LEUKAEMOGENESIS: QUANTITATIVE ASPECTS 



AND CO-FACTOKS 



R. H. MOLE 

 M.R.C. Radiobiological Research Unit, Harwell, England 



INTRODUCTION 



Leukaemogenesis has been singled out from carcinogenesis and given twice 

 the time in the programme for the reasons, I suppose, that even small doses 

 of radiation, as received in diagnostic radiology, appear to be leukaemogenic 

 in man, that enough radiation-induced human leukaemia has occurred to 

 suggest quantitiative dose-response relationships, and that the vast amount 

 of experimental work which has been done might have been expected by now 

 to have turned up something definite and important about mechanisms. 



THE PHENOMENOLOGICAL DEFINITION OF LEUKAEMIA 



Leukaemia, like many other indispensable terms in current use in medicine, 

 and indeed in biology generally, is merely a descriptive word for a group of 

 phenomena whose nature is not properly understood but which can readily be 

 recognized by a trained observer. The gross symptoms of leukaemia may be 

 highly variable and the underlying common feature is a progressive and 

 ultimately lethal proliferation of cells which are morphologically not too 

 unlike one or other (or more than one) of the different kinds of cells which 

 make up the normal haematopoietic, lymphopoietic and reticular tissues of the 

 body. Individual cases of leukaemia are usually named according to the 

 predominant cell-type and it is a basic assumption that the particular cell (or 

 cells) from which the leukaemia started is (or are) related to the predominant 

 cell in the same way as stem-cells are related to their differentiated progeny, 

 although in leukaemia, both generally and in specific cases, it is always uncer- 

 tain just how far back in the ceU lineage one has to go to find the cell (or cells) 

 in which'the leukaemia^originated. TheVarieties'of leukaemia are given specific 

 names but, as in taxonomy in general, the boundaries between named species 

 and even the grouping of particular sets of species into genera or families is 

 often somewhat arbitrary.f If this is forgotten it becomes all too easy to talk 



t The demonstration of hybridization between somatic cells in tissue culture (Sorieul and 

 Ephrussi, 1961) may make it possible to apply to the problems of classification of leukaemia a 

 similar criterion to that used in the classification of species, the possibility or otherwise of 

 interbreeding. 



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