Lymphoreticular malignancies as environmental disorders

Abstract

Information of considerable importance has been gained from comparisons of the incidence of various malignant diseases, both between and within various populations. Although the role of hereditary factors can never be completely excluded, it is likely that the vast majority of the geographic differences observed for most cancers are environmentally induced. This would also appear to be true of the lymphomas and leukaemias, which are characterised by markedly diverse international patterns. When differences in incidence are polarised to the extent that a disease occurs only or mainly in relatively circumscribed areas, as is true with Burkitt’s lymphoma, this allows one to concentrate on the differences between regions of high and low incidence. Do these areas differ mainly with respect to their physical environment (e.g. climate, geology), biologic environment or both? It must be realised, however, that it is difficult to dissect man from his environment; just as the nutritional, hygienic and socio-economic standards set by man can alter his environment so too existing physical and biologic factors can dramatically affect his activities. Despite all its uses, geographic epidemiology has its limitations, largely due to the lack of suitable statistics from certain areas, especially more primitive ones, and under ascertainment of cases which may be a function of the diagnostic facilities available. It is therefore imperative that other methods be employed in evaluating the possibility that a disease is environmentally induced. These include time—space cluster analysis, migration studies and evaluation of peculiar situations such as familial aggregations of a disease. Again each method has its own limitations so that a variety of approaches must be taken to adequately evaluate this question. This chapter examines the evidence that environmental factors might be important in the aetiology of certain lymphoreticular disorders.