Future of Infectious and Malignant Diseases 
either replace the normal cell constituents with others or add a 
new constituent to the pre-existing ones. Within this classifi- 
cation, the acquisition of tumour cell characteristics from with- 
out could be induced by the so-called tumour viruses, or their 
essential constituents, or by any other natural or artificial 
macromolecules which are able to invade a cell and function 
as described above. 
Autonomy and dependence 
Tumour cells which acquire their character from within or 
from without may either become autonomous or remain 
dependent. 
(a) The autonomous cancer cells produce daughter cells 
regardless of repetition of the original inducing event. These 
daughter cells will then divide again and create a generation of 
cells which is essentially immortal. Most, if not all, of the 
tumours which acquire their character from within belong to 
this category. Tumour viruses which contain deoxyribonucleic 
acid (DNA) also seem to induce autonomous tumours. 
(b) The dependent tumour cells rely on multiplication of the 
inducing agent in order to survive as cancer cells. Thus they 
may die out if they are not re-invaded by the original agent. 
Most, if not all, tumours caused by viruses containing ribo- 
nucleic acid (RNA) belong to this category and, as shown in 
Fig. 2c, the invader has to move from cell to cell since its 
sojourn is terminated by the destruction of its abode. 
For the sake of simplicity, this description of the genesis of a 
malignant tumour has been restricted to these single events 
which actually trigger the transformation of a normal cell into a 
tumour cell. It is recognized, of course, that this is at most a 
verisimilitude of the natural event, and that many other factors 
have been disregarded which play a paramount réle in carcino- 
genesis today or may do so tomorrow. 
Prophylactic approaches 
Prophylactic measures will be based upon protection against 
the precipitating event, when and if it is known. It is not my 
207 
