We were concerned to see headlines in the media today claiming that scientists say cancer is ‘purely man-made’. This is not only scientifically incorrect, but misleading to the public and cancer patients.
Our lifestyles have a great impact on our chances of developing cancer – as we’ve said many times. But the evidence that’s being used to justify these latest headlines doesn’t in any way support the assertion that cancer is modern or man-made.
In this case, researchers compared modern cancer rates to what they assume cancer rates were in pre-industrial civilisations. And they conclude that the difference between the two mean that cancer is caused by modernisation. We think this is completely unwarranted assumption, for a number of reasons – chiefly that people in ancient times didn’t live as long as people do nowadays, and cancer is predominantly a disease of older people.
We spoke to our director of Cancer Information, Dr Lesley Walker to find out what she thought of the story:
So where has this story come from? And what are the real facts behind the headlines?
The source of the story
The story is based on this press release publicising an opinion piece in the scientific journal Nature Reviews Cancer by Professor Rosalie David and Professor Michael Zimmerman. Their article discusses evidence for the existence of cancer in ancient populations, including Greeks, Romans and Egyptians.
Several lines of evidence show that cancer was certainly around in these ancient civilisations, including evidence of bone tumours in skeletons, and in many written manuscripts that discuss the symptoms and treatment of diseases that are likely to be cancer.
The researchers don’t dispute this evidence. But they do argue that cancer in these ancient societies may have been rarer than previously thought, as they believe that some lumps in fossilised bones may actually be non-cancerous bone growths rather than tumours.
However, the accompanying press release claims that “The virtual absence of malignancies in mummies must be interpreted as indicating their rarity in antiquity, indicating that cancer causing factors are limited to societies affected by modern industrialization.”
This statement simply isn’t supported by the information available. There isn’t enough evidence presented in the article to make any kind of reliable calculations about cancer rates in ancient populations – and certainly not enough to make bold statements claiming that cancer is “purely man-made”.
Age is the major risk factor for cancer
The suggestion that cancer was rarer in ancient populations is not surprising at all. But it’s not just because of our modern lifestyles. It’s because we live longer today than at any point in history.
Hundreds or thousands of years ago, life expectancy was short. Many people died in middle age from infectious diseases, and death in childbirth or childhood was also common.
But we know that cancer is mainly a disease of the elderly – three quarters of cases diagnosed in people aged 60 and over, and more than a third (36 per cent) of cases in people aged 75 and over. So it’s not surprising that cancer was a rare event in populations where people were unlikely to make it past 40.
There are many natural causes of cancer
Perhaps the most concerning statement comes from Professor David, who says in the press release:
“There is nothing in the natural environment that can cause cancer. So it has to be a man-made disease, down to pollution and changes to our diet and lifestyle.”
This is simply untrue.
There are many naturally-occurring causes of cancer that have been around for thousands of years – if not longer. Here are just a few examples:
- The sun. Ultraviolet radiation from the sun is the single biggest cause of skin cancer worldwide.
- Bacteria and viruses. Infectious agents are responsible for up to one in ten cancers in the UK, and one in four cancers worldwide. This includes human papillomavirus (HPV), which causes cervical and other cancers; Epstein-Barr virus, which causes some types of lymphoma; and Helicobacter pylori, which grows in gone-off food and causes stomach cancer. One of the main reasons for the large drop in stomach cancer cases in the UK is due to the widespread availability of refrigerators, and better living conditions which lead to lower infection rates.
- Radon. Produced naturally from granite rocks, radon is a radioactive gas that is thought to cause between 3 and 14 per cent of all lung cancers worldwide, making it the second most important cause of lung cancer (after smoking) in many countries.
- Naturally –occurring chemicals. There are many chemicals found naturally in our foods, produced by moulds or plants, that can cause cancer. For example, aflatoxin – produced by a mould that grows on peanuts and grains - is a potent cause of cancer. It’s very rare in the UK, but a significant cause of liver cancer in some parts of Africa and Asia.
To sum up
While this report discusses cancer in ancient Egyptian, Greek and Roman societies, it doesn’t tell us anything whatsoever about the reasons behind today’s cancer rates.
In fact, cancer rates have only been reliably recorded in the UK (let alone elsewhere in the world) since the 1970s, and comparing today’s worldwide rates with ancient descriptions of ‘illnesses that might have been cancer’, in an age where people tended to die much younger than we do, paints an incredibly misleading picture.
It can be tempting to worry about our cancer risk from external things like pollution and chemicals more than from things we can control, like our lifestyles. But decades of research have shown that lifestyle factors - such as not smoking, keeping a healthy weight, limiting alcohol, getting enough exercise and avoiding sunburn - have an important effect on cancer risk.
In contrast, the evidence that pollution and industrialisation has a widespread role in UK cancer rates is weak.
Claims that cancer is ‘purely man-made’ are confusing and misleading, and certainly don’t reflect the huge amount of scientific evidence piling up about the true causes of this devastating disease.
- New Scientist: Briefing on the story
- Cancer Research UK website: A brief history of cancer
- On this blog: Cancer ‘did not cause dinosaur extinction’
- The American Cancer Society: History of cancer – an in-depth look at cancer through history