Future of Infectious and Malignant Diseases 
depended on cessation of function of a genetic cellular consti- 
tuent (minus mutation). The missing constituent could then 
be introduced without a carrier or by a biological entity. This 
is a simple procedure in bacteria; it does occur in mammalian 
cells grown in tissue culture; it still remains in the realm of 
highly unreal possibilities for tumour tissue in situ. 
In dependent tumours acquired from without, ‘“homing”’ 
devices are not applicable but, in addition to other biological 
approaches mentioned above, therapy based on irreversible 
binding of the inducing agent by the creation of receptor sites 
other than those of the host’s cells may be considered. 
Prevention of exposure of man to environments which may 
be cancer-inducing and surgery seem to be the only hopeful 
approaches to the control of autonomous tumours acquired 
from within, and I regret to say that the negative evidence 
available up to now indicates that the majority of human 
tumours may belong to this category. Therapeutic attempts 
based on chemical and biological approaches may lead to 
simultaneous destruction of the tumour and its host. 
Although prevention of metastases and recurrences should be 
considered as the immediate goal of therapeutic approaches, 
ultimately the best, and perhaps the only, solution lies in 
development of recognition by the human host of the alien 
antigenic components of his tumour. Tumour antigens may 
become synthesized de novo as a specific protein of the malig- 
nant cells, or the antigen may reveal itself because of ‘‘inactiva- 
tion”’ of the normal antigenic cell constituents by the malignant 
process. If these specific antigens were to be associated with the 
surface of the cell, a recognition response on the part of the 
host might be expected. These recognition processes would be 
of the utmost importance in making any other therapeutic 
approach successful since the ultimate destruction of remnants 
or recurrences of the malignant cells would become subject, in 
contrast to all other therapies, to a destroying force, acting 
specifically from within. The possibilities of attacking malig- 
nancy by stimulation of defence mechanisms more primitive 
than those of immunological response will be discussed below. 
PA 
