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TIME TRENDS IN INCIDENCE OF HAEMATOLOGICAL MALIGNANCIES AND RELATED CONDITIONS

Possibly the most important and challenging aspects of the epidemiology of the haematological malignancies lie in the apparent changes in occurrence which have been noted over the last few decades. No other group of inter-related malignancies provide such a complex and intriguing pattern. These trends appear to be on-going and present challenges for haemato-oncologists, not least because their clinical burden will be constantly changing. They also present challenges in the areas of public health and health promotion for future policy settings; health economists and purchasers of health care will also have a close interest in these changes. Most of all the burden is upon the epidemiologists to interpret and try to predict what is happening now and will happen in the future. The haematological malignancies and precursor conditions do not readily lend themselves to investigation from routinely collected data sources such as cancer registrational schemes. In such registries, routine statistical output for contrasting conditions are, amazingly, often pooled to give suf®cient numbers to analyse and `interpret'. Thus chronic lymphocytic leukaemia (CLL) and acute lymphoblastic leukaemia (ALL) are put together as are `all lymphoid leukaemias', whilst non-Hodgkin's lymphoma (NHL) is rarely subdivided in a way modern lymphoma pathologists would approve. In addition, most routine registers do not collect data on pre-leukaemias or other borderline conditions. Much reliance has therefore to be placed on specialist studies based on novel collections of data or special interpretation of routinely collected registry data. Because of these limitations there have been relatively few attempts to conduct a review of modern secular trends using a diagnostic framework which equates to modern diagnostic interpretations. This review attempts to do so and highlights the problems of these approaches.