OF; BONES, DISEASES OF). It is only found in the interior of bones, chiefly in those of the arm and leg. The degree of malignancy is low, dissemination possibly never occurs, and re currence after operation is rare.
II. Epithelial Tumours.— Papilloma.—The familiar exam ple of a papilloma is the wart, which is formed by a prolifera tion of a few papillae of the skin together with the overlying squamous epithelial layers (fig.
3). It seems probable that some warts are of an infective nature, for instances of direct con tagion are not uncommon and in special regions they occur in the definitely infective diseases gonorrhoea and syphilis. Occasionally warts are pigmented, and as noted above the melanoma is apt to start in such a wart.
Papillomata are also found in the bladder (fig. 14), as long deli cate filaments growing from the bladder wall. These consist of a connective-tissue core covered by a thin layer of epithelium.
Adenoma.—(Figs. Ia and 'b.) The glandular tumours are com mon in the breast, the ovary and the intestinal canal. The struc ture of an adenoma of the breast has already been described (vide supra), and the structure of other adenomata is on the same general plan, subject to the difference imposed by the tubular or acinous character of the gland con cerned (see GLAND). The main features of an innocent glandular tumour are : (a) the presence of a rounded, painless swelling with a well-defined margin; (b) the swelling is freely movable in the surrounding tissues, not attached to skin; (c) neighbouring lym phatic glands are not enlarged.
Carcinoma.—The following va rieties of carcinoma are de scribed :— i. Squamous-cell carcinoma (fig. 4), arising from those parts of the body covered by squamous epithelium, namely the skin, lips, tongue, mouth, pharynx, oesophagus, vagina, anus and bladder.
ii. Spheroidal-cell carcinoma (figs. 2a and 2b), arising from spheroidal epithelium, as in the breast, pylorus, pancreas, liver and prostate.
iii. Columnar-cell carcinoma (figs. 15 and 16), arising from columnar epithelium, as in the intestine, stomach and ducts of the breast.
The general histology of these tumours corresponds to that of a spheroidal-cell carcinoma already described (vide supra), variation between the three groups being dependent on the character of the cells. Thus Keratinization is a common feature of squamous cell carcinoma and when colloid degeneration of a carcinoma oc curs it is always either a sphe roidal or a columnar cell growth.
Amongst spheroidal cell carcino mata great variation occurs in the amount of fibrous tissue present ; when fibrosis is very great the growth is often termed a "scirrhus." The clinical charac teristics of a carcinoma, whatever its situation, are : (a) the pres ence of a swelling which has no well defined margin, but fades away into the surrounding tissues to which it is fixed; (b) when the tumour lies in or near the skin it becomes fixed to this and ulcerates at an early date; (c) the tumour is painful and tender though the degree of pain varies widely, and in the early stages there may be none; (d) the neighbouring lymphatic glands soon become enlarged and tender, showing that they are the seat of metastatic de posits.
iv. Rodent cancer or rodent ulcer, often called basal cell carcinoma, is a special variety of squamous cell carcinoma arising from the germinal layer of the skin prob ably in the close relation to the sebaceous glands. It shows itself as a slowly pro gressing ulceration of the skin, and is especially common on the face near the eye or ear. The condition is one of purely local malignancy, and dissemination does not occur.
Since endothelial cells lie next one another without intervening substance they resemble in this respect epithelial cells but em bryologically they are mesodermal and therefore allied to the con nective tissue group. The features of en dothelial tumours therefore might be ex pected to resemble now the one, now the other group and, indeed, there is some tendency to refer to the endotheliomata unusual varieties of growth which cannot well be placed in recognized groups. Nev ertheless a primary subdural growth or one of the pleural cavity cannot be glan dular however much it may resemble a car cinoma microscopically. Growths involv ing proliferation of the endothelium lining blood and lymphatic channels (perithelio ntata) are perhaps the most convincing examples of endothelioma.
See also CANCER; CANCER RESEARCH.