HILARY KOPROWSKI 
sense, since surgery will probably serve only to disseminate the 
causative agent through other cells and tissues of the body. 
However, irradiation may find a place in the treatment of this 
type of cancer since it has been shown that there are periods of 
relatively high sensitivity to irradiation during the multiplica- 
tion of ribonucleic acid viruses. 
Any possible therapeutic approach based on chemical means 
is even more conditioned by the type of the inducing event and 
by the characteristics of the tumour. A highly theoretical 
possibility of therapy of autonomous tumours which acquired 
their characteristics from within lies in the neutralization of the 
effect of the original inducing event. This may take place by 
administration of an as yet undiscovered chemical mutagen for 
mammalian cells. Another possibility involves the use of 
inhibitors of the metabolic function of a cell. The difficulty 
here lies not in the lack of available compounds which have 
been successfully incorporated into the metabolism of mam- 
malian cells, but in the ability of those compounds to reach the 
tumour zn situ in unaltered form and, what is more important, 
to distinguish specifically and sharply between the tumour cell — 
and the normal cell. 
The use of anti-metabolites in autonomous cancer acquired 
from without may offer a more hopeful approach, particularly 
if the original event introduced a macromolecule consisting of 
building blocks not found in normal cells. Inhibition of meta- 
bolic functions may also lead to the destruction of dependent 
tumours acquired from without. The latter task will be 
facilitated if the attempt is directed towards the reproducing 
agent without concomitant damage to the uninfected cells of 
the host. 
Future attempts at therapy of autonomous tumours acquired 
from within or from without based on biological approaches 
may include the use of “homing” devices such as cell-lysing 
viruses which display greater affinity for malignant cells than 
for normal cells. Reconstitution of normal cell functions based 
on the introduction into the malignant cell of normal cell 
constituents may also be feasible theoretically, if malignancy 
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