Age.—The liability to different sorts of tu mors varies very considerably with different periods of life. In childhood and in early adult life carcinomata are rarely seen and of the malignant tumors sarcoma predominates, while the reverse is the case after the age of 30. To this rule there are many exceptions, however. When young people do acquire carcinoma the disease is always of extremely virulent type, whereas in the very aged its development is slower and in particular the formation of me tasases is much less extensive.
Sex.— Carcinoma ismuch more frequent in women than in men and the organs of predilec tion also differ in the sexes. In men the tongue, lips and stomach are oftenest attacked, while in women the disease is most commonly seen in the breast or uterus.
Heredity.— The tendency of modern pathol ogists is to ascribe less and less importance to heredity as a cause of tumor formation. Statistics are particularly misleading in this re gard and while it is undoubtedly true that in a considerable proportion of cancer cases more or less remote members of the same family have been similarly affected, a like inquiry into the antecedents of healthy persons would show ap proximately similar results. A celebrated case is that of Napoleon I — who, as well as his father and two sisters, died of carcinoma of the stomach. Carcinoma is a common disease and, therefore, appears frequently in the same fam ily; sarcoma is rare and so has less appearance of hereditary transmission.
Increase of Malignant sta tistics of recent years show that throughout the world, but particularly in England, there seems to be a marked increase in the occurrence of carcinoma. Roswell Park says that if the ratio of increase in the number of cancer deaths in New York State continues unchanged for the next 10 years the mortality from this cause will be greater than that ofpulmonary tuberculosis, smallpox and typhoid fever combined. These figures cannot be accepted without some reser vation, however, for undoubtedly the diagnosis is now made incases that were formerly un classified, autopsies are more frequent and the causes of death are more definitely indicated in death certificates. Also through municipal sanitation, improved methods of medical treat ment, more widespread dissemination of the laws of hygiene, etc., a greater number of peo ple now live to reach the age when carcinoma is frequent. The increase seems to affect prin cipally those of the upper ranks, in contradis tinction to tuberculosis which spreads most ac tively among the proletariat.
In conclusion, it may be said that probably no one cause underlies the formation of all types of tumors, but that possibly widely differ ing factors may be concerned in the production of the different varieties.
Classification of our knowl edge of the causes of tumors becomes more exact, a satisfactory classification is impossible. The so-called histogenetic classification based on embryological data is open to many tions, as well as various other systems pro posed. The following table is taken from Delafield and Prudden's 'Handbook of Patho logical Anatomy and Histology.' Teratomata and Cystomata.
It will be observed that the designation for each form is derived by adding the suffix to the technical name of the corresponding tis sue type, and for mixed tumors compound names are formed, as adeno-carcinoma, myxo sarcoma, etc.
Different Varieties of Tumors.— Malignant Tumors — Sarcoma.— Sarcomata are tumors of the connective tissue group, composed of cells, embryonal in type, which are disproportionally i numerous in comparison to the basement sub stance, so that the tumor as a whole is usually soft and pulpy in contradistinction to the stony hardness of carcinomata. They are character ized by extreme vascularity, the new formed vessels often being mere channels between the tumor cells, and the tendency to form metas tases by means of the blood current rather than the lymphatics. Their cells may be of many varieties and the following chief types are recognized: (1) Large and small spindle celled; (2) large and small round celled; (3) giant celled; (4) milano sarcomata, which con tain pigment, frequently arise from pigmented moles and are extremely malignant. Mixed tumors, such as osteo-sarcomata, angio-sarco mata, etc., frequently occur. Sarcomata may arise from bone, the brain and spinal cord, the breast, the kidney, uterus and lymph glands. They grow rapidly, owing to their vascular structure, are prone to necrotic changes and if situated on the surface of the body break down and ulcerate. Sarcoma is not common, is a disease of early life, rarely appearing after the age of 40, and frequently is a sequel of injury or inflammation. In many respects sarcoma behaves like a growth due to some parasitic infection.