Are cancers a modern phenomenon?

Yesterday, I came across a news report on a study by Professor Rosalie David and Professor Michael Zimmerman of the University of Manchester, who postulate that cancers are in large part a modern phenomenon and are ‘man-made’. I have objections to almost all of the claims the researchers make, so I will address them one by one.

Tumours were rare until recent times when pollution and poor diet became issues, the review of mummies, fossils and classical literature found.

It is true that there are more contaminants in the environment and poor lifestyle choices has led to an increase in some types of cancers. Numerous studies have shown pollution to be a factor in cancer, albeit a minor one. Inactivity, excess body fat, heavy drinking, and smoking are well known to increase your risk of developing cancer.

However, the main reason for the rarity of cancer in the past is that people lived much shorter lives. The chances of development many forms of cancer increases with age. Improvements in healthcare mean we are living much longer than past generations. Most cancers occur in individuals over the age of 50, well beyond the expected lifespan for much of human history. The increased detection of cancer is also due to our improved capacity to diagnose cancers.

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 industrialisation.

All animals get cancer. Even sharks! There is no reason to think that our ancestors were any different.

The authors find that there is a low prevalence of cancers which are already rare for the age group under examination. In a different study, Zink and colleagues observed 4 cases of malignant tumours in a series of 325 Egyptian mummies. It is reasonable to assume that these numbers represent a minimum, given the limitations of diagnosing cancer in ancient tissues.

These and other studies show that cancers did occur in Egyptian mummies. How then do the authors get from cancers occurred in ancient populations to cancers are the product of modern industrialisation?

Dismissing the argument that the ancient Egyptians didn’t live long enough to develop cancer, the researchers pointed out that other age-related disease such as hardening of the arteries and brittle bones died [sic] occur.

The authors of this study conveniently choose to dismiss perhaps the most important predictor of most cancers – age. The study looked at mummies between the ages of 25 and 50, although people over the age of 50 are by far at greatest risk of getting cancer. According to a 2010 American Cancer Association report [pdf] around 78% of cancers are diagnosed in people 55 years and older. A primary reason many cancers are on the increase is because people are living longer. Given the short lifespan of prehistoric people it is inevitable that the occurrence of cancers will be much greater today.

Even the study of thousands of Neanderthal bones has provided only one example of a possible cancer.

The one example the authors refer to is the Stetten II skull bone, believed to date to 35,000 years BP (before present). There a tumour on the parietal bone of this specimen. However, much of the Stetten material has been redated to less than 5000 years BP, including a cranium designated Stetten II.

What’s more, the authors fail to mention the Ferrassie Neandertal, whose leg bone lesions have been interpreted as possibly being the result of lung cancer. This specimen has bilateral periostitis, which is a common manifestation of hypertrophic pulmonary osteoarthropathy (HPO). HPO is a condition associated with a number of circulatory and lung diseases. Among the most common causes of HPO are pulmonary carcinomas. Palaeopathology is a tricky business in which practitioners attempt to reconstruct past diseases and infections from often ambiguous marks left on the bones. While the Ferrassie case is open to interpretation, it should not be dismissed out of hand.

It is also worth noting that the incidence of bone cancers are incredibly low. Moreover, osteosarcomas affect mostly children. Bone cancers are among the rarest types of cancer. The number of new cases of bone cancer in the US so far this year is 2,650. To put this into perspective that’s 0.000009% of the US population that have been diagnosed with bone cancer in the last year. Other cancers may secondarily affect bony tissue but, like the Ferrassie Neandertal above, the aetiology in such cases is more equivocal.

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.

The ascertain that nothing in the environment causes cancer is demonstrably wrong. Prolonged exposure to UV rays is the chief cause of skin cancers. Human papillomaviruses and hepatitis viruses cause cervical and liver cancers respectively. Helicobacter pylori bacteria have been linked to gastric cancer. Exposure to radon is the second leading cause of lung cancer (after smoking), while carcinogenic aflatoxins are made naturally by moulds.

In conclusion, the researchers found only a few cases of cancer in a relatively small sample of mummies. These mummies were all estimated to be 50 years of age or younger – a demographic with a relatively low risk of cancer. Added to this, it is likely that the true rate of cancer was much higher than what was possible to diagnose for these ancient and somewhat degraded specimens. While it is interesting to ask how prevalent cancers were in the past, this study does little to shed light on the answer.

References

Fennell and Trinkaus (1997). Bilateral femoral and tibial periostitis in the La Ferrassie 1 Neanderthal. Journal of Archaeological Science. 24 (11) pp. 985-995.

Rosalie David and Zimmerman (2010). Cancer: an old disease, a new disease or something in between? Nature Reviews Cancer 10, 728-733.

Zink, Rohrbach, Szeimies, Hagedor, Haas, Weyss, Bachmeier and Nerlich (1999). Malignant tumors in an ancient Egyptian population. Anticancer research. 19 (5B):4273-7.

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