Exceedingly vague notions have prevailed concerning the nature and origin of tumors, and, while the clinical observations of writers in the past will never lose their value, the ideas which have prevailed concerning their pathology constitute interesting reading in a historical sense, but are now of small value. Accurate notions scarcely prevailed until Virchow demonstrated that tumor cells nowise differ from cell types which are met either in embryonic or in adult tissues. Tumors, like all other parts of the body, are built up of cells, and the points concerning which we need most light regard the influences which determine cell overproduction in these characteristic forms. Concerning the views that have prevailed, this is scarcely the place in which to offer an epitome. I shall therefore take up but few of the explanations which have been offered to account for tumor growth, and will emphasize that, according to our present light, there is no explanation sufficient to cover all cases, but that it is now one cause and now another which may determine this peculiar form of cell activity.
Irritation and Trauma.
—The effort is often made to explain the presence of tumors upon the hypothesis or the known fact of some previous injury. Frequently tumors appear in sites where there have been previous traumatisms, but this sequence of events by no means proves a definite relation of cause and effect. On the other hand, there are forms of irritation which are often followed by tumor formations. Probably no woman escapes without one or more bumps or bruises upon the breast, yet they do not produce tumors in more than a trifling proportion of cases. Per contra, upon the lower lip of inveterate clay-pipe smokers and the scrotum of chimney-sweepers there develop certain forms of malignant ulcer (epithelioma) which so often and so significantly follow upon the irritation thus produced that it is impossible to avoid conviction that one is the cause of the other. Should events prove the parasitic nature of any of these growths they will also prove that the irritation causes surface lesions through which infection easily occurs. In regard to the relative frequency with which cancer in some form follows trauma we should not forget the well-known fact that traumatism usually diminishes tissue resistance. If cancer be an expression of infection, as many (including the writer) believe, the possible relation between trauma and malignant disease may be better appreciated.
Inflammation.
—This refers to inflammation in the sense in which it has been used in the past, implying a variable condition, sometimes including and sometimes excluding infection, the term covering a confused mixture of irritation, hyperemia, and infection. In so far as it concerns inflammation as considered in the present work it should not be here included, since inflammation (i. e., infection) produces neoplasms of a class considered in Part II and is distinctly ruled out from present consideration (i. e., the infectious granulomas).
If inflammation in the former sense be more than hyperemia it may be regarded as predisposing to cell activity, but not necessarily to tumor formation as distinguished from hypertrophy of a given part or tissue. If it refer to irritation, this has been acknowledged as a factor in the etiology of tumors, but as an uncertain one. Cancer of the gall-bladder or liver, which occasionally results from the irritation of a gallstone, or the cancer of the breast that follows eczema of the nipple, may be regarded in this light as additional illustrations if it is preferred to interpret them in this way. If by inflammation be meant the infectious granulomas, they have already been considered. As the term “inflammation” can scarcely mean anything except hyperemia, irritation, or infection, we seem to have completely ruled it out from consideration as by itself an active cause leading to tumor formation.
The Embryonal Hypothesis of Cohnheim.
—This in its ingenuity and in its applicability is a fascinating explanation, which is undoubtedly sufficient for at least a certain number of instances. According to Cohnheim, only one causal factor for tumors exists—i. e., anomalous embryonic arrangement. He regards them as entirely of embryonal origin, no matter how late in life they may develop and appear. Briefly summarizing his views, they are to the effect that in the early stages of embryonal development there are produced more cells than are necessary for the construction of a certain part, so that a number of them remain superfluous. While these may remain very small, they possess, on account of their embryonal nature, a potent proliferating power. This superfluous cell material may be distributed uniformly, in which case it will develop whole system arrangements, like supernumerary fingers, etc., or it may remain by itself in one place, and will then develop a tumor. In the latter case the tumor may appear early or not until late in life, according to the time at which the cell collection receives the necessary stimulus, or because of its suppression by resistance of surrounding structures. It may be an irritation or an injury, such as above alluded to, which shall give it this stimulus; as, for example, it is reasonable to think that certain nevi and other congenital conditions which develop later into cancers do so in accordance with this view. Surgeons generally find little fault with Cohnheim’s hypothesis, except that as yet they decline to see in it an explanation for all cases. Nevertheless for dermoid and teratomatous, and for all heteroblastic tumors, it seems to afford the only tenable explanation. Thus chondromas of the parotid and of the testicle are most easily explained in this way, and that cartilaginous islands occur in the shafts of adult bones is well known.
Heredity.
—In regard to heredity being a factor in the etiology of neoplasms there is reason to believe that a favorable tissue disposition may be inherited, but there is nothing to show that it permits the actual transmission of the disease.