Heredity has been advanced as a cause, but statistics fail to verify this in any degree whatever. While certain instances have been brought forward in which heredity seemed evident, the study of large numbers of those afflicted with cancer, in connection with others free from the disease, has shown almost the same proportion of antecedents with cancer in both classes of persons; although some recent evidence seems to show that there is some tendency in different families for different organs. Experimental studies have, it is true, seemed to demonstrate that tumors occur apparently along hereditary lines in some animals in regard to certain organs; but in these instances it is to be remembered that the animals were kept in captivity, and all fed alike, conditions which have been found to cause the development of malignant disease in wild animals when confined in Zoölogical Gardens.
In former years malaria was believed to have an influence in the production of cancer, and some investigators have thought to trace the prevalence of the disease to telluric influences, showing a preponderance of cases along certain water courses, or in certain streets or houses; but no definite proof of such connection has ever been established, and this theory is dismissed by the best authorities. Syphilis, in its latent effects, has also been claimed as an element in the causation of cancer, and undoubtedly the disease may develop, in suitable persons, upon old syphilitic lesions, especially about the mouth, anus, and genital region: but no one well informed in regard to cancer would regard syphilis as the real cause of the disease. All these and other etiological propositions are no longer considered to be tenable, and the very multiplicity of suggested causes shows that we are yet very far from the true etiology of cancer.
Age undoubtedly has a powerful influence in the development of cancer, the vast majority of cases occurring after the age of forty or fifty. But, again, this does not at all explain the true nature of the disease, for only a certain proportion of elderly people are so afflicted, and malignant tumors have been observed in those of all ages, and even in young children. The degeneration of tissue belonging to advancing years undoubtedly renders it more susceptible to malignant disease, but this does not explain why one person is affected and not another, nor why the tissues in one locality or another take on this morbid action.
More recent scientific study has attempted to show that cancer originates from what are called “embryonic rests,” or pre-natal, wrongly placed, tissue elements, which at some time or other take on morbid action and develop into what we know as the various forms of cancer. Williams says, “From a biological standpoint tumor formation must be regarded as a phenomenon of the same order as reproduction in general: that is to say, as a special form of overgrowth of the individual.” But here again it is necessary to determine what causes them at certain times and in certain places to thus proliferate and form new tissue, which then becomes malignant and may proceed to destroy all contiguous tissues, and even to cause death.
Traumatism has been claimed by many as the cause which determines the activity of the misplaced cells, and starts them on their disastrous or rampant course: the various percentages of the cases in which it was believed that traumatism started up the malignant process has varied greatly with different observers, even up to 50 per cent, or more. But it is far from proven that this is always the case, nor does local injury in any way explain the persistency with which malignant disease, when once started, pursues its destructive and even fatal career; nor can traumatism account for the great tendency to recurrence constantly observed, either in the former site or at some distant focus, through the agency of the lymphatic or vascular system. For of multitudinous traumatisms, even in cancer subjects, how few ever develop into malignant disease!
It would seem, therefore, that for the development of the local manifestation of cancer (the tumor or new growth) three elements are requisite, namely: 1. A predisposition or suitable blood condition. 2. A local stimulation or irritation of the part affected, upon, 3. The site of an “embryonic rest.”
On the basis of the embryonic theory surgeons have of late most earnestly advocated the very early and complete removal of malignant lesions, including those of suspected malignancy, and even also the removal of many innocent lesions which are observed occasionally to lead to cancerous formation; and unless a better plan can be determined this cannot be urged too strongly in proper cases.
But while early operation has improved surgical statistics, it has not contributed to our real knowledge of the basic cause of cancer, nor has it taught us why those lesions or “embryonic rests” will remain quiescent for years, or prove harmless in some individuals, while in others they become most formidable agents of destruction. For it is now recognized that these wrongly placed tissue elements are very common anatomical or histological accidents, indeed it is claimed that they occur and exist in every individual: and the removal of isolated “embryonic rests” which have developed into cancer, does not by any means prevent the transformation of other similarly misplaced cells into malignant disease, as the frequent recurrence of cancer after operation demonstrates.
The same is true of the many and various forms of treatment other than surgical excision, such as deep acting caustics, and even the X-ray and radium, which like surgery, only remove the focus of possible systemic infection, and do not affect the basic cause of the complaint: this latter is being shown more and more, by scientific investigation and observation, to be associated with metabolic or chemico-physiological changes in the system, and evidence is accumulating that it is dependent upon them.
All this leads thoughtful persons to inquire if there is not some deeper, fundamental cause lying back of the trouble, which should be reached and rectified by medical skill and acumen, something to do with the life or diet of a person which renders the tissues liable to take on malignant disease. So that a recent surgical writer on cancer states that “all study, whether clinical, pathological, or experimental, points to the fact that there is some underlying, hidden cause which leads to that aberration in the action of tissue cells which we call cancer,” ... a cause “residing in only the cells themselves or in some abnormal chemical constitution of the plasma bathing the cells, or in both of these possibilities acting together.”