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| Cancer prevention | Radiations and environment | |
Environment
According to many evaluations, around 2% of cancers could be due to environmental causes, but these figures are very approximate, are not backed by any rigorous scientific data and are probably an underestimation of the reality. However, certain claims of great numbers of environmental cancers are also totally void of any scientific epidemiological or biological proof (such as DNA modifications).
The majority of declarations about the ‘appalling” role of atmospheric pollution are mainly related to respiratory diseases (child asthma) or allergies (eczema) but not necessarily cancer.
Unfortunately, (except perhaps as the consequence of a catastrophic event like the Tchernobyl explosion), we may well be unable to prove the role of pollution or environmental factors due to the major toxicity of tobacco and alcohol and their broad use by the earth’s inhabitants.
Sun radiations
Sun is the most important source of ionising radiation by ultraviolet rays.
The majority of the sun’s dangerous rays are captured by the earth’s atmosphere, in particular by the stratospheric ozone layer: cosmic rays, gamma rays, X rays and ultraviolet C rays. The ozone layer only allows rays with a wavelength above 290 nm to pass through.
It is established that holes in the ozone layer are dangerous since they diminish protection against the sun’s rays. However, their apparition is not responsible for the increasing number of skin cancers, since they are mainly observed in areas of low population density. . Interestingly, the reduction of the use of PFC gas is beginning to reduce the formation of holes in the ozone layer.
The increased risk of skin cancer would appear to be correlated to an increase in sunbathing and the overwhelming desire to obtain a good tan without sufficient skin protection. Water reverberation on the sea, snow or ice are further aggressions to our skin, exacerbated by the fact that the cooling effect of the wind or winter temperatures tend to lead us to forget the ever-present burning effect of the sun. Ultraviolet rays are responsible for two types of skin cancer:
- epidermal carcinoma (either basal cell carcinoma or spinal cell carcinoma) which is the most frequent but is generally not dangerous if treated early,
- melanoma (5 - 6,000 new patients in France each year), for which early diagnosis (or systematic screening) and complete removal are the only guarantees of cure.
Epidermal cancers generally affect older people or workers who are regularly exposed to the sun, like farmers and fishermen. The most affected parts of the body are those exposed to the sun on a daily basis, for example the face and the chest. Surgical removal or local contact radiotherapy are very efficient. Spinal cell carcinoma, in rare neglected cases, may metastase and become lethal.
On the contrary, melanomas mainly affect young people, originating in usually unexposed parts of the body (only exposed during sunbathing or surfing for example). People with a blond complexion are at particular risk since they produce less melanin than those with a darker complexion. Therefore, Australians who often have a clear blond complexion (or are red-headed), live in a very sunny climate at equatorial latitudes and are very keen on beach sports, are at great risk, with the highest incidence in the world.
Hereditary diseases
A few particular hereditary diseases predispose to more or less generalised skin cancers :
Prevention of skin cancers consists:
- in educating the general public on the potential dangers of the sun, of
prolonged sunbathing and the regular examination of moles(nevus).
- in educating physicians (notably general practitioners) and other carers
on the regular examination of their patients’ entire skin, insisting
that they be very precise in their diagnosis (using ABCDE rules for melanoma)
- in the regular use of protection against the sun’s rays: spontaneous protection (in French) or use of protecting sun cream (in French).
The respect of such very simple preventive measures should result in a significant reduction in the number of already metastatic melanomas, for which treatment is nowadays purely palliative.
Many very interesting sites (notably from Australia) are dedicated to the prevention of melanoma:
Sun Safety SunSmart
Ionizing radiations
We are all subject to natural irradiation to which human activity adds some artificial irradiation sources.
Face workers' are exposed to relatively important irradiation levels. Uranium miners undergo specific medical control.
The main artificial source of irradiation is provoked by physicians through numerous radiological examinations. Thus, as physicians, we should limit our requests to only those examinations offering the quickest and easiest diagnosis, if essential for the patient. Every radiological examination is a disturbance for patients.
Great precaution should be taken to protect doctors and technicians working in radiology units. In the past, we observed many skin tumours induced by excessive exposure to radiation (for instance surgeons reducing a fracture under radioscopy). Leukaemia and sarcomas were also observed.
The effects of the massive irradiation in Hiroshima and Nagasaki during the second world war has been intensely studied by the American military authorities (see also the study by some Yale students)
The nuclear industry has brought many precautionary measures such as individual surveillance of employees, regular studies of radioactive waste and its potential effect on the surrounding population. (In France, for instance, a dedicated tumour registry has been created in the Manche Department in order to study the potential harm caused by the La Hague recycling nuclear fuel facility). Such prevention of nuclear accidents, and regular training to ensure procedure observance are absolutely necessary.
The Tchernobyl accident (in French) clearly demonstrated how the combination of human failure, poor technical conception and the absence of training for efficient crisis reaction can result in catastrophic situations.
One of the solutions to prevent the risk of thyroid carcinoma (as observed around the Tchernobyl area) is the quick absorption of iodine potassium capsules. Many iodine capsules have been distributed to the French population living around nuclear plants. Their efficiency has been demonstrated (due to the iodine saturation of the thyroid gland). However its practical efficiency may be dubious since such measures should be applied at the very onset of radioactive rejection. Repeated exercises are necessary to ensure that the population correctly apply such measures, however authorities are reluctant to insist on or even suggest the potential danger in living close to a nuclear plant.
Another source of irradiation is frequent high altitude travel by plane. During flights, pilots, cabin crew and passengers are exposed to cosmic rays without the usual ozone filter. Most rays are neutrons and gamma rays. Annual doses around 2 to 5 mSv are quite frequent (and notably for the staff of Concord or those travelling above the polar zones). However, the real impact for flight personal is difficult to evaluate, due to the low number of subjects involved, but also due to other toxic or dangerous habits such as frequent smoking and solar exposure during stopovers.
The irradiation of astronauts during space flight should also be considered and studied.
The difficulty in studying the precise role of small doses of irradiation is noteworthy. In the past, certain authors considered that a small amount of irradiation might stimulate immunity and DNA repair mechanisms. A precise exposure threshold is difficult to define and for this reason systematic precautionary measures should be taken for all potentially exposed personnel.
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