The link between obesity and a record rise in cases of kidney cancer was widely covered by the news media today. “Bigger waistlines linked to rise in kidney cancer,” said The Independent, while the Daily Mail reported that the number of new kidney cancer cases was three times higher than in 1975.
The stories come from new figures released by Cancer Research UK, which show that the number of new cases of kidney cancer diagnosed each year in the UK has, for the first time, risen to more than 9,000, up from just under 3,000 in 1975. This makes kidney cancer the eighth most common cancer in the UK.
The charity says that some of this increase could be due to the greater use of imaging techniques helping to diagnose more kidney tumours.
However, rising obesity levels are also a factor. After smoking, obesity is one of the main risk factors for kidney cancer, with research suggesting it increases the risk by 70%.
What do the new figures show?
The new figures show that in 2009 there were 9,286 new cases of kidney cancer in the UK – 5,706 (61%) in men and 3,580 (39%) in women. This rate represents about 19 new kidney cancer cases for every 100,000 men in the UK and more than 11 new cases for every 100,000 women.
Cases of kidney cancer have steadily increased in the UK since the mid 1970s, when numbers of new cases were just under 3,000. Kidney cancer is now the sixth most common cancer in men and the ninth most common cancer in women.
Among women, rates are significantly higher in Wales and Scotland, compared with England. However, the new figures show a narrowing of the north-south divide in kidney cancer incidence, which has existed since the 1990s, with many areas across England showing rises.
Kidney cancer is also strongly related to age, with an average 62% of cases diagnosed in people aged 65 years and over.
What has caused the rise?
The rise is believed to be partly due to more widespread use of imaging techniques such as ultrasound and computed tomography (CT). This has led to more cases of the disease being picked up before symptoms appear, when people are being examined for other reasons.
However, Cancer Research UK says there has also been a rise in the number of advanced kidney cancer cases being diagnosed, suggesting that other factors, in particular rising levels of obesity, are involved.
There appears to have been no new research investigating this potential association, but Europe-wide analysis of studies published between 1966 and 1998 found that the risk of kidney cancer increased by 7% for each unit increase of body mass index (BMI). This means people who are overweight have a 35% higher risk of developing kidney cancer than those with a normal BMI. This rises to 70% in those who are obese.
Cancer Research UK’s figures estimate that about 25% of kidney cancer cases in men and 22% in women are linked to being overweight. Overweight people produce higher levels of certain hormones than people of a healthy weight, and this may contribute to an increased risk of several types of cancer, including kidney cancer.
Smoking is the other main lifestyle risk factor for kidney cancer, but the charity points out that smoking rates have fallen in the last 35 years while obesity is on the rise. In the UK, figures show that nearly 70% of men and almost 60% of women have a BMI of 25 or more, meaning they are classed as overweight.
How does the UK compare to other countries?
Kidney cancer incidence rates for the UK are estimated to be the 14th highest in Europe for men and the 16th highest in Europe for women. The highest rates for 2008 were in the Czech Republic for both sexes, with the lowest rates in Cyprus for men and in Malta for women. Worldwide, cancer incidence rates are highest in North America and lowest in Western Africa.
What is the best way to prevent kidney cancer?
While genetic factors play a role in the development of any cancer, including kidney cancer, smoking followed by obesity are the two main risk factors for the disease, in terms of lifestyle. Maintaining a healthy weight and not smoking are the best ways to cut the risk.
Sara Hiom, director of information at Cancer Research UK says: “Too few people know about the significant cancer risks associated with being very overweight. While giving up smoking remains the best way to cut your chances of developing kidney cancer, the importance of keeping a healthy weight shouldn’t be overlooked. Obesity is not only linked to kidney cancer but six other types of cancer and other diseases as well.”
What else can I do?
Blood in the urine can be an early sign of both kidney and bladder cancer. Although people with this symptom may not have cancer, it is important that anyone who experiences it sees their doctor as soon as possible. Specialists say that if kidney cancer is caught early it has a good chance of being cured by surgery, while the development of new drugs that destroy the blood supply to kidney tumours can now control the disease.