The Gazette 1990

GAZETTE

JANUARY/FEBRUARY 1990

Lung Cancer The term lung cancer is now used by respirologists and other clinicians to refer to what is pathologically correctly termed "carcinoma of the bronchus" (in other words not all cancers of the lung are what is colloquially known as lung cancer). This cancer is in fact a cancer of the lining of the bronchial tubes. As it grows it breaks through the walls of the bronchial tubes and becomes the ugly white mess so characteristic of x-rays of lung cancer. A question which I tried to deal with in an earlier paper (Murphy, D. L., Journal of the National Industrial Safety Organisation, July 1985) was whether lung cancer could occur in an asbestos worker with no evidence of asbestosis. Professor Sir Richard Doll and Professor R. Peto in one of their reports on asbestos related disease to the British Health and Safety Executive, felt that it was unlikely that lung cancer in an asbestos worker who had no evidence of asbestosis was due to asbestos exposure. As I said previously, 50% of a population of asbestos workers finally died from lung cancer, not asbestosis. It is obvious from this that the lung cancer comes at a later stage. Occupational cancers in general have a latent period of between 20-24 years. This latent period is the period from first exposure to the cancer causing agent (carcino- gen) to diagnosis of the disease. Another general characteristic of cancer due to occupation is that it tends to occur at an earlier age than the same cancers normally appear in the general population. "Occupational cancars in ganaral hava a latant pariod of between 20-24 years." Masothalioma The lungs are surrounded by a membrane known as the pleura. This is often described, in popular medical articles, as the "cellophane wrapping" surrounding the lungs. A certain form of asbestos known as crocidolite or "blue asbestos" was known for many years before it was discovered, in about 1964, that most cases of this disease were due to exposure to crocidolite. Sadly, some of the early cases were in small black children who played on the slag heaps outside the

cause x-ray change but do not give rise to any disability whatsoever. The possibility of cancer of the throat has been considered as being associated with asbestos but never proven. I intend only to con- sider asbestosis itself, "ordinary" lung cancer, and mesothelioma. Asbestosis Asbestosis is a disease character- ised by scarring (fibrosis) of the spongy tissue or parenchyma of the lung. It is one of the pneumoconioses. The difference between asbestosis and other sorts of pneumoconiosis is very obvious to the respirologist, radiologist, or pathologist dealing with an in- dividual case, where the real skill in diagnosis comes is at the very early stages however. The very earliest x- ray changes come at the base of the lung and the very earliest clinically detectable change is crackles, or wet sounds, also at the base of the lung. Diagnosis at this early stage takes a great deal of skill and experience. The severity of any pneumoconiosis including asbestosis is proportional to the amount of exposure both in volume and in time and no one knows why some individuals become easily affected and some individuals never develop the disease. The disease may not commence in fact until after exposure has ceased. In one study workers who developed asbestosis developed it in ten to twenty years after about two years of exposure. The first symptom of asbestosis is breathlesshess. Here again other causes of breathless- ness may lead the individual not to consult his general practitioner, and again there may be further diag- nostic delays as an individual moves through the system. Finally, ten, twenty or thirty years after the period of exposure, the individual is seen by a specialist and told "you have an occupational disease due to exposure to asbestos". What is the likely outcome? A survey, finishing in 1963, showed that 50% of a population of asbestos workers who had died during the study period died of lung cancer. " In one study workers who developed asbestosis developed it in ten to twenty years after about two years of exposure."

m Dublin 1. Fully furnished offices available * Daily. Weekly Monthly. Yearly 'Secretarial Service. 'Typing. Photocopying. Telex. Facsimile 'Conference Room/ Meeting Room Hire 'Car Parking & Registered Address Facilities. PHONE 01-724911 or call to Abbey Houee. crocidolite mines in southern Africa. As in all epidemiological studies, estimates vary. On this side of the Atlantic it is considered that 75% of cases of mesotheli- oma are due to exposure to asbestos. In the United States at least one expert, Professor Irving Sellikof, feels that as many as 90% of mesotheliomata are due to exposure to asbestos and that this need not always be just crocidolite. Mesothelioma tends to kill more quickly than ordinary lung cancer. Multiple causes Looking at these three diseases we can now consider some of the problems which may be general to occupational diseases and occupa- tional cancers. A smoker has a risk of developing lung cancer nine times the average. An asbestos worker, exposed to the kind of dust levels that would have been experienced in the industry thirty to forty years ago, who is not a smoker, has five times the average risk of developing lung cancer. An asbestos worker who is also a smoker has fifty times the risk of developing lung cancer.. The well- known association between as- bestos and lung cancer and smoking and lung cancer has been measured. What cannot be measured and must await future cancer research is why one smoker develops lung cancer and another

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