XII. CLASSIFICATION OF TUMORS. A RATIONAL, Systematic classification of tumors is to the surgeon what the analytical key is to the botanist. A uniform system of classification of tumors is one of the great wants of modern pathology, and all attempts in this direction have proved failures. New classifications are being introduced from time to time, but each of them invariably represents the individual author's own views regarding the origin and nature of tumors. A classification which will be intelligible to the student and of practical utility to the surgeon must be based on the histogenesis and the clinical aspects of tumors. As the histologist traces the normal tissue to its embryonic origin, so the pathologist must follow the tumor-cells to the embryonic matrix which produced them, in order to trace tumors to their primary histogenetic origin and to classify them upon a histological basis. The botanist includes in the same class wholesome and poisonous plants from their morphological resemblance, and the pathologist groups together tumors which have a common embryonic origin; but in making a classification he must make a subdivision according to their clinical aspects, which means their relation to the surrounding tissues and the organism. To Virchow belongs the honor of having attempted the first systematic classification of tumors on a histological basis. VIRCHOW'S CLASSIFICATION. I. Histioid; 2. Organoid; 3. Granulomata; 4. Teratoid; 5. Combination tumors; 6. Extravasation- and exudation-tumors; 7. Retention-cysts. Among the histioid tumors he included all tumors composed of one kind of cells. The class of organoid tumors he made to include all tumors composed of several kinds of tissue-elements with a definite typical arrangement of the component parts. Among the infective swellings he included carcinoma and sarcoma, calling this group "granulomata." "Teratoma" was the term applied to tumors composed of a system of organs arranged in an imperfect manner, of course, and representing different parts of the body, and sometimes a perfect body, such as dermoid cysts and fœtus in fœtu. "Combination tumors," as the term implies, are tumors composed of different kinds of tumor-tissue representing two or more histioid tumors, such as adeno-chondroma, myofibroma, etc. The extravasation- and exudation-tumors include swellings containing blood, serum, or inflammatory products. A pure histioid tumor, according to Klebs, could be found only in a very small epithelioma and a small sarcoma. In large tumors it is represented by angioma. The term "organoid" as applied to tumors is incorrect and misleading, because even the most perfectly-developed adenoma, as well as all the rest of the tumors, lacks physiological function. Compound tumors occur in consequence of degenerative changes or of change in the type of tissue-growth in a primary simple tumor. The granulomata and the extravasation- and exudation-swellings, which should no longer be classified with tumors, will be eliminated from our classification. Retention-cysts are not tumors, but have so much in common with tumors, and occupy such a conspicuous place in the differential diagnosis, and require so frequently the same treatment as tumors, that they will be treated under a separate head in this book. The classification of tumors as prepared by a committee of the College of Physicians and Surgeons of London is very defective, as among tumors it includes swellings the product of other pathological conditions. Williams and Klebs classify tumors into archiblastic and parablastic, in accordance with the division by His of tissue in the embryo. For the sake of simplifying the location of tumors anatomically in the diagnosis, as well as in pointing out the differences of structure and function of the cells of the epiblast and hypoblast, we shall retain the distinction between epiblastic and hypoblastic tumors. Virchow from a practical standpoint divided all tumors again into1. Homologous; 2. Heterologous-terms which have been used wrongly as synonymous with the designation "benign" and "malignant." All malignant tumors are heterologous, but not all heterologous tumors are malignant. According to Virchow, a heterologous growth is a tumor which in its histological structure deviates from the type of tissue from which it grows, while a homologous tumor is one which reproduces the type of tissue of the part or organ in which the tumor is located. The innocent tumors histologically very closely resemble normal tissue; no such resemblance can be seen in the malignant tumors. The former are homologous, the latter heterologous; but there are instances where an innocent tumor is heterologous (chondroma), and malignant tumors present a homologous appearance during the earliest stages of their development. A familiar illustration of what is meant by the term "homologous" is furnished by a myofibroma of the uterus, because it contains all the tissue-elements of that part of the uterine wall with which it is in contact. A chondroma in any of the glands-as the parotid, mammary, and testicle-represents a benign heterologous tumor, because cartilage is not a normal histological constituent of these glands. According to Cohnheim, all chondromata are heterologous tumors, as they never spring from cartilage where it normally exists, but occur in bone and soft tissues where cartilage has no legitimate physiological existence. Using the term "heterologous" in a strictly practical sense, the only tumors that are destructive are those which are heterologous in their origin and location. The homologous tumors. may become destructive only by accident. Heterotopic tumors are heterologous tumors. "Heteroplasty" is another term introduced by Virchow, and in its strictest sense it takes in the malignant tumors. According to the views of this author as to the origin of malignant tumors, in cases of sarcoma and carcinoma during the earliest stages we meet with indifferent cells which, according to the nature of the initiative, assume an epithelial or connective-tissue type. It must be remembered that Virchow entertained the belief that carcinoma and sarcoma have a common origin in connective tissue, and that during a later stage the new products differ as their cellular elements reach various degrees of development. Robin and Waldeyer showed conclusively that epithelial tumors are never developed from a connective-tissue matrix. Lancereaux, Klebs, and others have excluded from the mesoblastic tumors endothelioma, as being a separate type closely resembling epiblastic and hypoblastic Lancereaux described endothelial tumors of the lymphatics of the peritoneum; Robin, of the arachnoid and peritoneum; Gaucher, of the spleen from the endothelia of blood-vessels and lymphatic glands; Monod and Arthraud, of the retina from the vascular endothelia. tumors. Sutton claims that the same relation exists between sarcoma and endothelioma as between carcinoma and epithelioma. We shall include endothelioma among the malignant mesoblastic tumors, and thus adhere strictly to the classification made in accordance with the division of embryonic tissue into the three germinal layers. We shall also endeavor to show that the endothelial cells are capable of being trans formed into ordinary connective tissue, and vice versâ, and that their close histological and pathological relationship to the connective-tissue tumors would, a priori, tend to prove that they are subject to tumorformation of the same type as the common connective tissue of similar histogenetic origin. From a practical standpoint, the division of tumors according to their clinical aspects manifested by their relations to the adjacent tissues and to the organism has always been, and always will be, of the greatest importance to the surgeon. Clinically, tumors have been divided into-1. Benign; 2. Malignant; 3. Suspicious. We have explained elsewhere why the third class should be abolished. A tumor is either benign or malignant. The tumors classified heretofore as suspicious are tumors which from their structure or location present conditions not favorable for thorough removal by the usual operations made for the removal of benign tumors. Such tumors as chondroma and myxoma, about which there has always lingered a suspicion as to their benign nature, from a practical standpoint have been regarded as innocent growths, and incomplete removal is responsible for many relapses after operation. The sudden change in the clinical behavior of tumors which have been pursuing a benign course for perhaps a long time is no evidence of a semi-malignant nature of the tumor, but is an evidence that a benign tumor has undergone transition into a malignant stage, or that the tumor was malignant from its incipiency, and has passed from a latent into an active condition. All the embryonic germinal layers furnish matrices for benign and fór malignant tumors. The clinical type of the tumor depends upon the stage of arrest of development of the cells composing the matrix derived from the embryo or from embryonic cells of post-natal origin. The cells composing the tumor-matrix produce a tumor that is either benign or malignant. We shall speak of benign and malignant tumors of the epiblast and hypoblast and the mesoblast. A benign tumor is one which never extends beyond the germinal layer in which it had its origin, while a malignant tumor extends to and involves tissues derived from germinal layers other than the one from which it had its origin. The extension of a tumor to adjacent tissues irrespective of their structure or their embryonic origin has been regarded for a long time as the most reliable clinical proof of the malignant nature of the tumor. We shall classify tumors with special reference to their origin from the different germinal layers-the epiblast, the hypoblast, and the mesoblast-and to the stage of arrest of development of the cells composing the tumor-matrix. The lowly-organized tumor-tissue will represent the malignant tumors, and tumors composed of highly-organized cells will include all benign growths. In the description of the different varieties |