One disease which is considered as the leading dreaded disease in the world that has claimed many lives is known as the big “C” or cancer. What do we mean by the words “cancer,” “malig¬nant tumor,” or just a “growth”? It has been described simply and clearly in the following words: “In the very beginning one or two or more cells, always a few but we do not know how many, become possessed of an urge to multiplication beyond anything that can be controlled by the growth-regulating forces of the body. These cells are the first tumor cells. They begin to multiply. After a time, we know not how soon but certain¬ly quite early, no more normal cells become cancerous, the whole of the cancerous elements of the growing tumor being thence forward formed solely of cells which are direct lineal descendants of cells which became cancerous at the beginning.”
These sentences describe adequately what a tumor is. The next question then is what is it that causes the cells to start this uncontrolled multiplication and to break away from their allegiance to the organism as a whole, so that part of the body becomes, as it were, a traitor to the rest? The answer to this question, upon which the fate of thousands turns, is being sought in many laboratories all over the world. That it will be found one day is certain and may that day come soon. Cancer and war, those twin scourges of mankind, are analogous in one respect in that both are a form of betrayal, in one case by part of the individual organism, in the other by part of the community. Man shares with the rat the distinction of preying upon his own kind.
What has tumors got to do with the viruses? What is the connection between the viruses and tumors? This cannot yet be an¬swered in its entirety. However it is quite safe to say that some tumors are associated with viruses. It is noteworthy to mention that a long time ago, just before the First World War, an American pathologist named Rous discovered a fowl with a malignant tumor. This tumor is now called as the Rous sarcoma. Experiments with this tumor showed that it could be transmitted from fowl to fowl by injection. They also demonstrated something else. If the tumor was taken from the fowl, ground up and the extract filtered through a bacteria-proof filter, then the filtrate which contained no bacteria was capable, when injected into another fowl, of giving rise to a similar tumor. The Rous sarcoma thus behaves precisely like many other undoubted virus diseases and is quite rightly included in that category. The virus which causes Rous sarcoma can be viewed under a high power microscope like the electron microscope.
Rabbits suffer from a disease in which small wart-like outgrowths, commonly known as papilloma, appear on the skin of the ears. A small percentage of papillomas become malignant and develop into true cancers. This disease is also caused by a virus that can only be seen using high power microscopes. This can be transmitted from rabbit to rabbit by inoculation with bacteria-free filtrates. Another example of a transmissible tumor has recently been discovered in a certain species of frog.
As a rule, experimental cancers are only transmissible by grafts. Graft is done by implanting the growth bodily in the new host so that it continues to grow as a whole. In the case of the Rous sarcoma and the rabbit papilloma, however, true filterable viruses are concerned.
Most experimental cancers, induced by tar and so forth, are not transmissible by filtered extracts but only by grafting. Nevertheless there is some evidence that a virus may be present in these also, even though its presence can be detected only by indirect means. Although these parti¬cular tumors are not transmissible by inoculation, certain serological reactions suggest that a virus may be there. We have studied that some of tumors are due to viruses. Some examples were previously mentioned. What about the relationship of viruses to cancer as a whole? It must be admitted that there is a good deal of evidence against the virus theory. First of all, though we have seen examples of tumors which are demonstrably due to a filterable virus the great majority of tumors are not filterable. Then again, cancer is not contagious. It is clear that cancer cannot be “caught” in the way that many infectious virus diseases are transmitted. There are certain chemical and physical agents which are called “carcinogens”. Carcinogens mean cancer-causing or in other words they can determine the appearance of cancer. Certain mineral oils and tarry substances for example, produce cancer under particular industrial or occupational conditions; “mule-spinner’s” and “sweeps’ cancer” are cases in point. There are many of these carcinogens just like various chemicals and hormones, and equally important is the tar.
How can we reconcile the theory that viruses may be the cause of cancer with the known behavior of these carcinogenic substances which apparently give rise to cancers on their own? The simplest explanation is to suppose that there is already a virus present which lies hidden or latent in the cells of the organism. Some factor, such as the tar in one case and possibly some other unknown factor in other cases, then stimulates the virus into action, and this causes the cells to begin their headlong and uncontrolled multiplication.