Leukaemia and smoking habits among United States veterans.

The relation between leukaemia and smoking habits was examined in data from the veterans' smoking study, a prospective study of mortality among 248,000 United States veterans, of whom 723 died of leukaemia during 1954-69. A significant increase in mortality from leukaemia among cigarette smokers (relative risk 1.53) was found, together with a dose-response relation with amount smoked (trend p less than 0.001). The relation was strongest (relative risk 1.72) for monocytic and chronic and unspecified myeloid leukaemias (ICD (7th revision) codes 204.1 and 204.2). For these leukaemias the increase was almost twofold (relative risk 1.93) among current smokers of over 20 cigarettes daily. Ex-cigarette smokers also showed an increase of leukaemia (relative risk 1.39; p less than 0.001). These findings are consistent with other studies and relevant to the interpretation of minor increases of leukaemia both in population and in individual based studies. If causal they also imply that smoking is responsible for many more deaths from leukaemia in adults than all other known causes combined.