XII 



Cancer 



H 



The growth of an animal organism is, as we have seen, very accurately 

 controlled. Every kind of cell keeps in place and in step with the 

 others. We might wonder what would happen if the controlling 

 mechanism, whatever it is, were to break down so that some cells 

 just went on multiplying without stopping. This is precisely what 

 happens with malignant cells, which form cancers. Not only do they 

 escape from the control of the organism, but they often infiltrate 

 through tissues other than the one in which they originated. They 

 may also find their way with the blood stream or the lymph into 

 many other tissues and they finally cause death, either by interfering 

 with the working of the body or by taking all the available nourish- 

 ment and so starving the rest of the body. 



At the present time one person in six in Britain and one in seven 

 in the United States die of cancer. An enormous amount of work has 

 been done to try to discover why cancerous cells escape the normal 

 body controls; and also to find ways of killing them without destroy- 

 ing too many healthy cells at the same time. However, until we know 

 what mechanism controls cell multiplication in a healthy body, it 

 will be difficult and perhaps impossible to specify what has gone 

 wrong in a cancerous growth. 



Nevertheless, a great deal of information about the origin of cancer 

 (carcinogenesis) has been found, and it is probable that many of the 

 relevant facts are known, although it is not yet possible to fit them 

 all into a coherent pattern. 



Numerous theories of the origin of cancer have been put forward, 

 all of which can produce some facts and observations which they are 

 able to explain. These theories fall into three types : 



(1) The Mutation Theory: According to this, a cell in the body 

 undergoes a mutation as a result of which it becomes essentially a 

 different kind of cell. Of course many changes of this type will pro- 

 duce cells which cannot live or at least are unable to multiply. But 



