When the growth takes place from the skin or mucous membranes, the surface frequently presents numerous and usually arborescent papillæ or villi. The papillary cancers of the skin and the villous cancers of mucous membranes are thus distinguished.
Cancerous growths of the skin and transitional membranes, often called epithelioma or cancroid, usually contain epithelioid cells resembling epidermis, and are therefore designated as epidermoid or pavement-celled cancer. The alveolar contents of certain cutaneous cancers are cells resembling those of the deeper layers of the rete mucosum, while those of other cancers of the skin resemble rather the epithelium of sweat-glands. Growths of the former character extend laterally, ulcerate early, and are known as superficial cutaneous cancer. They form one of the varieties of the so-called rodent ulcer. Cutaneous cancers, simulating in their structure a reproduction of the epithelium of sweat-glands, represent a variety of glandular cancer. The latter term is applied to cancerous growths which arise in glandular organs, with suggested resemblances of their cells to the gland-cells of the respective organ. Cylindrical-celled cancer is frequently met with in those parts of which a cylindrical epithelium is a normal constituent.
The degenerations of the epithelioid cells and stroma suggest qualifying terms. The mucous and colloid cancers are those whose alveolar contents or stroma have undergone a mucous or colloid degeneration. The keratoid cancer is one which presents the horn-like transformation of its epidermoid cells. The melanotic cancer contains abundant pigment, melanin, within its cells.
These differences in the structure and appearance of the tumor are frequently associated with certain modifications of growth and clinical properties. The epidermoid cancers are less likely to recur after early removal; the medullary cancers are of rapid growth and prone to ulceration; while the fibrous or scirrhous forms are of extreme slowness of growth. In general, however, the pathological importance of cancerous tumors is essentially the same wherever the seat and whatever the peculiarities of structure.
TERATOID GROUP.
Includes those tumors, usually of congenital origin and apparent at birth, composed of connective tissue, epithelium, nerves, muscle, and vessels. These tissues are often so grouped together as to suggest systems of the body and parts of an individual. Cysts are often present which simulate cavities found in the body, whether of normal or pathological origin.
In this group are the dermoid cysts with their various contents, epidermis, sebum, hair, teeth, and bone. The solid teratomata, with all varieties of connective tissue, as fibrous tissue, fat tissue, cartilage, bone, neuroglia, in addition to nerves, muscle, and vessels. Squamous, cylindrical, and ciliated epithelium may be present and line cavities, at times tubular, whose walls are formed of skin or mucous membrane. Other tumors of this group are commonly included under monstrosities, and comprise the varieties of duplication of parts of the body, of which the extreme instances are such double monstrosities as the Siamese Twins, Ritta and Christina, the Spanish Cavalier, and the like.
INFECTIVE GROUP.
The chief characteristic is the cause, micro-organisms, which, introduced into the body, produce, through their dissemination and development, multiple growths of tissue like those resulting from persistent inflammation. As their structure corresponds with the productive results of inflammation, and their cause is analogous to the infective causes of inflammation, these morbid growths are closely allied to inflammatory disturbances. Their classification among tumors is desirable, as they represent circumscribed growths whose appearance, persistence, and effects closely resemble those characteristics of the morbid growths, in the limited sense, in which the new formation of tissue occupies a wider range:
Granuloma of tuberculosis, scrofula, leprosy, glanders, actinomycosis, syphilis, lupus.
Lymphoma of diphtheria, scarlet fever, typhoid fever.