STRONTIUM-90 AND CARCINOGENESIS IN RATS 143 



controls in the A group, 3-75% in the treated B group and 6-25% in the treated C group. 

 The body burdens of ^^Sr in A, B, C and D groups were 1 /xc, 2 jxc, 11 /xc and 33 ^c 



respectively. 



UPTON: What sort of leukaemia was this? 



casaeett: Lymphatic. 



mole: So this is really three cases of leukaemia in group B and five cases of leukaemia in 



group C. Three out of eighty or five out of eighty are different. Three out of eighty and 



nothing out of eighty are not different. Do you think that groups B and C are really 



different? 



CASARETT: I do not insist on that myself. I do feel convinced that leukaemia was produced 

 by the treatment but the difference between B and C to me is questionable. 

 pocHm: Would you consider A, B, C and D are different when you have x^ of 8-5? ^ 

 CASARETT: As I indicated, my conviction that this treatment has produced leukaemia is 

 based not solely on the number of animals in this experiment but on knowledge that in a 

 careful study, haematologically and pathologically, of all animals that died in our 

 colony, we found leukaemia very rarely, extremely rarely. 



pochin: I was not questioning the evidence but merely whether it is different between 

 the four-dose levels. 



CASARETT: This I do not yet know. These are four experiments of a large group in which 

 different age, different feeding doses and different body burdens are being investigated. 

 lamerton: I take issue with Dr. Mole when he says that there is no difference between 

 zero out of eighty and three out of eighty; there is in fact quite a difference. I think we 

 have to recognize particularly in carcinogenesis when one does not use large numbers of 

 animals that one has sometimes to accept results which are statistically significant at the 

 5% level. We are far too inclined to say that a thing is not different because it is not a 

 20 to I chance. May I make a second pomt about something Dr. Gopal-Ayengar said. He 

 was comparing bone tumour and leukaemias incidence. In point of fact there is probably 

 quite a difference in the radiation dose received by some of the osteogenic cells and by 

 the bone-marrow cells. Even Avith ^°St in the mouse there may be a difference of 3 to 1 or 

 5 to 1 if, for example one considers the osteogenic cells at the face of the plate, you are 

 in fact giving osteogenic cells quite a large dose in some cases. And secondly, you said that 

 the osteoblast was much more radioresistant than the blood-forming cells. What do you 

 really mean by this? 



gopal-ayengar: I mean that the ostegoenic cells are relatively less sensitive than the 

 blood-forming cells. 



UPTON: This experiment has raised several interesting points. First of all, squamous cell 

 carcinoma. I would Uke to enquire whether there was ulceration of the skin or any 

 noticeable epithelial breakdown ui the skin. Then the other point is that in a variety of 

 experiments, with internal emitters, not necessarily with ^2? but ^^Sr or ^^Sr leukaemias 

 have appeared in increased numbers in rats and in mice, despite the observation that 

 whole-body radiation is much more effective, if not actually necessary, to produce this 

 kind of leukaemia. In view of the dose-rate dependency, admittedly complex as Dr. 

 Mole said yesterday, I think this is a very interesting experimental finding. In the work 

 we did with RF mice we thought that we were much more Ukely to induce myeloid 

 leukaemias with internally administered ^^Sr or ^"Sr. To our great surprise, we did not 

 affect the myeloid leukaemia incidence at all with the doses used, but we did increase the 

 incidence of thymic lymphoid leukemias. 



mole: I would like to pursue something Dr. Upton said. Although the animals were 

 grouped according to the terminal body burden, they were in fact given a great deal 

 more strontium in their drinking water, 10 or 100 times more, and presumably a good 



