Cancers from 250 million years ago

There is evidence to suggest that people in a particular part of China are dying today from cancers that owe their origin to something that happened 250 million years ago.

It is generally accepted today that a mass extinction of species – notably but not exclusively the dinosaurs – happened about 65 million years ago. However, that is only one of several occasions on which the development of life on Earth was thrown out of kilter by a devastating event that was almost literally earthshattering. These events appear to have been caused either by the impact of a large extra-terrestrial body, such as a comet or an asteroid, or a massive volcanic event. Sometimes both seem to have happened at roughly the same time.

About 250 million years ago a vast amount of lava poured on to the Earth’s surface in what is now Siberia. The flows occurred over a period of around a million years, covered an area of more than 2.75 million square miles, and amounted to more than half a million cubic miles of material. This flow marked the end of the Permian period of geological history and ushered in the Triassic.

It is also conjectured that a large piece of space rock, probably several kilometres across, hit Earth at around this time in what is now Antarctica. This formed what is known as the Wilkes Land crater, which can only be seen by analyzing seismic and gravity data due to being buried deep under the Antarctic ice cap.

It has also been suggested that the asteroid impact could have caused the lava output by, in effect, cracking open the Earth’s crust. However, this theory is highly speculative and is not universally accepted.

The net result was that the planet suddenly became a very difficult place on which to live, due to the vast quantities of noxious volcanic gas that would have been belched out into the atmosphere. An asteroid impact would also have produced so much dust that the Sun would have been shielded for many years leading to plant life being severely affected. It is thought that some 96% of marine species and 70% of land vertebrate species became extinct. It could have taken as much as 10 million years for animal life to recover.

But what has all this to do with the prevalence of cancer in China?

The volcanic gases mentioned above would have caused the rain that fell to be highly acidic. This in turn would have worn away the rock it fell on in the same way that acid rain today wears away the stonework of buildings. The rainwater would have become very rich in silica, which comes from the grains of sand worn from the bedrock.

In what is now Xuanwei County in China’s Yunnan province the silica-rich water would have become the groundwater in an area of lush humid forest, which was doomed to decline due to the difficulties mentioned above. The forest would in any case have been sitting on a deep layer of peaty soil formed from many generations of growth. This peat would now be impregnated with large quantities of silica.

After millions of years of consolidation and pressure peat turns to coal, which now underlies Xuanwei County. It is this coal that is mined and burned by the local people, but it is coal that is unusually rich in silica, and the silica is blamed for causing the extra cancers.

How it does this is a matter for debate. It could be that the silica is released into the air that people breathe, and silica is a known carcinogen. Or it could be that coal fumes, which are also carcinogenic, could be made more dangerous by the silica. Or possibly both factors are at play.

Coal is widely used as heating and cooking fuel throughout China, in exactly the same way that it is in Xuanwei County, so something must account for the fact that there are 20 times more cancer cases there than elsewhere, and that applies to both smokers and non-smokers.

So could what happened 250 million years ago have such dramatic consequences today? The jury is out, but it does seem possible.

© John Welford

Lung metastasis

Metastasis is the transfer of cancer from one organ or part of the body to another. Cancer cells are able to invade the bloodstream and end up virtually anywhere in the body. A lung metastasis is therefore a secondary cancer in the lung that has spread from somewhere else.

When metastasis occurs, the lungs are frequently the destination of cancer cells, and a lung metastasis is found in one third of all patients whose cancer proves to be fatal. It is often the discovery of a lung metastasis, as a result of investigating the causes of certain symptoms, that shows that the patient already has a tumour somewhere else in the body.

The lungs are organs the functions of which are closely linked with those of many other organs, such as in the transfer of oxygen and nutrients, but this leaves them vulnerable to secondary infections of many kinds coming from other organs. They are composed of sensitive tissue that is easily damaged. These two factors make metastasis to the lungs a common event.

The primary cancer can be virtually anywhere, but the cancers that most frequently spread to the lungs are those of the breast, colon, prostate and bladder. It is also possible for a lung metastasis to come from a primary lung cancer, but this is usually only after it has spread to another organ and then back to the lungs. A metastasis can be present in the lung in a dormant state long after the primary tumour has been removed and the patient has been thought to be clear of cancer.

Much research has been done to discover why cancers spread in this way. For example, research at the Howard Hughes Medical Institute in Chevy Chase, Maryland, has suggested that a group of four genes, working together, enables cancerous cells from breast tumours to escape into the bloodstream and cause lung metastases. Shutting off all four genes at the same time has had a dramatic effect on halting not only metastasis but also the growth of the original tumour. In all, the researchers have discovered 18 genes that make a contribution to metastasis, and they have also found that targeting the proteins produced by these genes, using drugs that are already on the market, could be effective in reducing metastasis.

Another possible breakthrough has been made at the Cold Spring Harbor

Laboratory, New York, where the cells have been identified that cause a dormant lung metastasis to become aggressive, often with fatal results. These are endothelial progenitor cells, or EPCs, and they are found in the bone marrow. They provide the switch that leads to blood vessel development within a tumour, and hence its growth. Knowing the mechanism involved is a huge step forward in devising treatments that could save many lives.

The symptoms of a lung metastasis include shortness of breath, chest pain, coughing, unexplained weight loss and general weakness, all of which can be symptoms of other conditions, some of them much less serious. It is also possible for there to be no symptoms at all, and for the metastasis to be revealed during other procedures, such as a chest x-ray for another purpose.

Treatment for a lung metastasis is usually chemotherapy, as surgical removal does not guarantee that all secondary growths have been treated. As the patient’s cancer is likely to be at an advanced stage, major surgery may not be advisable in terms of the patient’s general condition. However, surgery can be an option under certain circumstances, for example when there is a good chance that all the tumours have been detected and can be removed. As mentioned above, current research provides hope of new treatments becoming available in the foreseeable future.

© John Welford