increases the risk of cancer, damage from carrying excess weight accumulates over a person’s lifetime. And the more excess weight people carry, the greater their risk.
It’s clear that people who have a higher BMI have a higher risk of developing kidney cancer. This has been demonstrated in numerous studies
– Dr Mattias Johansson, IARC
One study looking at men found that in relation to kidney cancer risk, fat might start to have an impact on health from an early age. Being overweight in late adolescence was associated with an increased risk of kidney cancer later in life.
Overall, whether or not weight in childhood or as a teenager is directly linked to cancer risk isn’t yet clear.
Some studies on kidney cancer have looked at how the amount of weight gained can effect cancer risk. The more weight gained, the higher the risk.
“It’s clear that people who have a higher BMI have a higher risk of developing kidney cancer. This has been demonstrated in numerous studies,” says Johansson.
“Someone who is obese has up to twice the risk compared to those who are healthy weight, making it one of the most important risk factors of kidney cancer.”
But even this can’t fully explain the rising rates.
If you look, you will find it
Part of the reason we’re seeing more kidney cancers being diagnosed is due to developments in detecting the disease through advances in research and technology. But that could be a double-edged sword.
Finding aggressive cancers earlier, when they’re easier to treat, is good news. And Professor Tim Eisen, a kidney cancer expert at the Cancer Research UK Cambridge Centre, explains why.
Improved and more frequent use of imaging technology means that we increasingly detect tumours much earlier than we used to do
– Professor Tim Eisen, Cancer Research UK
Like a lot of cancers, kidney cancer “usually starts as a slow growing mass. It enlarges over several years and, as it grows, becomes more aggressive and more likely to spread to other parts of the body.
“Improved and more frequent use of imaging technology means that we increasingly detect tumours much earlier than we used to do.”
Doctors often remove these tumours through surgery, or if the tumour is small and the patient has other medical problems, they may suggest keeping an eye on things.
Kidney cancer can also sometimes be found during routine tests for other diseases, before cancer symptoms appear. But it’s not always clear if these cancers need treatment.
This is called overdiagnosis, and its potential role in the rising rates of kidney cancer also remains unclear.
Overdiagnosis is something we’re learning more about as more cancers are diagnosed earlier.
It means finding a cancer that wouldn’t have caused any problems during the person’s lifetime. In other words, if left untreated, it wouldn’t have led to the person’s death. This can happen with some tumours because they are slow-growing and unlikely to become a major health issue.
So while early stage diagnosis of some tumours could be life-saving, in other cases, patients might receive unnecessary treatment for their slow-growing cancer.
What’s clear is that we need more research to tell apart cancers that need treatment from the ones that don’t.
So how can we reduce our risk?
Although not all kidney cancers are preventable, many could be.
Stopping smoking and keeping a healthy weight could spare thousands a life changing diagnosis.
That’s why we’ve developed the Ten Top Tips with Weight Concern to help people lose weight and keep it off.
These include simple ways to eat and drink more healthily and be more active, like choosing sugar-free drinks, watching portion sizes, and trying to hit 10,000 steps a day.
While there are lots of ways you can make your life healthier right now, we know this can be easier said than done. This is why both the food industry and the Government have a large role to play to make the healthy choice the easy choice.
That’s why government needs to continue funding Stop Smoking Services and keep momentum behind their planned tax on sugary drinks.
It’s clear that the trend in kidney cancer cases is one to watch. The number of cases has risen steeply in the last few decades, a trend that’s set to continue if we don’t all take action.
Stephanie McClellan is a senior science press officer at Cancer Research UK