The term cancer is a clinical one, expressing the malignant characters of the tumour. Like sarcoma it was formerly applied in a general way, and included most sarcomas. The delimitation of the sarcomas by Virchow has led to a stricter definition of the cancers.
The carcinoma is a tumour taking origin in epithelium and having an epithelial structure, but in the arrangement of the structure and in its mode of growth presenting atypical characters.
The Cells of cancers are epithelial in origin and structure, but differ according to the form of epithelium from which they are derived. Thus we have flat or pavement cells, cylindrical cells, and glandular epithelial cells. Again, the cells do not always correspond strictly with the typical cells of the same kind, but as they are produced in great numbers, and as, correspondingly to the general type of epithelium, they lie close against each other, they often present great varieties in shape and size. This applies especially to the glandular forms. The various forms of cells will be again referred to in describing the varieties of cancers. The cells always grow in larger or smaller masses, lying close together without intercellular substance, so as to form the so-called "cell-nests," which are characteristic of cancers (Fig. 103). The cut surface of cancers when scraped by the knife often yields a fluid, the so-called Cancer-juice, in which are present groups of cells as they have been removed from the spaces in which they lie.
Fig. 103. - Section of cancer of mamma from a recent nodule. Epithelial cells in spaces formed by connective tissue; these are sometimes in single rows, and by multiplication form larger masses, x 200 (Cornil and Ranvier).
The Stroma encloses the cell masses, and supports the bloodvessels necessary to the nourishment of the tissue. The cell masses are epithelial, and they may be derived from epithelial cells which have been transported from a distance, as is the case in secondary cancers, but the stroma is always derived from the local connective tissue and local blood-vessels. The stroma may be nothing more than the pre-existing connective tissue of the part, perhaps with some inflammatory increase, as indicated by the presence of round cells, but in other cases, and especially in secondary tumours, it forms a well-defined meshwork of characteristic appearance, as shown in Fig. 104. The stroma may be formed, not of ordinary connective tissue, but of bone and cartilage, this fact showing that the stroma is of purely local growth, and also that bone and cartilage have close relations to ordinary connective tissue.
Fig. 104. - Stroma of a soft cancer of the mamma after the cells had been washed out. x S2.
In a case observed by the author of cancer of the stomach with secondary tumours in the ribs, the secondary tumours formed enlargements of a firm character. Microscopic examination showed trabecules, formed partly of bone and partly of cartilage, which radiated from the surface of the rib. Between these trabeculae were the characteristic epithelial structures of the cancer.
Where a cancer produces a well-formed stroma along with the epithelial masses, it will probably grow more readily into a distinct tumour than where the epithelial masses depend for their nourishment on the existing blood-vessels. In this latter case the cancer will commonly present more the characters of an infiltration of the tissues with epithelial structures, and this infiltration may be associated with such irritation as to lead to considerable new-formation of hard connective tissue, giving sometimes a markedly fibrous character to the structure, as in scirrhous cancer.
The Blood-vessels in cancers run, as has been indicated, in the connective tissue stroma. They consist of wide capillaries with the usual arterial and venous connections. The great tendency which cancers present to extend by the lymphatic system suggests some special structural connection with the Lymphatic vessels. According to Cornil and Ranvier such a connection can be demonstrated by injection. If a cancerous tumour, before being laid open, be punctured with the needle of a hypodermic syringe and a watery solution of Prussian blue be injected, the material first runs into the alveoli around the puncture, mapping out, as it were, a series of cavities, and then passes on into the lymphatic vessels, issuing by their extremities -divided in removing the tumour.