4 K. H. MOLE 



about leukaemia as if it were one "thing" and thus to asume that there must 

 necessarily be a common basic mechanism for every case of leukaemia. In this 

 and many other ways the problems of leukaemia are just the same as the 

 problems of cancer and it is generally, though not quite universally, accepted 

 that leukaemia is in fact cancer of the haematopoietic tissues. 



It is indeed possible to imagine that all leukaemias originate in toti- 

 potent cells which normally are capable of giving rise to fuUy differentiated 

 daughter-ceUs as different as smaU lymphocytes, granulocytic leucocytes, 

 erythrocytes and macrophages. The predominant cell in different cases of 

 leukaemia would then depend on the particular route of biological develop- 

 ment of the daughter-cells of the "leukaemic" stem-cell and how far along 

 that route their mock-differentiation has proceeded. There might then be a 

 single basis for aU leukaemias, the particular morphological features of the 

 predominant cells of a particular case being an "accidental" consequence of 

 some factor determining cell differentiation. On the other hand, most workers 

 nowadays would believe that there are several reaUy different kinds of 

 leukaemia. The epidemiological evidence certainly suggests that the causes 

 of acute leukaemia, of chronic myeloid leukaemia and of chronic lymphatic 

 leukaemia in man are distinct (Court Brown and DoU, 1959) and it is important 

 to note that radiation has been shown to increase the first two kinds of 

 leukaemia but not the third. 



BIOLOGICAL CHARACTERS OF DEVELOPED LEUKAEMIA 



Grafting leukaemic cells into genetically acceptable donors is followed by 

 their multiplication. The cell in developed leukaemia has permanent and 

 inheritable properties and it must be genetically different from normal cells. 



Much more interesting is the progressive transformation of these properties 

 as the leukaemic ceUs continue to multiply. This occurs not only on trans- 

 plantation but also in the primary host of origin where leukaemic cells are not 

 by any means always identical (cf. Hauschka, 1961). In this respect leukaemic 

 cells are qualitatively different from normal cells for not only do biochemical 

 and metabolic properties change but the chromosomal constitution can also 

 change. There is a characteristic plasticity of chromosomal number and 

 morphology which just does not, and indeed could not, occur in normal ceUs 

 if ordinary ideas of genetic determination are true. 



Individual cases of leukaemia often have a quality of uniqueness. The 

 experimenter with inbred strains of mice can easily forget this but a competent 

 clinical haematologist in a hospital with, say, a dozen cases of leukaemia can 

 usually tell by loolcing at the cells in a blood smear from which case it came. 

 No cytologist, however competent, can do this with a set of blood smears 

 from normal people. 



