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A Mummy

Cancer is rare in mummies, but it doesn’t mean the disease is entirely modern.

Appropriately enough as Hallowe’en draws near, the media are being stalked by a story about mummies and skeletons. We’ve already discussed last week’s misleading headlines claiming that ‘cancer is a man-made disease’, and today the story comes back to life in the Daily Mail.

Professor Rosalie David – the Egyptologist whose opinion piece published in Nature Reviews Cancer last week sparked the controversial headlines – has written a piece for the Daily Mail expanding on her ideas.

She argues that because evidence of cancer is very rare in ancient human remains, the disease must be entirely due to “modern, man-made” causes – including stress, poor diet, and pollution. But, as we pointed out before, looking for evidence of cancer in ancient Egyptian, Greek and Roman societies doesn’t tell us anything about the reasons behind today’s cancer rates.

Professor David is right that our lifestyles have an important impact on our chances of developing cancer, and that rates of cancer are increasing.  Large scientific studies have shown that smoking, diet, alcohol, and bodyweight can all affect our cancer risk. But to suggest that it’s an entirely modern disease, and to include stress amongst its major causes, is not borne out by the evidence in hand.

The causes of cancer are many and varied – the lifestyle factors mentioned above, our genetic makeup, natural cancer-causing agents such as the sun or viruses and the gradual accumulation of mistakes in our DNA throughout a lifetime all play a role.

Age is a major factor

The suggestion that cancer was rarer in ancient populations is not surprising at all. But there are a wide range of reasons for this. As we said last week, we live longer today than at any point in history – and 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.

In the Daily Mail article, Professor David points out that ancient human remains show signs of other diseases of ageing, such as osteoarthritis and artery hardening. But these diseases usually start setting in at a younger age than cancer.

We also have no hard evidence about the ages of these people when they died, so it’s difficult to draw firm conclusions.  Any cancer statistician worth their salt would demand to see age standardisation data from any population, whether alive or dead, before making statements about the numbers of people that might be expected to have cancer. We simply don’t have those data in this case.

Rare does not mean non-existent

Cancer is not a new disease, and it is not restricted to modern humanity. A study comparing cancer rates in fossilised dinosaur bones to those in ‘modern’ birds found no significant difference between the two – so it was certainly around a long time before civilisation.

In fact, it’s not surprising at all that signs of cancer are rare in human remains.  As we’ve mentioned, most people would have died from other causes before an age where cancer became a major issue. And out of those who did die with cancer, we would only expect a small proportion of their remains to be preserved. Finally, even for the people who did die of cancer, we wouldn’t necessarily expect to find evidence of it in those remains.

This is because tumours that start in the bone are relatively uncommon, and not all cancers spread to the bones. Most cancers start in soft tissues of the body, which usually aren’t preserved. So we wouldn’t expect to find many identifiable traces of the disease in skeletons – even after looking at thousands of samples.

What about mummies?

Much research has also been done looking for signs of cancer in mummies. The fact that Professor David’s colleague, Professor Michael Zimmerman has found hard evidence of a bowel tumour in a mummy may actually suggest that cancer was certainly around in the population – taking into account the relatively young age at which people died and how few mummies have been preserved, relative to the millions of people who must have lived through that time.

Scientists have also found evidence of a rare type of tumour in the mummy of a child from Chile. The fact that even one child mummy has been found with cancer – out of all the thousands of children who must have died at that time – actually tells us that cancer rates might not have changed all that much since ancient times.

And finally, there are many medical writings from ancient history that discuss cancer, or cancer-like diseases. Both ancient Greek and Egyptian doctors – including Hippocrates – wrote about how to diagnose and treat cancer, including using primitive surgery and herbs. It’s unlikely that they would have gone to this effort for a disease that was so rare as to be practically non-existent.

Lifestyle, stress and cancer

There are many naturally-occurring causes of cancer that have been around for thousands of years – if not longer, including UV radiation from the sun; bacteria and viruses (which cause a fifth of all cancers worldwide); naturally-occurring radon gas produced by granite rocks; and natural chemicals produced by plants and moulds.

Let’s also not forget that life was tough for most people in the ancient world. For example, cooking over open fires in enclosed spaces would expose people to carcinogenic smoke. We know that this is still a cause of lung cancer in parts of the world that still cook in this way, and it’s unlikely to have changed over thousands of years. Indeed, better ventilation methods in the modern world have probably reduced the number of cancers caused by cooking smoke.

In her article, Professor David specifically points the finger at “stress” as a major cause of cancer in the modern world.  But as we point out in the ‘Cancer controversies’ pages of our website, there is no solid evidence from robust scientific studies that stress leads to an increased risk of cancer.

However, stress might have an effect on our risk of disease by leading people into unhealthy behaviours, such as smoking and drinking – which we know can definitely increase cancer risk. But stress itself is not currently known to be a major cancer risk.

So there are many things out there that can cause cancer, and they have always been with us. But – as we’ve made clear – most people would have died of other causes before cancer claimed them.

The real causes of cancer

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 our alcohol intake, getting enough exercise and avoiding sunburn – have an important effect on cancer risk. In contrast, the evidence that pollution, stress and ‘industrialisation’ has a widespread role in UK cancer rates is weak.

Claims that cancer is ‘purely man-made’, based on an interpretation of a relatively small number of ancient remains, 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.

Kat

Further reading:

Comments

Simon, London October 25, 2010

Thanks for keeping up the pressure on this story.

I remain troubled as to how this paper got through peer review. Their methodology and data may have been flawless, but their extrapolation to the modern population produced a wholly untenable conclusion; David went on to demonstrate a lack of basic knowledge about carcinogenesis in her widely-reported statement in the accompanying press release. Was it peer-reviewed by paleopathologists rather than cancer experts, or did the reviewers allow a less-than-rigorously-supported conclusion because it was ‘only’ an opinion piece?

But then Nature also published Jacques Benveniste’s surprising results on extreme dilutions, although they did publish that with a disclaimer before going on to rubbish it the next month!

Ragnar Eriksson October 22, 2010

Very well written indeed. I am stunned that more people don’t turn to organisations like Cancer Research Uk for cancer information, with all the academics and scientists you have reviewing the data and research that has been compiled thus far, about this disease. It is sad to see people being swept up by media hype. Thanks for all the good work that you and your organisation do.