Major Orifice Research Articles

Ectodermal Tumors of the Skin

Introduction The epidermis contains a basal-cell layer overlaid by squamous cells, and this in turn is covered with varying amounts of keratin. Beneath is the corium composed of connective tissue in which are embedded the skin appendages including the sebaceous glands, sweat glands and hair follicles. Neoplasms of the epidermis tend to form squamous cells and keratin and therefore are referred to as squamous-cell tumors or as keratoses. They are usually found upon the surface of the skin. Tumors of the skin appendages, derived from the basal cells of the epidermis destined to form appendages often retain their basal-cell characteristics and are referred to as basal-cell tumors. They may be found on the surface or beneath the epidermis. Since the structures of both the epidermis (squamous cells and keratin) and the appendages within the corium are derived from the same basal-cell layers of the skin, it is convenient to divide neoplasms of the skin into epidermal tumors (squamous-cell lesions) and appendage tumors (basal-cell lesions). The term acanthoma is sometimes used for epidermal cancer and corium carcinoma or rodent ulcer for appendage cancer. At the major orifices of the body (such as the mouth and anus) epidermal covering is modified to form the mucous membranes which are continuous with the modified entodermal coverings of similar structure. Epidermal and appendage tumors, therefore, may also occur in the mucosa of the eye, lips, oral and nasal cavities, pharynx, larynx, trachea, bronchi and esophagus, and on the mucous surfaces of the anus, vagina, penis, urethra, etc., although some of these structures are derived from the entoderm. Similar tumors may also occur on the mucous linings of the bladder, uterine cervix, ureter, and renal pelvis, although some of these mucous membranes are of mesodermal origin. Inclusions of epidermal tissue below the surface (both epidermoid cysts and remnants of the branchial clefts) may also provide a nidus for such growths. The basic histologic varieties of epidermal and appendage-cell tumors have, therefore, an exceedingly wide distribution in the human body. Malignant lesions of this type taken as a group constitute one of the most frequent forms of cancer in man. Subvarieties of epidermal carcinoma in which keratin formation is absent are sometimes referred to as transitional, cuboidal, or mixed-cell cancer. While most common on the mucous surfaces, such structures also occur in rapidly growing and undifferentiated carcinomas of the epidermis (so-called Grades III and IV). Non-keratinizing epidermal cancer overlying lymphoid tissue, as in the tonsil, was named by Regaud of France, in 1921, lympho-epithelioma. In more slowly developing cancer the malignant squamous cells may be found entirely within the epidermis, a form of cancer described in the nipple by Paget (1876) in England, and in the skin by Bowen (1912), in America.