Occupation has been questioned, but with most unsatisfactory results, for in some statistics which have been gathered cancer has been observed in those following all possible pursuits: and while laborers stood first on the list, clergymen stood fourth, while carters, threshers, and guides, who would be exposed to local injury, were at the bottom of a long list. It has been found, however, to be more frequent in trades or occupations in which the individual is most subject to the habitual abuse of alcoholics, as in bartenders, printers, etc.
We see, then, that thus far no satisfactory cause has been established for the occurrence of cancer, much less for the steady and great increase of the disease of late years. And as far as can be learned, no measures are recognized, or at least generally adopted, to prevent its occurrence or recurrence; although, as already stated, modern surgery has seemed to improve the statistics in regard to its mortality in certain forms or locations, and the X-ray and radium have certainly also been able to remove, perhaps temporarily, some of the products of the disease.
We come then to the question, what is the real nature of cancer? Alas, all scientific, experimental, and clinical investigations have failed to solve the problem, except that all “evidence points to the conclusion that cancer is to be considered as a pathological disturbance of the normal cell life,” from some unknown cause. A curious suggestion has been made by Schmidt, who found that of 241 cases of cancer of the chylopoietic system, 180 had never had any infectious disease of childhood, and 99 went through life without any infection of any kind; the figures point to the existence of a cancer diathesis—one which is resistent to germs.
It would carry us too far from the practical side of our subject, even if we were at all able, to present or analyze the vast number of contributions which have been made to the pathological histology of cancer, and the changes which take place in the transformation of normal cells into those of malignant character: the amount of microscopic work which has been done along this line can hardly be imagined, and the literature relating to it is enormous.
Ewing, accepting the definition that the cancer process is “atypical and destructive proliferation of epithelium,” quotes Ribert as saying that “no one has ever seen the beginnings of mammary cancer”: but he does not bring us much nearer to the solution of the cancer problem than we were before. Bainbridge rejects all possibility of a blood condition, and finds the only solution of it in the early removal of everything which is thought to lead to cancer, even the simplest benign new formations, but Ewing states that “in some cases carcinoma has developed after excision of wholly benign fibro-adenoma”: and the immense number of cases of recurrent cancer after operations shows that we must look further than surgery if we wish to stay the progress of this formidable disease.
It would be useless to attempt to present the many theories which have been advanced relating to cellular metaplasia, or even to detail all the more or less accepted views in regard to the manner in which normal cells change and degenerate into those of malignant character: but some of the principal facts may be of service in understanding somewhat of the mode of development of malignant tissue from that which has been normal.
The statement of Virchow, “Omnis cellula e cellula,” that is, “where a cell arises there a cell must have previously existed, just as an animal can spring only from an animal and a plant from a plant,” forms the basis of all study on the genesis of cancer and all tumor formation; karyokinesis, or indirect nuclear or cell division, is at the bottom of all growth, both normal and malignant, and the two classes of growth differ only in their methods and activity. In healthy tissues cell proliferation and destruction proceed in an orderly manner, forming homologous structures, as when the hair and nails are constantly produced from newly formed cells at the root, and the result of this new growth is removed mechanically when the hair and nails are cut from time to time, or the hairs fall out. In the case of the skin the epidermal layers are pushed forward and finally exfoliated as useless epithelial débris.
With the cells composing other, or internal structures, however, the process is different. For here each normal cell reproduces others of homologous structure, and the different parts of the system are thus kept in active service through anabolism, by means of which new cells are formed with renewed vitality, and the older, or effete cells are removed by catabolism; the elements of which they are composed are thus split up into their component parts, and carried off by the blood or lymph stream, and are then either discharged as effete substances or reutilized in the system, along physiological lines. Wakefield has pretty clearly shown that the developing cancer cell is the product of sub-catabolism, or a sub-oxygenation, induced by hyperacidity or oxidase deficiency in the surrounding medium of the blood plasma.
A great deal of thought, study, and speculation have been given in regard to the behavior of the cells themselves, and strong arguments are adduced for a local cell pathology, that is, regarding the cells as “autonomous beings, possessed of morphological and physiological independence.” But on the other hand we must recognize some restraining influence which continually causes the great mass of cells to reproduce those of homologous structure, in an orderly manner, and only very rarely some of them to break loose and form tumors, which may then become malignant and even destroy life. How this restraining influence is modified or withdrawn is, of course, a part of the problem of cancer. Those who maintain their autogenous character lay great stress upon the polarity of cells, and the relation of the centrosome to the nucleus, indicating a change in the polar axis in cells about to be cancer-genetic, as does Ewing in his recent classical study of pre-cancerous lesions. But whatever changes are observed microscopically we must recognize that the cells themselves must be influenced ultimately by that mysterious force which we call life, which ends with its extinction from the body as a whole, and which is ultimately related to nerve action. We must also recognize that the cells everywhere depend for their life and activity upon the plasma in which they are bathed and from whence they draw their sustenance; and this plasma is renewed day by day from the food and drink taken.
Students of cancer are more and more recognizing and acknowledging that “all these phenomena, apparently so different, are merely protean manifestations of one common process which underlies and is the cause of them all, to wit, cell growth and proliferation. The particular outcome of the process in any given case is due to the influence of the conditions of nutrition—understanding by this term the whole of the material changes wrought in the organism through its relation with the surrounding world. This being so it is easy to understand how, under favorable conditions, certain cells may take on independent action, growing and multiplying without regard to the requirements of adjacent tissues and of the organism as a whole.”