[The epidemiology and risk factors, in particular environmental, of malignant non-Hodgkin's lymphomas. The Working Group on the Epidemiology of Tumors of the Hemo- and Lymphopoietic Systems in Italy].

Malignant non-Hodgkin's lymphomas (NHL) represent a category of neoplasms that includes several types of tumours with different hystological and clinical characteristics. No large differences exist in incidence and mortality for the whole category of lymphomas among different countries. On the other hand data concerning different subclassifications of lymphomas in different countries are not available. The incidence of NHL increased in recent years in USA and in the European countries. Data from the Cancer Registry in the province of Varese, the registry with the longest high-quality registration period in Italy, indicate the same tendency. Also mortality rates show an increasing trend in Europe and in the USA. The cause of changing in incidence and in mortality rates for NHL are unknown. Anyhow many factors, viral, chemical and immunological are known to be associated to the occurrence of lymphomas. Risk factors and in particular environmental factors are reviewed. Problematic aspects, in relation to methodologies adopted in these studies, are focused.