The varieties of cancer are distinguished according to the character and arrangement of the epithelial cells.
The squamous epithelial cancer or epithelioma originates from a surface covered by squamous epithelium, such as the skin, or the mucous membrane of the mouth, gullet, or larynx. The cancer cells retain the characters of squamous epithelium, and, being confined within the lymph spaces of the sub-epithelial connective tissue, become compressed and undergo a horny change. This results in the formation of concentrically laminated masses known as cell nests.
The clinical features are those of a slowly growing indurated tumour, which nearly always ulcerates; there is a characteristic induration of the edges and floor of the ulcer, and its surface is often covered with warty or cauliflower-like outgrowths (Fig. 58). The infection of the lymph glands is early and constant, and constitutes the most dangerous feature of the disease; the secondary growths in the glands exhibit the characteristic induration, and may themselves break down and lead to the formation of ulcers.
Epithelioma frequently originates in long-standing ulcers or sinuses, and in scars, and probably results from the displacement and sequestration of epithelial cells during the process of cicatrisation.
The columnar epithelial cancer or columnar epithelioma originates in mucous membranes covered with columnar epithelium, and is chiefly met with in the stomach and intestine. As it resembles an adenoma in structure it is sometimes described as a malignant adenoma. Its malignancy is shown by the proliferating epithelium invading the other coats of the stomach or intestine, and by the development of secondary growths.
Glandular carcinoma originates in organs such as the breast, and in the glands of mucous membranes and skin. The epithelial cells are not arranged on any definite plan, but are closely packed in irregularly shaped alveoli. If the alveoli are large and the intervening stroma is scanty and delicate, the tumour is soft and brain-like, and is described as a medullary or encephaloid cancer. If the alveoli are small and the intervening stroma is abundant and composed of dense fibrous tissue, the tumour is hard, and is known as a scirrhous cancer—a form which is most frequently met with in the breast. If the cells undergo degeneration and absorption and the stroma contracts, the tumour becomes still harder, and tends to shrink and to draw in the surrounding parts, leading, in the breast, to retraction of the nipple and overlying skin, and in the stomach and colon to narrowing of the lumen. When the cells of the tumour undergo colloid degeneration, a colloid cancer results; if the degeneration is complete, as may occur in the breast, the malignancy is thereby greatly diminished; if only partial, as is more common in rectal cancer, the malignancy is not appreciably affected. Melanin pigment is formed in relation to the cells and stroma of certain epithelial tumours, giving rise to melanotic cancer, one of the most malignant of all new growths. Cyst-like spaces may form in the tumour by the accumulation of the secretion of the epithelial cells, or as a result of their degeneration—cystic carcinoma. This is met with chiefly in the breast and ovary, and the tumour resembles the cystic adenoma, but it tends to infect its surroundings and gives rise to secondary growths.
Rodent cancer originates in the glands of the skin, and presents a special tendency to break down and ulcerate on the surface (Figs. 102 and 103). It almost never infects the lymph glands.