STUDIES ON IMMUNITY IN CANCERS OF THE WHITE RAT : THE "PRECANCEROUS STATE" AND THE MECHANISM OF THE ORGAN RESISTANCE TO TUMOR GROWTH

Predisease: when does it make sense?

Screening often leads to finding conditions that are not at the stage or level that would classify them as disease but, at the same time, are not at a stage or level at which people can be declared entirely disease free. These "in-between" states have sometimes been designated as "predisease." Examples include precancerous lesions, increased intraocular pressure ("preglaucoma"), prediabetes, and prehypertension. When the goal of preventing adverse health outcomes is kept in mind, this review poses the idea that "predisease" as a category on which to act makes sense only if the following 3 conditions are met. First, the people designated as having predisease must be far more likely to develop disease than those not so designated. Second, there must be a feasible intervention that, when targeted to people with predisease, effectively reduces the likelihood of developing disease. Third, the benefits of intervening on predisease must outweigh the harms in the population. A systematic review of screening guidelines (published in 2003-2010) for 4 sample conditions (cervical cancer, glaucoma, diabetes, and hypertension) is included to assess whether they address these issues, followed by a discussion of the framework questions as they pertain to each condition.

ON THE CAUSE OF THE LOCALIZATION OF SECONDARY TUMORS AT POINTS OF INJURY

The cause of the frequent localization of secondary tumors at points of injury is not known. Our work deals with this problem. For the experiments the peritoneal cavity has been employed as offering relatively uncomplicated conditions, and the fate of mouse tumor brought into contact with a peritoneal lining injured in various ways has been studied. The injection of a suspension of mouse tumor into a healthy peritoneal cavity has little success as a rule compared with a similar injection into the subcutaneous tissue. We have found that the resistance of the peritoneal lining thus indicated can be largely if not completely abolished by the preliminary injection of a mechanical irritant (Kieselguhr, lycopodium). That the change thus brought about is independent of general immunity phenomena is shown by the fact that a local injury renders susceptible the part of the peritoneum immediately affected and that part only. Special tests show that the factor important in rendering the peritoneum more susceptible is the injury to the subendothelial connective tissue. Susceptibility persists after the endothelium has regenerated over the reacting connective tissue. Schmidt has found that the cells of tumor emboli in the pulmonary arterioles are able to penetrate the endothelium of the vessel only after they have been provided with a stroma from the subendothelial connective tissue. Our findings are easily explained on the basis thus suggested. A connective tissue highly cellular and perhaps still proliferating as the result of injury may well elaborate the stroma for a tumor more rapidly than normal connective tissue. Tests of growth in vitro support this idea. Connective tissue reacting to an injury grows profusely and almost immediately when incubated in plasma, whereas normal tissue from the same region shows usually no growth whatever. Dead tumor fragments in contact with the peritoneum cause a change favorable to the lodgment and growth of later tumor fragments. It seems not improbable that the peritoneal dissemination of certain human neoplasms may be accomplished indirectly through the death of the first tumor fragments cast off. Our observations have been purposely confined to the effects of injury on the peritoneal lining ; but they seem to afford the basis for a generalization. The secondary localization of tumors at points of injury may be attributed with good reason to the presence at such points of an active connective tissue capable of elaborating a stroma rapidly and abundantly. For it is the proliferation of the subendothelial connective tissue to form a supporting stroma that determines the fate of free tumor cells, whether these lie on the peritoneum or within a vessel.

CHANGES IN THE TISSUE SURROUNDING A GROWING TUMOR AND THE SIGNIFICANCE OF THE "PRECANCEROUS STATE."

An analysis of the results of the experiments reported in this investigation shows that the changes so frequently observed in tissues surrounding a growing tumor may be caused by different conditions. The development and growth of a malignant tumor depends upon a local interaction between tumor cells and organ cells. When the cells of a normal organ are capable of inhibiting tumor growth, then an impairment of the normal state of the parenchymatous cells of this particular organ is essential for the growth of the tumor. This "precancerous state" does not consist primarily of an inflammatory change in the adjacent connective tissue, as Ribbert and his followers maintain, but in a degeneration of the parenchymatous cells of the organ. If, in another instance, the cells of the normal organs are unable to inhibit the proliferation of the tumor cells, then no preparation of the cells of the organ for the tumor is necessary, i. e., no "precancerous state" is needed to enable the tumor to grow. On the other hand, the proliferating tumor cells injure normal cells, either mechanically or chemically, producing a condition that appears on superficial examination like that described as the "precancerous state." In reality, however, this condition is the resultant effect of the tumor growth and may be more correctly designated the "postcancerous state." In these conditions, then, von Hansemann's explanation of the phenomenon, and not Ribbert's, seems to be the correct one. Of still greater importance is the fact demonstrated in the last series of experiments; namely, that the general condition of resistance or immunity to cancer growth exerts a greater influence on the organism of the animal than any of the local conditions described above. The local resistance of a testicle to tumor growth in a generally susceptible animal may be overcome, but if an animal is made generally immune to the growth of cancer, neither the animal as a whole nor a single organ or tissue in it can be made susceptible to the growth of the tumor.

TUMOR INOCULATION INTO ORGANS AND THE ANALOGY BETWEEN HUMAN CANCER AND THE TUMORS OF WHITE MICE AND WHITE RATS

The analysis of the experiments described above indicates that tumors of the white rat or white mouse inoculated into parenchymatous organs acquire a different biological character from those inoculated subcutaneously. The latter are a great deal more benign in their behavior than human cancer or spontaneous tumors in the same species of animals. Tumors inoculated into organs, on the other hand, are quite identical in their biological behavior with the malignant tumors of animal and man. A conclusion must then be drawn, even a priori, that the method of inoculation into organs is a very important aid in the experimental investigation of cancer. It is true that the method is a great deal more complicated and time-consuming than the ordinary subcutaneous inoculation. The subcutaneous method is satisfactory for a number of cancer problems. One of these is the study of general susceptibility and resistance of the organism of the host to the inoculation of the tumors, and this is a subject of paramount importance in cancer research. On the other hand, the investigations of the writer (10) have shown that an animal may be susceptible to a subcutaneous inoculation of a certain tumor and resist the inoculation of the same tumor into the testicle. Undoubtedly this method of inoculation will reveal the existence of a number of other phenomena. The discovery of specific therapeutic measures is certainly the greatest problem in cancer research. A great deal of work has been done already on the subject, and the latest investigations of Wassermann on the chemotherapy of experimental tumors seem to be of great promise. But here also the therapeutic methods must be tried on animals in which the inoculations of tumor cells have been made into parenchymatous organs before the growths thus treated will have any analogy to human cancer. In this connection one must bear in mind the fact that all the empirical so-called specific cancer remedies, which are continually being devised, are usually successful in treating localized skin cancers and fail utterly in the malignant growths of the internal organs. It is comparatively easy to produce a localized necrosis and softening in a circumscribed growth of the skin and subcutaneous tissue, but whether the same result will be produced on a diffuse and better nourished tumor growing inside of a parenchymatous organ cannot be decided a priori. To determine this it is necessary to have experimental proof on animals in which the tumor was inoculated into organs.