During embryonic life cell proliferation must take place at a truly remarkable rate. When we recollect that the child at birth, plus the placenta, &c., have all developed in the short space of nine months from a single fertilized ovum, we must realize that the rate of cell proliferation is one with which few malignant growths could complete. Wherein lies the difference? The one is cell multiplication under guidance, and the other the same thing without any control.
Now, this “guidance” is a very wonderful thing. The fertilized ovum splits up into cells which soon become changed into various different kinds. There is continued growth and differentiation until all the various kinds of cells found in the body have been formed, after which cells, for the most part, produce their own kind only. The rate of growth of the various types of cell varies tremendously at different periods of the antenatal life. This guiding control, therefore, commands not only the type of growth, but also the rate of cell proliferation, increasing or decreasing it according to the needs of the organism.
What is this controlling influence? I doubt very much if mortal man will ever know. It is of the very essence of our spiritual existence. This cell control continues, also, throughout the entire life of the individual. We see it, for instance, in the repair of surface abrasion. The epithelial cells proliferate until the abrasion is healed and then proliferation stops. The control is still functioning. We see, then, that this power of reproduction is present in every cell during the period of growth, and in many cells, e.g., epithelial and endothelial, during the entire life of the individual.
Now I wish to suggest to you that the transition from the normal cell to the malignant is not due to any increased power which the cell has acquired, but is due to the breaking, for some reason, of that control under which all cells live and function, giving vent to that potential malignancy which is present in every cell. The earlier in the life of the individual the control is broken, the more potent is the latent power in the cell, hence the younger the victim of this disease, the more malignant, as a rule, is the growth.
Although it is highly improbable that we shall ever know the inner workings of the cell control, there is no reason, why, through time, we should not be able to tell with considerable accuracy the factors which lead to the severance of the bond between the cell and the higher influence. One factor is now fairly generally recognized, viz., the factor of local irritation. Evidence of this is found in chimney sweep’s cancer, cancer of the lip in clay-pipe smokers (probably due to heat), cancer of the tongue starting at the site of tooth irritation, cancer arising from continued exposure to X-rays. The common sites of cancer in the gastro-intestinal tract are just those parts where we would expect irritation to be most in evidence. Many other clinical examples might be given. In addition, we have the artificial production in animals of tumours very similar to cancer by local irritation. Taken altogether, the evidence that continued local irritation plays an important part in the breaking of the cell-controlling power is almost irresistible.
The ordinary effect of temporary local irritation is to stimulate the tissues to repair the damage done by the irritant. The higher control is slackened, the cells proliferate, and the repair is made good. If the irritation is continued the cell proliferation is continuous, the control is slackened to its utmost capacity and ultimately snaps. I use that expression as the nearest simile I can think of is that of an elastic band which will stretch so far and no further. Local irritation may be due, of course, to a great variety of causes. In addition to the examples already given, I would mention irritation surrounding long-standing simple ulceration; excessive stimulation following continued abuse of condiments, alcohol or drugs; chronic catarrh, e.g., of the cervix, uteri.