World cancer patterns / Sharon Whelan

world cancer patterns Cancers can take many years to develop, so it will take time to learn how to prevent them. The International Agency for Research on Cancer is committed to this task Sharon Whelan T he number of cancer deaths a relatively modern disease, but while it worldwide has been calcu- is true that the investment needed lated to be about four mil- today for its control is great and lion each year, while over six liable to increase in the future, there million new cases of cancer is evidence that the disease has are diagnosed annually. The world been around from pre-historic times. population is about 5,000 million, of Tumours have been reported in the whom some three-quarters live in fosilised remains of a dinosaur, and in developing countries. Since the the dorsal vertebrae of a cretaceous number of cancer cases is about the mosasaur (a large lizard). The femur of same in the developing and the a Homo Erectus ("Java Man") was developed countries, it follows that the found to have a probable tumour, and levels are proportionately higher in the the Ebers papyrus from the Nile Valley, latter. Cancer is - broadly speaking - a dating back 3,000 years, recorded disease of middle and old age, and the prescriptions for skin cancers. Ayurve- aging of the world population follow- ing the control of infectious and parasitic diseases will result, on demo- graphic grounds alone, in substantial increases in the cancer burden. While cancer of the lung is the commonest cancer in men and breast cancer the most frequent form in women in developed countries, cancer of the cervix is a major problem in the developing world, accounting for 24 per cent of all cancers in females. The increasing number of cancer patients leads us to think of cancer as die books from Ancient India, dating back some 2,500 years, describe tumours of the oral cavity, pharynx, oesophagus, pelvis and rectum; Hip- pocrates of Cos (around 460-380 BC) observed the spread of cancer within the body. In the 17th and 18th centuries, the revival of learning led to enquiry into the nature of the world by reasoning and through experiment throughout Europe. The first of such "epidemiolo- gical" observations related to cancer may be attributed to Bernardino Ramazzini (1633-1714 ), who reported an excess of breast cancer in nuns in Padua, and John Hill (1716-1788), who suggested that snuff was respon- sible for nasal cancer and polyps. In 1775, Percival Pott described cancer of the scrotum in chimney-sweeps - the first cancer to be linked to occupation. Research in the early 20th century showed links between (for example) cancer of the breast and age at marriage, between oral cancer and betel quid chewing in India, and between lung cancer and tobacco smoking. Cancer epidemiology as we know it today, however, probably started in 1950 - the year when studies on the association between lung cancer and smoking made news, and when an Oxford symposium on the geographical pathology and demo- graphy of cancer, held under the auspices of WHO and UNESCO, brought together much of the available know- ledge on cancer patterns. It became clear that there were factors in the Cancer has been around since the time of the dinosaurs. Below: Occupational hazards: /ARC is looking into the relationship between cancer, and those exposed to welding fumes. Photo WHO/ P. Larsen World cancer patterns 26 environment which could cause cancer, and it followed from this that removal of such factors - if only they could be identified - would prevent the disease. In 1963 a group of French scientists and thinkers suggested that the industrial nations should devote 0.5 per cent of their military budgets to research on cancer. The budget allo- cated to this project has never approached that optimistic objective, but there was sufficient interest to bring about the inauguration, two years later, of the International Agency for Research on Cancer (!ARC). Estab- lished in Lyon, France, the agency is an autonomous body within the frame- work of WHO; it started with five contributing nations, and 14 countries now participate in the control and financing of its activities. Since its inception, the overriding interest of the Agency has been the search for the causes of human cancers and the dissemination of information for their prevention. The efforts and resources of many national programmes have been concentrated on the curing of cancer, and it was decided that !ARC was uniquely placed to study the geographical and ethnic differences in cancer occurrence which can give clues to its aetiology. The systematic collection and analysis of data, which is the primary aim of descriptive epidemiology, and is one of the basic tasks undertaken by !ARC - is hampered even today by differences in the availability of medical resources, in terminology and in methods of diagnosis. However, the study of mortality statistics, of reliable incidence data from defined popu- lations and of pathology material and case series has confirmed that there are enormous differences in the occur- rence of many cancers both between different geographical areas of the world and among different ethnic and religious groups within the same area. Examination of data from all over the world shows that, among women, either breast cancer or cervical cancer is commonest in every region except the USSR, where stomach cancer heads the list. In men, there is greater variation in the top-ranking cancer site between different geographic regions: liver, bladder, lung, lymphoma, sto- mach, mouth/ pharynx and prostate all rank first in one region or another. Lung cancer is predominantly a cancer Mate drinker in the high Andes. Is there a link with high rates of oesophageal cancer? Photo Massino Crespi © WORLD HEALTH, June 1989 World cancer patterns of men in the developed countries, but is increasing among women in developed countries and in both sexes in developing countries. The next stage in the epidemiologi- cal process is an attempt to answer the question "Why?". The goal of !ARC is to identify the agents that cause this disease. It is generally agreed that up to 80 per cent of cancers are linked to our environment and our lifestyles: the problem is the multitude of potential risks which surround us and the fact that risk factors are different for different cancers. There may be a combination of elements creating a risk, or one risk factor can be magni- fied when combined with another. Alcohol and tobacco are individual agents implicated in the causation of cancer of the larynx: a recent study in south-western Europe shows that when both habits are combined the risk is significantly higher than for either alone. Potential cancer-causing factors in our environment range from sunlight through diet (including methods of preserving food) , tobacco consumption, occupation (resulting in exposure to chemicals, mineral fibres or dust), air and water pollution and inadequate hygiene. Cancer belt Cancer of the oesophagus makes an interesting example. There is an "oeso- phageal cancer belt," stretching from the shore of the Caspian Sea in Northern Iran through the southern republics of the USSR to western and northern China, where incidence rates in some areas are 200 times higher than those in most of the rest of the world. Incidence is also high in parts of eastern South America, and in a part of northern France. Increased inci- dence is likely to be due to a combin- ation of dark tobacco and distilled alcoholic drinks in Brittany, France, to opium products on the Caspian shore, and to other less well identified causes in China. In Latin America, the highest rates of oesophageal cancer are observed in parts of southern Brazil, Uruguay and north-eastern Argentina. About 80 per cent of the population drink a hot infusion called mate, and studies are being carried out to assess whether there is more of this cancer among the mate drinkers, and if so whether this is due to thermal injury (since it is drunk very hot) or to the chemical nature of the infusion. Within !ARC, in addition to studies on diet, alcohol and tobacco, the work environment is under investigation. Cancer risks in workers in the herbi- cide production industry and those exposed to welding fumes are being WORLD HEALTH, June 1989 examined; exposure to silica has been investigated in relation to lung cancer. Viruses are also under scrutiny; for example, the role of the human papil- loma virus in cervix uteri cancer is being examined in Spain and Colom- bia. Genetic predisposition to cancer is another line of inquiry, in the hope of identifying high risk groups of individ- uals. A survey of childhood leukaemia over a 15-year period in Europe will describe variations in incidence, in particular to see whether changes observed can be related to exposure to radioactive material from the accident at the Chernobyl nuclear power station in the USSR in 1986. We are still smoking As with many cancers, lung cancer can develop 20 years or more after initial exposure to the risk factor. The very high levels in industrialised coun- tries reflect the substantial increase in per capita consumption of cigarettes since the first World War. Following biomedical evidence that correlates lung cancer in non-smokers with their level of exposure to other people's smoking, an international study of lung cancer in non-smokers has been started. Despite the large body of evidence proving the role of tobacco in lung cancer, we are still smoking - and allowing publicity to attract young people to the smoking habit. This indicates that epidemiological mes- sages by themselves are not enough! Three-quarters of the total number of liver cancers in the world (250,000 new cases a year) occur in the developing countries. High-incidence areas include sub-Saharan Africa, East and South-East Asia (as far west as Burma) and Melanesia. This geogra- phical distribution of liver cancer shows a close correlation with the prevalence of chronic carriers of hepatitis-B. A study has started in Gambia to evalu- ate the effectiveness of hepatitis-B virus vaccination in preventing chronic liver disease and primary liver cancer in a population at high risk. Since cancers can take many years to develop, it will also take time to learn how to prevent them. So this project is designed to last for 40 years. Epidemiological research, particu- larly when linked with laboratory services, can contribute to our under- standing of the mechanisms of cancer. No sudden breakthrough is going to show us, overnight, how to eliminate the multitude of risk factors in our environment. But the patient work of years in many disciplines will guide us on the first steps towards the ultimate purpose of !ARC: the prevention of cancer. • The Challenge of Epidemiology Epidemiology has a long history, and those who study it would often like to know "where this idea came from?" and "why this was said in such a way?" The Pan American Health Organization (PAHO) . which functions as WHO's Regional Office of the Americas (AMRO). req~ntly published a selection of the most important texts in epi- demiology. These were chosen by consensus among noted · practitioners of the science, all · over the world. with comments by four senior epidemiologists froxn the Region of the Americas. The five parts of the bdok cover historical development (11 texts). transition from old to new epidemiology (7 texts). investi- gation of causes (48 texts). and health services and health poli- cies (13 texts). lt ends with a discussion of future trends. Although the selections tend to be rather heavily slanted towards the Anglo-Saxon world. they include texts originally written in languages ranging from Greek and Russian to Japanese. and they cover the worldwide range of problems which present-day epidemiology addresses. The discussions (apparently verbatim records) are refreshingly informal and provide an insight into the workings of the epidemiological mind. The Challenge of Epidemio- logy, a blockbuster of over 1 000 pages. is available in English and Spanish. and may be ordered from Pub lications. AM RO/ PAHO. 525 23rd Street. N.W .. Washington. D.C .. 20037. USA. Anyone with an interest in how epidemiology affects our daily health and the way we perceive health and disease should find plenty to interest tQem in these pages. Is he growing fast enough? Data-coOection in Argentina. Photo Dlana Surraco Medus de Molinas 27