In English works the term Epithelioma is chiefly used to designate cancers of the cutaneous surface, tongue, and oesophagus, places where the surface is covered with flat epithelium. Similar tumours occur in the larynx, uterus, and vagina, and urinary bladder. It is possible to distinguish a penetrating or infiltrating form, and a more superficial form. This latter form is almost equivalent to Rodent ulcer of English authors, and Flacker Krebs of Thiersch and the German authors.

Fig. 110. - Ulcerated cancer of stomach. The central depression of the ulcer and the prominent infiltrated border are shown.

The common epithelioma of the lip is the most familiar example of the infiltrating form. In this form cylindrical processes of epidermis, taking origin in the surface epithelium (see Fig. 105, p. 253), grow downwards into the true skin, infiltrating it and destroying its connective tissue. These processes, as they grow, exercise a concentric pressure on their own cells, and so produce closely-packed globular bodies, composed of epidermic cells, wrapped round each other. These bodies, variously called Epidermic globes, Laminated capsules, etc., are very characteristic of this form of epithelioma. The cells in the globes are usually horny, and the consequent bright translucent appearance, as well as the bright yellow colour in sections treated with picric acid, attract the eye in microscopic sections. In some parts there is, along with the production of these penetrating processes, a formation of papillae on the surface. This is often manifest in the epitheliomas of the scrotum and certain other parts of the skin. It is also very pronounced in some of the vagino-uterine cancers, forming the so-called Cauliflower cancers. In the urinary bladder there is frequently such a marked production of elongated papillae that the surface is quite shaggy, while the mucous membrane beneath is infiltrated. To this form the name Villous cancer is often given. The papillae, like those of the simple papilloma of the bladder, are liable to haemorrhage.

All these epitheliomas are prone to ulceration, and frequently present themselves as ulcers with infiltrated walls.

Rodent ulcer is a special form of epithelioma which occurs in the upper part of the face, and more rarely in other parts of the body. It presents itself as an ulcer with overhanging edges, so much overhanging as to appear "rolled over." The edge shows the epithelial structures in the form of peculiar small epithelial cells arranged in well-defined groups (see Fig. Ill), the peripheral cells of which are sometimes columnar. These groups of cells are beneath the epidermis, and seem in many cases to have no connection Mith the Malpighian layer. The tumour is a superficial one, there are no penetrating cylinders, no laminated capsules, and there is no tendency to invade the lymphatic glands.

The name Cholesteatoma or Pearl tumour has been given to a form which is variously regarded as an epithelioma or a cystic tumour. It contains bright, glancing, pearl-like structures, consisting mainly of cholestearine and fat. Besides these, there are flat cells, epithelial in character, which are arranged into rounded bodies, inside which the cholestearine is contained. These tumours are sometimes surrounded by a capsule so as to resemble atheromatous cysts-They are most typically seen in the soft membranes and substance of the brain, but also occur in the subcutaneous tissue, testicle, ovary, parotid, and ear. (See Virchow, in Virch. Arch., viii.; Eberth, do., xlix.; Eppinger, Prag. Vierteljahrschr., 1875; Chiari, Cholesteatom des Ruckenmarks, Prag. rned. Wochenschr., 1883; Bristowe, Path, trans., v., 24, 1854; Price, do., xxxviii., 24, 1887).