NEOPLASTIC DISEASE 



(i) In all advanced countries with adequate statistics there 

 has been a steep and continuing rise in leukaemia. 

 (As in all other statistical statements leukaemia covers 

 all types.) 



(ii) The incidence of leukaemia is higher 



(a) in advanced as against backward countries: Den- 

 mark > U.S.A. > Canada > Australia > England and 

 Wales > Eire. 



(b) in higher social classes : White > coloured in U.S.A. 

 In England and Wales Social Classes i and ii: 176, 125; 

 III, IV, v: 90, 93, 84 (in terms of average 100 for all 

 classes) . 



{c) in males rather than females, especially for chronic 

 lymphatic leukaemia. 

 (d) in urban as against rural populations, 

 (iii) Increasing incidence over the last 30 years has involved 

 all ages and, by implication, all three types of the disease. 

 (iv) The age incidence of leukaemia in childhood has 

 shown important changes in the emergence of a well- 

 marked peak of incidence between 3 and 4 years. This 

 peak has more than doubled the incidence o to 5 since 

 1920. It is not seen in the curve for coloured popula- 

 tions in the United States. The increase is far greater 

 than would be produced as a result of pelvic X-rays in 

 pregnancy and offers a very important problem for 

 aetiological diagnosis. 

 The age incidence of chronic lymphatic leukaemia is that 

 of a normal cancer but acute and myeloid leukaemias, which 

 are those for which radiation has been incriminated, differ 

 sharply. There is much to suggest that a single somatic 

 mutational event or its equivalent — rather than a sequence 

 of such events — is the rate-determining factor here. As a 

 corollary, the effect of specifically mutagenic agents might 

 well be more strikingly displayed in the production of 

 leukaemia than in carcinogenesis. This seems to hold for 

 ionizing radiation, in so far as this is an effective stimulus 



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