Cancer 95 



cell and of reacting with it. Some of these substances react very 

 readily with the nucleic acid (dna) of the chromosomes; and when 

 such reactions occur, the normal mechanism of cell division may be 

 upset, and also the message carried by the genie code may also be 

 interfered with. 



Because such reactions occur, some carcinogenic chemicals are 

 used extensively as anticancer agents. They interfere with cell division 

 and may diminish the rate of growth altogether. The destruction of 

 cancer cells by drugs is, however, a very difficult problem. A success- 

 ful anticancer agent is one which attacks cancer cells, while leaving 

 normal cells relatively unharmed. One of the few distinctive charac- 

 teristics of cancer cells is that they are multiplying rapidly, so that 

 it would appear that the most likely approach would be to destroy 

 cells while they are in the process of cell division. The most likely 

 anticancer agents are those which interfere with cell division and 

 these are also usually mutagens. 



It was pointed out by Haddow that most carcinogens are also 

 anticancer agents. This might seem to be a paradox, but it must be 

 remembered that the initiation of a cancerous growth is a very rare 

 event. These substances more frequently cause other kinds of damage 

 to the living cells, so that their use as anticancer agents is quite 

 feasible. 



Ionising radiations such as X-rays and radiations from radioactive 

 substances also conform with this rule. It was in fact discovered 

 very soon after Roentgen's discovery of X-rays that they not only 

 cause serious 'burns', which frequently become malignant; but they 

 can also, when carefully employed, be used to destroy malignant 

 growths. In many ways these radiations are an ideal method of deal- 

 ing with malignant growths near the surface of the body. The cancer 

 cells are more sensitive to the radiations than normal healthy cells 

 usually are, so that it is possible to destroy them without injuring 

 healthy tissue too much; and it is possible to localize the exposure to 

 a considerable extent. However, X-rays are not invariably successful 

 as a small proportion of the cancer cells may escape, especially when 

 secondary growths have started, and these may be a centre for new 

 malignant growths. For this reason, if it could be achieved, treatment 

 by drugs which would specifically destroy malignant cells is much 

 to be desired, but only limited successes have been achieved so far. 

 The most successful agents used so far, apart from radiations, are : 



(i) compounds of the 'mustard' series, which, as already mentioned, 

 are mutagens and are capable of reacting with the chromosomes. 



(ii) antipurines; these are substances which are very similar to the 



